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AVAILABILITY, EFFICIENCY, AND FATE OF ALTERNATIVE NITROGEN SOURCES IN SEEPAGE IRRIGATED POTATO PRODUCTION
By
ZHIWEI CHEN
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2010
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© 2010 Zhiwei Chen
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To my family, for the support whenever I need
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ACKNOWLEDGMENTS
I thank my advisor, Dr. Daniel J. Cantliffe, for his great support in my research and
study. His insight and good advice helped me successfully analyze my experimental
results and move into the next stage of my career. I also thank Dr. Chad Hutchinson for
introducing me into the potato study in Florida and guiding me in my research work. He
allowed me the way to think freedom on research and supported my ideas to broaden
my research experience. I thank other committee members and professors Dr. Ying
Ouyang, Dr. Bielinski Santos, Dr. Peter Stoffella and Dr. Rao Mylavarapu for their
support of this work.
Meanwhile, I want to thank for the staff in Hastings research farm Douglas
Gergela, Alison Beyer, Jill Lewis and Bart Herrington for their hard work and great
support for my research. I also want to thank Katie Dawson and Dana Fourman for their
nice help in my extensive sampling and testing work. Special thanks also go to my
friends, Kesi Liu, Min liu and Li Ma for their great friendship during my life in Gainesville.
Finally, I would like to thank Li Li, for her trust and love. She gave me so many
things that I can have my confidence, support to finish my study. Those also made my
study in UF the happiest times of my life. My deep love for her is beyond any words in
the world. I will forever cherish our memories and I know there are many more to come.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS.................................................................................................. 4
LIST OF TABLES............................................................................................................ 8
LIST OF FIGURES........................................................................................................ 11
ABSTRACT ................................................................................................................... 12
CHAPTER
1 INTRODUCTION .................................................................................................... 15
2 LITERATURE REVIEW .......................................................................................... 19
Potato Nitrogen Management ................................................................................. 19 Monitor Potato N Status.......................................................................................... 22 The TCAA Production Area .................................................................................... 24 Florida Best Management Practices ....................................................................... 25 Controlled-release Fertilizer.................................................................................... 28
Urea-Formaldehyde Reaction Nitrogen Products (UFs)................................... 29 Sulfur-Coated Nitrogen Products (SCU)........................................................... 30 Polymer-Coated Nitrogen Products (PCUs) ..................................................... 31 Polymer/sulfur-Coated Nitrogen Products (PSCU)........................................... 33 Urea-Other Aldehyde Reaction Products ......................................................... 34
Nutrient Release Formula of CRF........................................................................... 35 Nitrogen Use Efficiency........................................................................................... 37 Nutrient Loss under the Leaching Events ............................................................... 38 Research Objectives............................................................................................... 39
3 SIMULATION OF NITROGEN RELEASE FROM POLYMER-COATED FERTILIZERS IN A CONTROLLED SYSTEM........................................................ 41
Introduction ............................................................................................................. 41 Materials and Methods............................................................................................ 43
Experimental Procedure................................................................................... 43 Statistical Design and Analysis......................................................................... 44 Development of Linear Formula for Release Rate (K)...................................... 45
Results and Discussion........................................................................................... 46 CNR91.............................................................................................................. 46 Asymptote (a) from Gompertz Model ............................................................... 48 Growth Rate Parameter(c) from Gompertz Model............................................ 49 Days to Reach 25% TAN and 50% TAN .......................................................... 49 Evaluation of Fertilizer Candidates................................................................... 50 Q10 Value.......................................................................................................... 53
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Linear Formula for Release Rate ..................................................................... 54 Mathematical Model under Variable Temperature............................................ 56 Model Verification............................................................................................. 58
4 APPLICATION OF CONTROLLED-RELEASE FERTILIZER FOR NORTHEAST FLORIDA CHIP POTATO PRODUCTION.............................................................. 67
Introduction ............................................................................................................. 67 Materials and Methods............................................................................................ 69
Site Description ................................................................................................ 69 Experimental Design and Layout...................................................................... 69 Crop Seasonal Management............................................................................ 70 Tissue and Water Sampling ............................................................................. 70 Tuber Yield and Quality Analysis...................................................................... 71 Statistical Analysis............................................................................................ 72
Results and Discussion........................................................................................... 72 Tuber Production.............................................................................................. 73 Tuber Specific Gravity (SG).............................................................................. 74 External and Internal Tuber Quality.................................................................. 76 Leaf Tissue N Analysis ..................................................................................... 77 Plant Tissue N Removal (TNR) and Nitrogen Recovery Efficiency (NRE)........ 79 Water Quality Analysis ..................................................................................... 80 Soil N Analysis ................................................................................................. 81
5 EVALUATION OF ALTERNATIVE FERTILIZER PROGRAMS FOR NORTHEAST FLORIDA POTATO PRODUCTION ................................................ 94
Introduction ............................................................................................................. 94 Materials and Methods............................................................................................ 97
Production Management .................................................................................. 98 Measurement during the Growing Season ....................................................... 98 Statistical Analysis.......................................................................................... 101
Results and Discussion......................................................................................... 101 ‘Atlantic’ .......................................................................................................... 101
Tuber production and quality.................................................................... 101 Tissue nutrient analysis ........................................................................... 104 Soil nutrient analysis ................................................................................ 108
‘Harley Blackwell’ ........................................................................................... 110 Tuber production and quality.................................................................... 110 Tissue nutrient analysis ........................................................................... 112 Soil nutrient analysis ................................................................................ 114
‘FL2053’.......................................................................................................... 115 Tuber yields and quality ........................................................................... 115 Tissue nutrient analysis ........................................................................... 117 Soil nutrient analysis ................................................................................ 118
Perched Water Table Quality ......................................................................... 118
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6 CHARACTERIZATION OF IN-ROW MOVEMENT OF NITROGEN DURING A RAIN EVENT AND ITS IMPACT ON NORTHEAST FLORIDA SEEPAGE IRRIGATED POTATO PRODUCTION.................................................................. 137
Introduction ........................................................................................................... 137 Materials and Methods.......................................................................................... 139
Site Description .............................................................................................. 139 Experimental Design ...................................................................................... 140 Drainage Lysimeter Installation and Water Sampling..................................... 141 Soil Sampling ................................................................................................. 142 Tuber Yield and Quality .................................................................................. 142 Statistical Analysis.......................................................................................... 143
Results and Discussion......................................................................................... 143 Tuber Production and Quality......................................................................... 143 Nutrient Concentration and Leaching ............................................................. 145 Soil Nutrient Analysis ..................................................................................... 147
Conclusions .......................................................................................................... 148
7 SUMMARY AND CONCLUSIONS........................................................................ 154
LIST OF REFERENCES ............................................................................................. 163
BIOGRAPHICAL SKETCH.......................................................................................... 170
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LIST OF TABLES
Table page 3-1 Fertilizer treatments, manufactures, and rates in the fertilizer program
evaluation in Hastings, FL, in 2006..................................................................... 60
3-2 Q10 values for various PCUs at 7 days sampling time. ....................................... 63
3-3 Nitrogen release rate K associated with constant temperature for different PCU productsz. ................................................................................................... 65
3-4 Nitrogen release rate K associated with variable temperature for different PCU productsz. ................................................................................................... 65
4-1 Fertilizer treatments, manufacturers, and rates evaluated in Hastings, FL, in 2006z. ................................................................................................................. 85
4-2 The influence of fertilizer source and fertilizer rate on ‘Atlantic’ tuber yield, size distribution, and tuber specific gravity (SG), in Hastings, FL in 2006. ......... 86
4-3 The influence of fertilizer source and rate on ‘Atlantic’ potato tuber percent external and internal tuber defect (%) of total yield, in Hastings, in FL 2006. ..... 87
4-4 The effects of fertilizer source and fertilizer rate on ‘Atlantic’ potato leaf N concentration (% of tissue dry weight), in Hastings, FL, in 2006. ....................... 88
4-5 The plant tissue N removal (TNR) and N recovery efficiency (NRE) of ‘Atlantic’ potato on a per-hectare basis when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006. .......................................... 89
4-6 The water sample NH4-N and NO3-N concentrations (mg L-1) at perched water table for ‘Atlantic’ potato grown under fertilizer source and fertilizer rate treatments in Hastings, FL, in 2006. ................................................................... 90
4-7 The soil sample NH4-N concentrations (mg kg-1) at perched water table for ‘Atlantic’ potato when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006. ............................................................................ 91
4-8 The soil sample NO3-N concentrations (mg kg-1) at perched water table for ‘Atlantic’ potato when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006. ............................................................................ 92
5-1 Fertilizer formulation, manufacturer, nitrogen form, and water solubility........... 122
5-2 Fertilizer treatments for potatoes grown under traditional and alternative fertilizer programs from Hastings, FL in 2007, 2008 and 2009. ........................ 122
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5-3 Influence of fertilizer source and timing of application on ‘Atlantic’ tuber yield and specific gravity when grown in Hastings, FL during 2007. ......................... 123
5-4 Influence of fertilizer source and timing of application on ‘Atlantic’ tuber yield and specific gravity when grown in Hastings, FL during 2008. ......................... 123
5-5 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Atlantic’ potatoes from Hastings, FL during 2007............ 124
5-6 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Atlantic’ potatoes from Hastings, FL during 2008............ 125
5-7 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘Atlantic’ potato grown with different fertilizer treatments from Hastings, FL during 2007. ........................... 126
5-8 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) for ‘Atlantic’ potato grown with different fertilizer treatments from Hastings, FL during 2008....................................................................................................... 126
5-9 Influence of fertilizer source and timing of application on ‘Harley Blackwell’ tuber yield and specific gravity when grown in Hastings, FL during 2007......... 127
5-10 Influence of fertilizer source and timing of application on ‘Harley Blackwell’ tuber yield and specific gravity when grown in Hastings, FL during 2008......... 127
5-11 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Harley Blackwell’ potatoes from Hastings, FL during 2007. ................................................................................................................ 128
5-12 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Harley Blackwell’ potatoes from Hastings, FL during 2008. ................................................................................................................ 129
5-13 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘Harley Blackwell’ potato grown with different fertilizer treatments from Hastings during 2007. ............... 130
5-14 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘Harley Blackwell’ potato grown with different fertilizer treatments from Hastings during 2008. ............... 130
5-15 Influence of fertilizer source and timing of application on ‘FL 2053’ tuber yield and specific gravity when grown in Hastings, FL during 2007. ......................... 131
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5-16 Influence of fertilizer source and timing of application on ‘FL 2053’ tuber yield and specific gravity when grown in Hastings, FL during 2008. ......................... 131
5-17 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25 cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘FL 2053’ potatoes from Hastings, FL during 2007. ......... 132
5-18 Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25 cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘FL 2053’ potatoes from Hastings, FL during 2008. ......... 133
5-19 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25 cm and full-flower growth stage for ‘FL 2053’ potato grown with different fertilizer treatments from Hastings, FL during 2007. ........................... 134
5-20 Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘FL 2053’ potato grown with different fertilizer treatments from Hastings, FL during 2007. ........................... 134
6-1 Fertilizer formulation, manufacturer, nitrogen form, and water solubility........... 149
6-2 Tuber yield, size distribution and specific gravity for potato cultivar ‘Atlantic’ grown with differing fertilizer treatments and under a natural and simulated rainfalls (5 cm) at the University of Florida Hastings farm, FL in 2008.............. 149
6-3 External and internal defects for potato 'Atlantic' cultivar grown under several fertilizer treatments and under natural and simulated rainfalls (5 cm) at University of Florida Hastings farm, FL in 2008. ............................................... 150
6-4 In-row leachate NH4-N, NO3-N and total Kjeldahl N (TKN) concentration and N leaching from several fertilizer treatments after a natural 5 cm rainfall at potato 20-25 cm growth stage at University of Florida farm in Hasting, FL in 2008. ................................................................................................................ 150
6-5 n-row leachate NH4-N, NO3-N and total Kjeldahl N (TKN) concentration and N leaching from several fertilizer treatments after a simulated 5 cm rainfall at potato full flower growth stage at University of Florida farm in Hasting, FL in 2008. ................................................................................................................ 151
6-6 Soil sample NH4-N and NO3-N concentration after a natural and simulated 5 cm rainfall at the University of Florida Farm in Hastings, FL in 2008................ 151
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LIST OF FIGURES
Figure page 3-1 The cumulative nitrogen release (CNR) expressed as percentage of total
available N (TAN) at the day 91 associated with temperature for each CRF under the temperature controlled system. .......................................................... 60
3-2 The asymptote for a Gompertz model (a) of each fertilizer associated with temperature. ....................................................................................................... 61
3-3 The growth rate from a Gompertz model (c) for each CRF associated with the temperature. ................................................................................................. 61
3-4 The estimate days for 25% release of total available nitrogen (LD 25) for each CRF associated with temperature.............................................................. 62
3-5 The estimate days to reach 50% release of total available nitrogen (LD 50) for each CRF associated with temperature. ....................................................... 62
3-6 CNR release curve of each CRF at variable temperature setting over the duration of the incubator experiment .................................................................. 63
3-7 The linear relationship of release parameter of PCUs and temperature of the incubator experiment .......................................................................................... 64
3-8 Comparion of PCU the actual release and calucated release of PCU under variable temperature over the duration of the incubator experiment................... 66
4-1 Average daily 60 cm air temperature(C°), 10 cm depth soil temperature (C°) and daily rainfall (cm) during growth season in Hastings, FL, in 2006................ 93
5-1 Average daily temperature (60cm air temperature and 10 cm soil temperature) and daily rainfall (cm) during growing seasons (from planting to harvest) ............................................................................................................ 135
5-2 NH4-N and NO3-N concentrations in the perched ground water after the last fertilization averaged over fertilizer treatment ................................................... 136
6-1 Daily rainfall (cm) and average daily air temperature (60 cm) and soil temperature (10 cm depth) at University of Florida Hasting farm, FL in 2008 .. 152
6-2 Lysimeter in the field and experiment design ................................................... 153
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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy
AVAILABILITY, EFFICIENCY, AND FATE OF ALTERNATIVE NITROGEN SOURCES
IN SEEPAGE IRRIGATED POTATO PRODUCTION
By
Zhiwei Chen
August 2010
Chair: Daniel Cantliffe Major: Horticultural Science
Vegetable crop production in the Tri-County Agricultural Area (TCAA) consisted of
approximately 11330 ha irrigated vegetable cropland predominated by cabbage (2n =
18; Brassica oleracea L.) and potato (2n = 48; Solanum tuberosum L.) crops. The
current nutrient losses associated with agriculture system are due to combined factors
such as sandy soils, perched water tables, and unpredictable rainfall. Also, high
fertilization rate is a concern for future sustainable development and environmental
quality. Best Management Practices (BMPs) have been implemented in the TCAA to
help growers apply alternative agricultural practices to remain profitable while reducing
the negative impact of environmental quality, especially water quality.
The controlled-release fertilizers (CRF), as one potential component of BMPs,
were evaluated for their influence on potato production, tuber quality, and water quality.
The research objectives were to: 1) characterize a nutrient release profile of CRFs
under laboratory and field conditions; 2) determine the influence of CRF programs on
potato production, tuber quality and water quality; 3) compare nutrient use efficiency of
several fertilizer programs and; 4) estimate in-row soil nutrient movement of several
fertilizer programs for northeast Florida potato production.
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This research was divided into three sub-experiments: CRF evaluation under a
controlled system, field evaluation of CRF, and a nutrient in-row movement study.
Release profiles of several fertilizer sources were evaluated under controlled constant
and variable temperature. P-PSCU (polymer sulfur-coated urea, 420 g N kg-1, Purcell
Technologies, INC) and H-PCU2 (polymer coated urea, 420 g N kg-1, Haifa Chemical,
LTD) were potential fertilizer candidates to synchronize the N demand of potato crop at
northeast Florida production. The linear formula (K=AT+B) developed in this study
described the relationship directly between release rate (K) and temperature (T), where
A and B are constants. The protocols of CRF evaluation developed from this study can
successfully determine the fertilizer release profile prior to field application.
The field study evaluated alternative fertilizer program and potato cultivars on
tuber production, tuber quality, and ground water quality. The results from CRF field
evaluations demonstrated that PSCU (380 g N kg-1, Scotts LLC) and PCU (440 g N kg-1,
Agrium INC) led to comparable total and marketable yields as compared to soluble N
fertilizers. For ‘Atlantic’ and ‘FL 2053’, tuber yields were higher for plants fertilized with
PSCU applied before and at planting or a PCU combination with AN sidedress
compared to other fertilizer program. For ‘Harley Blackwell’, tuber yields were similar
between different treatments, indicating more flexibility of fertilizer application. Though
yields were lower, ‘Harley Blackwell’ and ‘FL 2053’ had greater resistance to tuber
internal heat necrosis (IHN), a psychological disorder than ‘Atlantic’. Plants fertilized
with a liquid CRF program (urea formaldehyde) produced significantly lower total and
marketable yields due to their slow release characteristics than plants with the AN
treatment.
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The nutrient in-row movement study demonstrated that plants fertilized with
polymer sulfur-coated urea (PSCU, 380 g N kg-1, Scott LLC) or polymer coated urea
(PCU, 440 g N kg-1, Agrium INC) produced higher total and marketable yields than
plants fertilized with urea formaldehyde (UF) products under leaching events. Leaching
water samples collected from plots fertilized with PSCU had the highest NO3-N
concentration and loads (24.4 mg L-1 and 12.4 kg ha-1) since N release of PSCU was
less temperature sensitive resulting in high N release in the early season. These results
would support the use of PCU over PSCU as a CRF. A 5 cm rainfall at early growth
(20-25 cm) and full-flower growth stages reduced soil NO3-N concentration below the
sufficient range (tuber initiation: greater than 20 mg kg-1; tuber bulking: 15~20 mg kg-1),
resulting in yield losses. This indicated that plants fertilized with CRFs at 196 kg N ha-1
with two potential leaching events during growing season required supplemental N to
avoid yield losses during a 100 day growth season.
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CHAPTER 1 INTRODUCTION
In Florida, potatoes (Solanum tuberosum L.) grown for fresh market or chipping
industry have a value in excess of $163 million (USDA, 2007). Most of the 10,610 ha in
potato production are located in the Tri-County Agricultural Area (TCAA) composed by
St. Johns, Putnam, and Flagler Counties, which represents 60% of Florida annual
potato production (USDA, 2007).
The requirement for high nutrient input for optimum potato production increases
the potential for nutrient losses (Milburn et al., 1990; Honisch et al., 2002). Growers
tend to apply high N rate as an inexpensive insurance to hedge against potential
nutrient losses, sometimes resulting in low nutrient use efficiency (Zotarelli, 2007).
Nutrient losses have become a major concern for agricultural sustainable development
and environmental quality, especially water quality. In Florida, after the passage of the
Federal Clean Water Quality Act of 1977, the Florida Surface Water Improvement and
Management (SWIM) Act was established in 1987 by the Florida legislature aimed to
reduce non-point source of pollution on surface and ground water. The Florida water
management districts partners with appropriate state, local, and regional agencies to
preserve and/or restore of the state's water bodies through the development and
implementation of surface water improvement and management plans and programs.
Best Management Practices (BMPs) are part of the programs to assist growers to
maintain or increase economical yields while reducing the load of a specific compound
in to water. The agricultural BMPs apply the technology and practical experience of
professionals to manage irrigation, fertilization, and pest control to balance economical
vegetable production with environmental responsibility (Hochmuch and Simonne, 2009).
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Fertilizer management and rates for vegetable production are major components
of Florida BMPs. In the TCAA production area, potatoes are grown in sandy, coarse
texture soils irrigated by a sub-surface seepage system. Beside low water use
efficiency, seepage irrigation is vulnerable to nutrient losses especially N due to the
continuous irrigation with open beds and potential of heavy rainfall (Munoz et al., 2007).
Potatoes have a relatively shallow root system, resulting in a low water/nutrient holding
capacity at the root level. These factors promote nutrient losses, especially N under
intensive rainfall. NO3-N leaching or run off can result in subsequent pollution of various
water bodies. Most soil N is converted into the NO3-N after fertilizer application. This
process can be rapid under warm growing conditions, such as Florida (Jansson and
Persson, 1982). In order to reduce NO3-N movement from potato production in the St.
John’s River watershed, BMPs have been developed. Potato growers that participate in
BMP programs can apply a N rate up to 224 kg ha-1 (Hochmuth and Hanlon, 2000) with
additional supplemental in row applications of up to two 34 kg N ha-1 if a leaching rain
occurs (defined as 7.6 cm in 3 days or 10cm in 7 days) (Kidder et al., 1992).
A major challenge in crop management is to synchronize fertilizer application to
crop nutrient demand while reducing nutrient losses (Tilman et al., 2002). Application of
fertilizer at a late growth stage is generally limited in TCAA seepage-irrigated potato
production when plant canopy is well development. CRFs are formulated to slowly
release a nutrient over time which may reduce nutrient losses by releasing nutrients
slowly so that plants may use them as released. Potato plants generally take up the
majority of N at tuber initiation and tuber bulking stages (Westermann, 1993). The
appropriate CRF programs may be one important potential component of a BMP
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program to achieve both production and environmental goals. With slow release
characteristics to synchronize plant nutrient demand, CRF programs may improve
potato tuber yield and quality, reduce application times, and minimize excessive NO3-N
leaching.
However, the high cost per unit of nutrient has been a primary factor that have
limited wide acceptance of CRF application (Trenkel, 1997; Zvomuya and Rosen,
2001). Beside the high cost, the difficulties to predict nutrient release of CRF under
variable field conditions limits their commercial use. Manufacturers formulate CRFs
using different materials and release mechanisms without providing sufficient
information that states release characteristics or timing under field conditions. Also, if
the CRFs are not able to release N rapidly enough, reduce yields can ensure (Guertal,
2009). It is important to investigate the release patterns with construction of
mathematical models for predicting release rate of CRFs, provide improvement of
optimal design of CRF compositions, and determine the appropriate application
program such as N source, N rate, and application timing before commercial use.
This research was conducted to evaluate the potential of controlled-release
fertilizer (CRF) application for optimizing Florida potato production and environmental
quality. Plants fertilized with CRFs have been reported to produce comparable yields for
potato production as traditional fertilizer program with reduced N losses to the
environment (Zvomuya and Rosen, 2001; Hutchinson and Simmonne, 2001; Pack et al.
2006). The release rate, pattern, and duration may also be strongly affected by
environmental conditions and soil properties (Shaviv, 2000). The greater variance of
nutrient release from CRFs increases the risks of yield losses or reduction in tuber
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quality. Appropriate CRFs management programs are still under development in term of
N rate, source, and application programs for Florida potato production. A successful
CRF program for vegetable production requires a predictable pattern for nutrient release
in order for the CRF to be customized for individual crop growth and development
stages (Worthington et al., 2007).
To achieve this goal, several experiments were conducted with the objectives of: i)
characterizing the release profile of CRFs associated with temperature, developing a
prediction model to simulate release rate under field conditions and determining fertilizer
candidates for subsequent evaluation in Florida potato production; ii) determining the
appropriate fertilizer source and optimum N and influence of CRFs on perched water
table quality; iii) evaluation of the optimum application program through field evaluation;
iv) evaluating the influence of CRFs on reducing in row nutrient losses under potential
leaching events.
The results of this research will provide a comparison between CRF and traditional
fertilizer programs to potato growers, assist fertilizer manufacturers to develop
improvements of CRF formulation for Florida potato production, establish the release
prediction model to quantify N release of CRFs under variable condition, and provide
data to direct appropriate CRF application program in future research.
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CHAPTER 2 LITERATURE REVIEW
Potato (Solanum tuberosum L.) is considered as one of the important food sources
and ranked as the fourth most important food crop after wheat, corn and rice (Rowe,
1993). The popularity of potato is mainly attributed to its ability to readily adapt to
temperate growing conditions and provide greater nutrition on smaller land areas than
most other crops. Scientists continue to look for new agricultural practices to improve
potato tuber yields and quality for sustainable development while protecting the
environmental quality.
Potato plant growth requires additional nutrient inputs for high yields and quality
besides residual nutrients in the soils. Addition of fertilizer provides sufficient nutrients
for a uniform and healthy potato plant growth. Application methods have included
addition of organic fertilizer, various soluble or slowly soluble fertilizer forms and coated
fertilizers. The appropriate fertilization management for production may vary upon local
agricultural factors such as soil structure, soil pH, climate, cultivar nutrient profiles, etc.
This review will discuss the importance of potato nutrient management, mainly nitrogen
(N), in northeast Florida for potato production and tuber quality associated with its
influence on the environmental quality.
Potato Nitrogen Management
Nitrogen (N) is a major component that impacts potato yield and quality
(Westermann, 2005). Nitrogen is the primary component of all nucleic acids, proteins,
and amino acids and is also a component of cell protoplasm, chlorophyll, nucleic acids,
and enzymes (Thompson, 1999). Nitrogen fertilization of potatoes has become highly
specialized with specific applications for a given set of conditions. Nitrogen can be taken
20
up by plants as nitrate (NO3-) or ammonium (NH4
+). Potato plants generally take up the
NO3- form through the water into roots from conversion of NH4
+ to NO3- in the soil
(Gardner et al., 1985). Previous research has indicated that the NO3-N is a more
appropriate N form for potato growth than the NH4-N. For example, Polizotto et al.
(1975) reported when ‘Red Pontiac’ and PU 66-142 potatoes were cultured in solution,
the growth of tops, roots, and tubers was greatest with N supplied as NO3, intermediate
with NH4 + NO3, and least with NH4. Davis et al. (1986) reported that changing the N
source from NO3 or NH4 + NO3 to NH4 reduced both shoot and root growth while
changing the N source from NH4 to NH4 + NO3 improved growth for ‘Russet Burbank’
potatoes. Therefore, a certain amount of NO3-N needs be available for proper potato
growth and if NH4-N was the sole form of N available to the plant, it was detrimental to
potato growth, regardless of stage of plant development (Davis et al., 1986).
Though approximately 78% of N in the environment occurs as dinitrogen (N2) in
the atmosphere, it is unavailable to most of the higher plants since they are unable to fix
N2. Commercial fertilizer can be applied to potato crops as a sidedress after planting to
increase potato crop yields in most soils. Nitrogen exists in commercial fertilizers in
different forms including nitrate nitrogen, ammonium nitrogen, water soluble organic N,
and water insoluble N. However, N requirement by a potato crop depends primarily on
the length of the growing season, climate, soil type, rainfall and the cultivar being grown
(Westermann, 1993). The appropriate N management is very important to maintain the
proper potato plant growth. The potato life cycle can be divided into five general growth
stages as: sprout development, vegetative growth, tuber initiation, tuber bulking, and
maturation (Rowe, 1993). The different metabolic activities of a potato plant in each
21
growth stage may result in different N requirements. Early in the growing cycle, potato
plants have a relatively low N requirement. The N requirement increases slightly during
tuber initiation stage, with the highest N requirement occurring at the tuber bulking stage
(Ojala et al., 1990). Plant vegetative growth must be well established before this occurs.
Adequate N promotes uniform and continuous growth of plants and tubers
throughout all growth stages. Likewise, it may help suppress the development of some
diseases such as early blight and its associated yield loss (Huber, 1990). However,
heavy applications of N may cause undesired plant growth such as excessive
vegetative growth. Excessive vegetative growth due to over application of N may delay
tuber bulking resulting in lower yield (Westermann and Davis, 1992). Some tuber
characteristics, such as low specific gravity and high tuber NO3-N concentration are
more prevalent when fertilization exceeds the N requirement for normal growth
(Belanger et al., 2002). Specific gravity (SG), an indirect method to determine dry matter
or starch content in a tuber, is an important quality characteristic for the processing
industry (Iritani and Weller, 1980). Processors pay a premium for potatoes with high
specific gravity because they produce higher quality chips. Advantages of high SG
include more processed product per unit of raw product used, less oil absorption during
frying, a shorter frying time, and less reducing sugars accumulated in storage as
compared to low specific gravity tubers (Harris, 1978; Irritani and Weller, 1973; Smith,
1976). Potatoes with high specific gravity generally produce higher color quality chips
since they accumulate less reducing sugars during low-temperature storage (Iritani and
Weller, 1980). Another problem with excess N application, especially in the late growing
stage is the accumulation of high sugar content in the tuber where excessive N can
22
prolong vegetative growth and delay tuber chemical maturity (Belanger et al., 2002).
Immature tubers not only have poor processing quality with dark color at harvest but
also are not favored by the processing industry because they accumulate greater
amounts of reducing sugars in storage (Iritani and Weller, 1980). Therefore, inadequate
or over fertilization during tuber initiation and bulking stages may cause some tuber
malformations including knobby tubers, where lateral growth of buds has occurred, and
growth cracks or splits in the outer flesh and skin of the tuber (Ojala, 1988). Growers
may over apply fertilizer hedging the potential risk of nutrient loss. Excessive nutrients
above plant needs lead to the risk of loss due to leaching or run off under heavy rainfall.
In conclusion, appropriate N management is important for high yield, optimum quality
tubers with minimal on environmental quality.
Monitor Potato N Status
Monitoring of N status in a potato crop can help guide fertilizer N management
during the growing season. There are several methods which have been developed to
help assess potato crop N status.
Testing of petiole NO3-N concentration is a simple method to measure N
sufficiency. Petiole sap analysis for NO3 levels is a particularly effective technique to
monitor N for potato production since the petiole is a good indicator of soil N supply.
Potato growers can adjust management practices such as supplemental N application
through irrigation systems with petiole N analysis results when deficiencies or excesses
are detected. In a two-year study, Westcott (1993) reported that there was a consistent
relationship between petiole sap NO3-N concentration and dry matter NO3-N
concentration in potatoes. A previous study reported that petiole NO3-N concentrations
were affected by both plant age and amount of N fertilizer applied (Gardner and Jones,
23
1975). Lewis and Love (1994) reported that given the same N level in the soil, potato
genotypes differ in petiole NO3-N concentrations over time. Monitoring petiole NO3-N
throughout the growing season can be used as an indirect measurement of soil N
availability and other factors influencing plant N uptake, growth, and yield (Westcott et
al., 1991). Therefore, petiole N analysis will help to understand the N uptake profile of
particular potatoes variety, especially in new cultivars.
The crop N nutrient index (NNI) is the ratio of measured N concentration in leaf for
any given quantity of crop biomass to critical N curves (Greenwood et al., 1990). The
critical N curves have been developed for potato with biomass including vine and tubers
(Belanger et al., 2001). Therefore, the N concentration in tissues (leaf, stem and tuber)
at critical growth stages can be used to determine the N fate or distribution in plants
during the growth season.
Another method to measure potato crop N status is to measure N supply in the
soil. The in-season soil nitrate test has been suggested to be used to monitor the N
supply because of the potential loss of residual N after a previous crop season
(Belanger et al., 2001). The in season soil N measure soil NO3-N concentration within
the hill (Belanger et al., 2001) or surface soil (Rodrigues, 2004) to calculate if additional
fertilizer N is required for a proper potato growth. Late season soil NO3-N measurement
provides soil N status in the later season after the contribution from soil N mineralization
early in the growing season has occurred. Therefore, assumed a limited in-season
nitrate leaching, the post-harvest soil NO3-N test measures residual soil nitrate in the
root zone after a crop harvest. This can be used to determine whether crop N supply
exceeded crop N demand. However, determination of both nitrate and ammonium
24
concentration would be required to assess soil N supply for high N rates because of the
inhibition of nitrification results in significant high concentrations of soil ammonium
(Zebarth and Milburn, 2003).
The optical methods are also used as an indirectly method to measure the potato
crop N status. The optical methods are based on the quantification of leaf chlorophyll
content since chlorophyll contents are often correlated with leaf N concentration. Among
current available optical devices for measuring N status, the SPAD-502 meter is the
most commonly used optical method for potato (Vos and Bom, 1993; Minotti et al.,
1994). Compared to the petiole NO3-N concentration, leaf chlorophyll measurement is
able to assess the crop N status over a wider time frame (Zebrath and Rosen, 2007).
Therefore, the chlorophyll meter was very useful to determine the supplemental N
requirements for potato (Olivier et al., 2006).
In all the direct or indirect in-season N status monitor provides a guide for fertilizer
management. The appropriate fertilizer supplement would match up with N demand of a
potato crop and improve environmental quality, especially water quality.
The TCAA Production Area
The agricultural production area from Palatka to south of Orange Park along the
eastern shoreline contains Putnam, St. Johns, and Flagler countries is commonly
known as the Tri-County Agricultural Area (TCAA). The TCAA production consists of
primarily potato, cabbage and other cole crops. Potato acreage is estimated 67% of the
row crop hectares in TCAA. The growing season starts in the late December or early
January through late May or early June. After harvest, cover crops such as sudan
sorghum are generally planted to prevent the wind and water erosion.
25
The soils in the TCAA production areas are sandy and loamy soils with an
underlying impermeable layer within approximately 0.3 to 0.5 meters of the soil surface
(Livingston-Way, 2007). Most soils where potatoes are grown in Florida are sandy with
low water holding capacity (1.9 cm per 30 cm soil) (Hutchinson et al., 2002a). With a
high water infiltration rate, sub-surface irrigation is commonly used in TCAA production
to provide soil moisture during the growing season with a perched water table at 45 to
60cm depth. Sub-surface irrigation, irrigates 16 rows (hill height 0.2-0.36 m) between
each water furrow. Potato plants have a shallow root system with the poor feeding
capacity for nutrients. Munoz (2004) has reported from a potato root distribution study in
northeast Florida that more than 90% of the total root area is located in the upper 25 cm
of the soil profile. The nutrients, specifically N, have high potential risk of leaching in
heavy rainfall due to the sandy soils, resulting in nutrient moving into surface water.
Previous study indicated that 70% of the accountable N was removal through biomass
removal, and 22% was lost through surface water runoff (Livingston-Way, 2007).
Therefore, alternative management practices must be considered for nutrient load
reduction.
Florida Best Management Practices
The Florida Surface Water Improvement and Management (SWIM) Act was
passed in 1987 to address water quality issue, restore degraded lakes, rivers, streams,
estuaries and bays, and preserve the quality of more pristine water bodies (Northeast
Florida Water Management District, 2009). The SWIM program has focused primarily
on water resource and quality preservation and restoration of the state's water bodies
through the development and implementation of Best Management Practices (BMP)
(Simonne et al., 2003).
26
Agricultural BMPs are scientifically-based cultural farming practices that should
maintain profitability while protecting the environment (Simonne et al., 2003). The lower
St. Johns River basin encompasses the TCAA. The TCAA contains approximately
11,330 hectares of agricultural croplands, which could generate large quantities of
sediment and nutrient-enriched agricultural run off if not managed properly (Livingston-
Way, 2007). A study conducted by Hendrickson et al. (2007) indicated that agricultural
productions as the major anthropogenic source of pollution, contributed to 50% and
39% of the bioavailable P and N augmented nonpoint source load, respectively, to the
freshwater laucustrine zone of the lower St. Johns River. The BMP program is part of
the TCAA Water Quality Protection Cost Share Program managed by the St. Johns
River Water Management District (SJRWMD) (Livingston-Way, 2002). For local
agricultural crop growers, the BMP programs target to implement the alternative
practice reducing potential pollution to environmental quality, especially water quality.
The BMP implementation on 90% of row crop lands in the TCAA aims to achieve a 39%
reduction in the N load and a 19% reduction in the P load (Livingston-Way, 2007).
Implementation of BMPs applies the technology and practical experience of
professionals to manage irrigation, fertilization, pest management in a manner
minimizing environmental impact while remaining a growers’ profit. Potato growers in
the TCAA tend to apply N hedging for the potential risk of loss with average N rate at
280 kg N ha-1, ranging from 195 kg N ha-1 on fresh market potato to 390 kg N ha-1 for
some chipping potatoes (Pack, 2004). However, the base N rate of BMP adopted from
the University of Florida’s Institute of Food and Agricultural Science (IFAS)
recommended rate was 224 kg N ha-1, with the possibility to sidedress up to two 34 kg
27
N ha-1 under leaching rain (Hochmuth et al., 2003). Proper N application timing is also
very important to maximize potato yield and to improve tuber quality. Westermann
(1993) divided potato growth into five growth stages: sprouting, vegetative, tuber
initiation, tuber bulking and maturation. The length of each growth stage differs with
genotypes, soil type and environmental conditions. At each growth stage, potato crops
have different N requirement. Generally, the majority of N is not taken up by potato at at
the early stages or at maturation but at tuber initiation and tuber bulking stages
(Westermann, 1993). Based on the potato N uptaken profile, a split N application is
suggested by IFAS for potato production for greater N use efficiency. Errebhi (1998)
reported that as the percentage of total N applied pre-plant increased, the total
marketable yield decreased, even though total yields remained the same when “Russet
Burbank” potatoes were grown on a sandy loam soil in Minnesota. In their study, they
also reported that split applications of N fertilizer reduced nitrate leaching and increased
N recovery. However, to improve tuber maturity at harvest, fertilizer applications,
especially N, should be terminated from two to six weeks before the start of the
maturation stage, depending on the specific cultivar and growing conditions (Ojala et al.,
1990; Westermann, 1993). In Florida potato production, UF/IFAS recommended that
growers should apply approximately 30% of the total N at planting and the remainder
banded 35-40 days after planting. Nitrogen rates should be based on plant nutrient
status analysis. The cultural practices in Florida potato production also require
fumigation every year to reduce disease pressure. An alternative fertilizer practice may
use a certain percentage controlled release fertilizer (CRF) of total nutrient at soil
fumigation timing. Soil fumigation reduces microbial activity which may delay nutrient
28
release from CRFs (Morgan et al., 2009). Microbial activity recovers several weeks after
soil fumigation, which may increase the N release rate. The delayed release of CRFs
applied at fumigation timing may match nutrient demand of potato plants in early stages
of development. UF/IFAS also recommended installation and monitoring of water table
observation wells, control structures to trap sediment from the field, and conservation
crop rotations (Hutchinson et al., 2002 a). Appropriate placement of N fertilizer is also
very important to improve N use efficiency especially for Florida sandy soils. Banding
fertilizer practices place nutrients in a region more accessible to plant roots as
compared with broadcasting. Malik (1995) reported that nutrient concentrations were
less around potato root systems when fertilizer was broadcast than banded.
Westermann and Sojka (1996) reported that banding N increased average plant dry
weight 6.4%, total tuber yield 9%, and N uptake 28% as compared with broadcast N for
‘Russet Burbank’ potato production.
Controlled-release Fertilizer
Controlled-release fertilizers (CRFs) are formulated to release nutrient in quantities
more slowly over time (Pack et al., 2006). Currently, most controlled-release fertilizer
usage is limited in non-farm such as lawns and high value crops. Increased pressure
from environmental regulatory agencies and the adoption of Best Management
Practices (BMP’s) are pushing for more controlled-release fertilizer sources into the
market. The terms controlled-release and slow-release are used interchangeably
without a real physical difference in the two products (Sartain, 2006). Sartain (2004)
stated that controlled-release products refer to materials that have been manufactured
in such a method to control nutrient element release, while the slow-release products
29
are those which release the nutrient element over time due to the physical nature of the
material.
Most of the controlled-release products in research or commercial market are N
controlled release products. Controlled-release N fertilizers can be categorized as either
N reaction products or N coated product (Sartain, 2006). Nitrogen reaction products are
produced by the chemical reaction of water-soluble N compounds to create N fertilizers
possessing more complex molecular structures which result in limited water solubility,
such as urea-formaldehyde. Coated N fertilizers limit fertilizer availability by a water-
insoluble barrier which blocks access of water to fertilizer for dissolution, such as sulfur-
coated urea, polymer-coated urea, and polymer sulfur coated urea. Controlled-release
fertilizer products which are currently produced will be discussed. CRFs reduce N
leaching either by limiting the solubility and availability or by limiting the conversion to
mobile forms of N.
Urea-Formaldehyde Reaction Nitrogen Products (UFs)
Urea-formaldehyde reaction products were first commercialized in 1955 under the
trade names of uramite and nitroform. These CRFs, referred to as methylene ureas, are
products that result in a distribution of methylene urea (MU) polymers of varying
molecular weights or polymer chain lengths and of varying water solubility (Sartain,
2006).
The release mechanism includes dissolution and decomposition, slowly releasing
into the soil solution by virtue of low solubility. Once in the soil solution, UF reaction
products are converted into plant available N through microbial decomposition or
hydrolysis (Sartain, 2006). Carbon in the methylene urea polymers provides a site for
microbial activity. Since microbial decomposition is the primary mechanism of N
30
release, the environmental factors which affect the microbial decomposition also affect
N availability of UF products. The rate of N release from a UF reaction product might
vary due to the length of polymer chain when they are manufactured. The approximate
length of UFs would ensure the availability of N released to match up with the N
demand of plant growth in a specific production environment.
Urea-formaldehyde products are commercially available as granular and liquid
products. Granular products can be divided into three classes: ureaform, methylene
ureas, and methylene diurea (MDU)/dimethylene triurea (DMTU) while the liquid UFs
can be divided into two groups as water suspensions and water solutions based on the
degree of water solubility. The UFs also contain unreacted urea with the lowest
molecular-weight distribution (shorter polymer chain length) containing the highest
amount of unreacted urea N.
Sulfur-Coated Nitrogen Products (SCU)
Sulfur-coated urea technology (SCU) was developed in the 1960’s and 1970’s by
the Tennessee Valley Authority. Advantages of SCU are, its coating material is low cost
and sulfur can be used by plants as a secondary nutrient. However, the imperfections in
the sulfur coating is a common problem that now most manufactures use soft sealants
as a secondary coating over the sulfur coating in order to provide the handling integrity
and fill the imperfections (Sartin, 2006). The N release mechanism of SCU is via water
penetration through micropores and imperfections. If the soft sealant is also applied,
then microbes in the soil environment must digest the sealant to reveal imperfections in
the sulfur-coating to create a dual release mechanism (Sartin, 2006). Therefore, the
nutrient release of the wax-sealed SCUs is related to temperature because it regulates
the microbial growth.
31
Although SCUs are lower in cost, N release did not sychronize with most crop N
demand during the growth season (Maynard and Lorenz, 1979; Elkashif and Locascio,
1983). For example, Lorenz et al. (1972, 1974) reported that ammonium sulfate was
generally superior to SCU or urea-formaldehyde (a slowly available N source) for ‘White
Rose’ potatoes in the studies conducted over several years in three locations in
California. Cox and Addiscott (1976) demonstrated that potato tuber yields were greater
for plants treated with ammonium nitrate than for SCU for rates up to 200 kg N ha-1 on
‘King Edward’ potatoes in Rothamsted, England. Elkashif et al. (1983) reported similar
results in Florida where yields of ‘Atlantic’ potatoes grown on two sandy soils fertilized
with SCU or a SCU/ammonium nitrate (AN) blend were lower than treatments with only
AN. Potato yields were similar for rates from 134 to 201 kg N ha-1 either as preplant or
split applications. In central Minnesota, Waddell et al. (1999) reported that ‘Russet
Burbank’ plants on a sandy loam soil treated with SCU at a N rate of 224 kg N ha-1
produced lower tuber yields than urea under either drip or sprinkler irrigation. Lower
yields were obtained with SCU treatments due to slow availability of N from the SCU
product during entire the growing season. In summary, lower yield performance of
plants treated with SCUs were attributed to incomplete or too slow release of N from
SCUs over the season.
Polymer-Coated Nitrogen Products (PCUs)
Polymer-coated fertilizers are a type of CRF with the most advanced technology in
terms of a controlling mechanism for nutrient release. Most polymer-coated fertilizers
release by the mechanism of diffusion through a semipermeable membrane. The
polymer coatings are relatively high cost materials either made from thermoset resins or
thermoplastic resins, resulting in the higher cost. The rate of N release can be altered
32
by composition of the coating or the coating thickness in order to best synchronize N
demand. Although water diffusion is required, speed of nutrient release from the prill is
primarily affected by soil temperature and not moisture (Gandeza et al., 1991). Maeda
(1990) evaluated various soil factors affecting N release and reported that temperature
accounted for about 83%, soil moisture accounted 11%, and other soil factors such as
microbial activity and pH and their interactions each accounted for less than 1% of the
release rate. Only when soil moisture was less than the plant wilting point (10 kPa), did
soil moisture become the primary controlling factor in nutrient release speed (Fujita et
al. 1983 and Fujita, 1989). Dry soil conditions limits diffusion of nutrients away from the
prill. The high correlation between nutrient release speed and change in soil
temperature allows for dependable prediction of nutrient release in temperature
controlled systems.
Zvomuya and Rosen (2001) reported that ‘Russet Burbank’ potatoes treated with
PCU (applied at planting) on a sandy soil in Minnesota produced higher marketable
yields than a urea treatment (applied at emergence and hilling) for application rates
ranging from 110 to 290 kg N ha-1. In later studies, Zvomuya et al. (2003) reported that
at 280 kg N ha-1, NO3-N leaching was 34 to 49% lower with PCU treatments than three
split applications of urea, while N recovery efficiency (NRE) for PCU averaged 50%, 7%
higher than urea treatments (43%). Shoji et al. (2001) demonstrated that PCU could
markedly increase N use efficiency (NUE) and tuber yields of ‘Centennial’ russet
potatoes. They also reported that plant NUE values of CRF products were nearly
doubled compared to that of urea N. These results were attributed to the ability of CRF
products to supply N synchronously with plant requirements. In northeast Florida on
33
‘Atlantic’ potatoes, Chen et al. (2008) also reported that plants grown with PCU as the N
source produced similar total and marketable yield for ‘Atlantic’ potato at reduce N rate
(196 kg N ha-1) as compared to AN treatment at 224 kg N ha-1.
In summary, PCUs have shown promising results leading to the similar total and
marketable yields because of their higher nutrient use efficiency as compared to a
traditional fertilizer program. Release of N from PCU is primarily dependant on soil
temperature.
Polymer/sulfur-Coated Nitrogen Products (PSCU)
Polymer/sulfur coated ureas are hybrid products that utilize a primary coating of
sulfur and a secondary polymer coat. PSCUs aim to deliver a similar controlled release
of N as a PCU but at lower cost because the primary coating, sulfur, is relatively
inexpensive. A low level of polymer is used to provide a continuous membrane that
water and nutrients diffuse through in order to achieve a controlled release
performance. The nutrient release mechanism is through a combination of diffusion and
capillary actions. Water vapor first diffuses through a continuous polymeric membrane
layer. Then, water subsequently penetrates the defects in the sulfur coat through
capillary action and solubilizes the fertilizer cores. Soluble nutrients then can exit the
particle in reverse sequences. With the combined mechanism, the PSCUs are expect to
provide greater uniformity in nutrient release as compared to the SCU and release
nutrients from a less temperature sensitive particle than most PCUs (Sartain, 2006).
In northeast Florida on ‘Atlantic’ potatoes, Chen et al. (2008) reported that plants
treated with PSCU treatments with flexible application timing (at planting, supplemental
at hilling or split) produced similar total and marketable yield for ‘Atlantic’ potato at a
reduce N rate (196 kg N ha-1) as compared to AN treatment at 224 kg N ha-1. Use of
34
PSCU has also been reported to improve potato tuber inner quality because of
improved synchronizing the N demand of potato during the growing season. Hutchinson
(2005) reported use of PSCU at 168 kg N ha-1 had a 69% reduction internal heat
necrosis (IHN)) as compared with a standard AN based fertilizer program. Pack (2004)
also reported that in a northeast Florida potato production study that an average
reduction of 68% of tubers with IHN was found when grown with PSCU compared to a
standard AN based fertilizer program (50%-50% N split applications at planting and
hilling) .
Urea-Other Aldehyde Reaction Products
The two popular products from the urea reaction with other aldehydes are
isobutylidene diurea (IBDU) and crotonylidene diurea (CDU). The IBDU is the
condensation production of urea and isobutyraldehyde. The N release of IBDU is
through hydrolysis. The rate of IBDU N release is accelerated by low pH and high
temperature. IBDU is also a good CRF candidate to apply for cool-season because its
release is not microbe dependent. Crotonylidene diurea is produced by an acid
catalyzed reaction of urea with either crotonaldehyde or acetaldehyde. The release of
CDU is through a combination of hydrolysis and microbial decomposition. The rate of
CDU N release is also accelerated by low pH and high temperature because CDU
degrades more rapidly in acid soils and with high microbial activity.
Previous research indicated that IBDU tended not to produce as favorable growth
response as other CRFs in warm-season or with excess rainfall. For instance, Elkashif
et al. (1983) reported lowest total tuber yields and 25% lower marketable yields with
IBDU treatment compared to either AN or IBDU/AN blends for potato production in
Florida. CDU is produced in Japan or Europe thus it has limit to use in the U.S.
35
Nutrient Release Formula of CRF
A nutrient release formula can be used to estimate nutrient release from CRF
under variable environmental conditions. Among CRFs, PCU and PSCU have shown
the most promising results for Florida potato production because of product longevity
and providing greater nutrient use efficiency. Manufacturers can adjust the rate of
release by altering composition of coating and the coating thickness to match with a
particular crop production model. The release formulas of PSCU or PCU are discussed
in this research.
The previous research has shown that the temporal patterns of PCU release are
generally sigmoid indicating that the release is complex and non “Fickinan” (nonlinear
process) (Shaviv et al., 2003). Based on the assumption that the released nutrients from
PCUs are controlled by simple solute diffusion, Jarrel and Boersma developed a
mathematical model for urea release from sulfur-coated urea (SCU) granules. The
diffusion of sulfur coating was defined as viscous transport in water, which is different
from the release through polymeric-membrane coating. Glaser et al. applied a one
dimensional coordinate system by introducing nonlinearity into release using a time
dependent parameter, the diffusion coefficient D. Time independence was based on an
experimental observed lag period w in the simulated release curve (Shaviv et al., 2003).
Further work by Lu and Lee (1992) separated the release process into two phases of
linear and decaying release but did not account for a lag period. The comprehensive
model developed by Shaviv et al. (2003) based on the vapor and nutrient diffusion
equations predicted the release stages in terms of measurable geometrical and
chemophysical parameters such as granule radius, coating thickness, saturation
concentration, and density. They further developed a statistically based model on the
36
basis of diffusion release from a single granule to address the large variation of within
populations of geometrical and chemophysical parameters in coated CRFs. The
diffusion based models by these previous workers attempted to describe the release
from a single CRF granule and are very helpful for manufacture to adjust their products
for an appropriate release period. However, most equations are complex in practice and
environmental and time factors were minimally taken into consideration.
Although water diffusion is required, speed of nutrient release from the prill is
primarily affected by soil temperature and not moisture (Gandeza et al., 1991). Maeda
(1990) evaluated various soil factors affecting N release and reported that temperature
accounted for about 83%, soil moisture accounted 11%, and other soil factors such as
microbial activity and pH and their interactions each accounted for less than 1% of the
release rate. Only when soil moisture was less than the plant wilting point (10 kPa),
does soil moisture become the primary controlling factor in nutrient release speed
(Fujita et al. 1983 and Fujita, 1989). Dry soil conditions limits diffusion of nutrients away
from the prill. The high correlation between nutrient release speed and change in soil
temperature allows for dependable prediction of nutrient release in temperature
controlled systems. Gambash et al. (1990) used a semiempirical approach to model the
nutrient release from a group of coated CRF. Assuming time and temperatures were the
main factors, they predicted N release in experiments with soil under different
temperature regimes with CRFs that had linear release patterns. A quadratic equation
to correlate cumulative N release (CNR) from a group of polyolefin-coated urea
granules associated with soil temperature, was defined as CNR=a+b(CT) +c(CT)2.
However, there is the poor explanation for the lag period of CRF release by this
37
equation. A simple release parameter may exist for a particular PCU with certain
geometrical and chemophysical parameters from release profile evaluation. A practical
formula can be developed with a combination of the parameter and release period for
an accurate estimate under varying temperature conditions.
Nitrogen Use Efficiency
The potato biomass production per unit of N supply varies among cultivars,
resulting in different N use efficiency (NUE). The different NUE among cultivars can be
explained by: N untaken efficiency and N utilization efficiency (Errebhi et al., 1998). The
increase of N uptake and utilization efficiency will increase productivity per unit of
nutrient while nutrient loss and environmental impacts decrease.
NUE may have different definitions depending on the goals of the research
program. For a particular cultivar, NUE can be defined as the ability to produce high
yield in a soil that is limited for that element for that cultivar (Graham, 1984). A further
definition developed by Blair (1993) indicated that NUE describes the ability of a
cultivar/genotype to acquire nutrients from a growing medium and/or to incorporate or
utilize them in the production of shoot and root biomass or utilizable plant material
(seed, grain, fruits, forage). The difference of NUE among species may be attributed to
morphological, physiological, and biochemical processes in plants and their interaction
with climatic, soil, fertilizer, biological and management practices (Baligar et al., 2001).
According to Baligar et al. (2001), NUE is affected by several factors including soil
characteristics, fertilizer type and quantities, plant uptake and use mechanisms,
agronomic practice, and cover crop usage, biological contributions, and climate. NUE
can be increased through the appropriate integration of all of above factors. Increasing
NUE is very important to improve crop yield and quality with the reduced fertilizer input.
38
Prihar et al. (2000) divided NUE into categories of agronomic NUE, economic
NUE, and nutrient recovery efficiency. According to his definitions, agronomic NUE is
expressed as the amount of yield increase obtained per unit of fertilizer applied when
compared to the yield of an unfertilized crop. Economic NUE refers to the returns on
investment in added nutrients, where the cost of the last unit of fertilizer applied equals
the value of the yield increase obtained by that addition fertilizer. The apparent nutrient
recovery is the amount of nutrient taken up by the crop and divided by the amount
applied as fertilizer, independent of the source from which the nutrient may have been
obtained. The nutrient recovery efficiency (NRE) is calculated to determine the amount
of nutrients available for movement from the site, (Zvomuya et al., 2003; Westermann et
al., 1988). Zvomuya defined the nutrient recovery efficiency (NRE) as the fraction of an
applied nutrient that is recovered or removed from the site. NUE discussed in this
dissertation is referred to as the percentage of recovery of an applied nutrient in plant
tissue.
Nutrient Loss under the Leaching Events
Nitrogen leaching typically represents the primary mechanism of N loss from
potato production systems in Florida. In a early study of N budget over a twelve-month
period for potato grown in a sandy soil in Denmark with fertilization by mineral fertilizer
and liquid hog manure, indicated that approximately 85% of N lost to the environment
was lost by nitrate leaching (Jensen et al., 1994). The IFAS recommendations stated
that rainfall of 7.5 cm in 3 days, or 10 cm in 7 days on coarse-textured soils lead to
nutrient leaching (Olson and Maynard, 2003). In a leaching event, growers can apply an
additional 34 kg N ha-1 under IFAS recommendations (Hutchinson et al., 2002a). The
nutrient loss not only affects potato tuber yields and quality, but also diminishes water
39
quality by allowing nutrients to accumulate into watersheds. Therefore, excess rainfalls
accelerate this phenomenon.
Zvomuya et al. (2003) reported that NO3-N leaching increased rapidly with
increased fertilizer N rate. The increase of nitrate leaching when N rate increased was
attributed to an excess of applied N that could not be taken up by plants (Gasser et al.,
2002). Nitrogen source, placement and application timing can also affect the risk of
nitrate leaching. Currently, split fertilizer application has been recommended by IFAS to
growers in order to reduce N leaching. Alternative fertilizer programs (CRF source,
application timing, placement, etc) are still under evaluation to develop the best program
to maximize yield while reducing the nitrate leaching.
Research Objectives
The release characteristics and field performance of a new CRF program needs to
be investigated before it can become commercially acceptable. The information would
help to direct the field cultural practice in order to maximize the nutrient use efficiency.
Therefore, nutrient loss under the leaching rainfall would help to adjust the current BMP
program in order to maximize yields with reducing pollution of water quality. In all, the
objectives of this work were to:
1. Determine nutrient release characteristics of various controlled-release fertilizers under controlled conditions.
2. Evaluate the influence of CRFs for potato production and tuber quality under northeast Florida production.
3. Compare the nutrient use efficiency of different fertilizer programs under northeast Florida production.
4. Evaluate the alternative variety yield and tuber quality for northeast Florida production
40
5. Estimate potential nutrient in-row movement under the leaching events in northeast Florida production.
41
CHAPTER 3 SIMULATION OF NITROGEN RELEASE FROM POLYMER-COATED FERTILIZERS
IN A CONTROLLED SYSTEM
Introduction
Controlled release fertilizers (CRFs) are formulated to release nutrients over time
and at a quantity which synchronizes with plant nutrient uptake and growth (Pack et al.,
2006). Therefore, they may increase nutrient use efficiency, minimize nutrient losses,
and protect environmental quality. One disadvantage of CRFs is the difficulty to quantify
and predict nutrient release, especially for new CRF products. A complete laboratory
evaluation of CRFs and a release formula to predict nutrient release under field
conditions would help to identify the appropriate CRFs for a particular production
system and develop fertilizer programs prior to expensive field experiments.
Polymer coated urea (PCU) and polymer sulfur-coated urea (PSCU) are two CRF
products with different formulations and nutrient release mechanisms. PCU is coated
with a polymer coating film, which is typically composed of a blend of water permeable
and impermeable resins and surfactants (polyolefin or polyethylene), ethylene, vinyl
acetate, and talc occurring as layered plates (Shoji, 1999). PSCU utilizes a primary
coating of sulfur and a secondary polymer coat such as polyolefin and polyurethane.
Most PCU products release N by water diffusion through a semipermeable membrane.
Manufacturers can change the release rate of PCU by altering the composition of the
coating and coat thickness. Alternatively, the N release mechanism of PSCUs is a
combination of water diffusion and capillary action.
Although water diffusion is required, N release of PCU is primarily affected by soil
temperature but not soil moisture (Gandeza et al., 1991). N release properties of PSCU
fertilizers are also temperature dependent, however, they are less temperature sensitive
42
than most polymer-coated fertilizers because of the combination of coatings. Maeda
(1990) evaluated various soil factors affecting N release of one particular PCU product
and reported that temperature accounted for about 83%, moisture content accounted for
11%, and other soil factors (microbial activity, pH and their interactions) accounted for
less than 1% of the N release rate. Only when soil moisture is less than the plant wilting
point (10 kPa), does soil moisture become the primary controlling factor in N release
because dry soil limits diffusion of nutrients away from the prill (Fujita et al., 1983; Fujita,
1989). Pack (2004) developed a stable laboratory water incubation method to evaluate
the N release profile of PCUs.
Using the logarithm of the concentration of intact fertilizer in the soil, Kochba et al.
(1990) developed rate constants of coated urea release at different temperatures that
are linearly related to the vapor pressure as:
K=APw+B (1)
where Pw is the vapor pressure and A and B are constants. This formula provides an
estimate of N release under varying temperature conditions by indirectly measuring their
release rate K and release constant A and B. However, since the vapor pressure (Pw) is
directly related to temperature (Kochba et al., 1990), the formula may need to also
describe the linear relationship between release rate (K) and temperature (T) as
K=AT+B. Kochba et al. also described the relationship between the N release and
release rate as the logarithm formula:
ln[(Q0-Qt)/Q0]=-Kt (2)
where Qt represents nutrient quantity released up to time t (Qt), Q0 represents the
amount of N at the beginning of release and t represents the release time. Therefore, if
43
considering the N release of PCUs under varying temperature as the sequence of N
release at constant temperature at certain time, the formula (ii) can be further developed
to estimate N release under varying temperature, simulating the actual N release under
field conditions.
The objectives of this research were to 1) evaluate the N release profile of CRFs in
a controlled system; 2) evaluate a new linear formula of N release rate (K) associated
with temperature (T) for PCU products whose N release is strongly related to
temperature; and 3) quantify N release of PCUs under varying temperature and to verify
the accuracy of prediction model.
Materials and Methods
Experimental Procedure
Six incubators (MIR-153, Sanyo Electric Biomedical Co., Ltd, Osaka, Japan) were
set at constant temperatures of 5, 10, 15, 20, 25, and 30 ºC. Also, temperature in one
incubator was varied to match the 25 year weekly average soil temperature (10 cm
depth) starting on 25 Jan in Hastings, FL. Temperature in this incubator was adjusted
on the following schedule: week 1 and 2 (15 ºC), week 3, (16 ºC), week 4 and 5 (18
ºC), week 6 and 7 (19 ºC), week 8 and 9 (21 ºC), week 10 and 11 (22 ºC), week 12 (23
ºC), week 13 (24 ºC).
Six PCU products (CRF1 through CRF6) were evaluated for N release (Table 3-1).
CRF1, 2, 3, 4 were PCUs or tri-blended PCUs provided by Purcell Technologies, Inc.
(Sylacauga, AL) and were named as P-PSCU, P-PCU1, P-PCU2, P-PCU3(Tri),
respectively in this study. CRF5 and 6, provided by Haifa Chemicals Ltd. (Israel), were
PCUs and named as H-PCU1 and H-PCU2 in this study. Nitrogen (3 g N for each
product) and 100 ml of deionized (DI) water was placed in 200 ml sterile glass bottles
44
with screw caps. At weekly intervals, the bottles were shaken gently and a 20 ml aliquot
was removed and analyzed for N. Fertilizer prills were screened from the remaining
solution and returned to the appropriate bottle. Excess solution was discarded. Bottles
were refilled with DI water (100 ml). After 13 weeks from the beginning of experiment,
filtered prills were ground with a mortar and pestle and residual fertilizer was dissolved
in 100ml DI water and a 20 ml aliquot was removed (Pack, 2004).
Aqueous samples were stored at -5 ºC, until analyzed at the University of Florida’s
Analytical Research Laboratory (ARL) for total Kjeldahl N (TKN) using a standard
protocol (Mylavarapu and Kennelley, 2002). Weekly N release (WNR), and cumulative
N release (CNR), were calculated based on results of analysis and expressed as the
percentage of total available N (TAN) at the beginning of the experiment. A Q10 value
was defined as the rate of N concentration increase as temperature increased by 10 ºC.
Statistical Design and Analysis
The experiment was arranged in completely randomized design with three
replications. A regression analysis with groups (one for each fertilizer) was conducted
for all data using several response variables. A single non-liner fitting model was
conducted first for each of the incubator over its 13 measurements. The best fitting
model with the smallest overall sum of the squares was selected to apply on all series
corresponded to Gompertz from several biological growth models evaluation such as
Gompertz, logistic, general logistic, Chapman-Richards(Piegorch and Bailer, 2005). The
general expression of the model was:
Y=a exp [-exp (b-cx)] (3)
where y is defined as the response variable as cumulative release, and x is the
day of measurement (sampling). The cumulative N release at 91 days is defined as the
45
CNR91 as the most significant variable to evaluate for each CRF. The estimated a, b
and c are the parameters associated with the cumulative nutrient release of a particular
fertilizer. Specifically, the parameter a is a corresponding parameter as an asymptote, b
is a displacement parameter which in this experiment is a certain value 30000ppm
equal to original total available N concentration (3 g N in 100 ml DI water) and
parameter c is related to the rate of growth.
With the fitting model, the parameters (CNR 91, b and c) of each fertilizer were
analyzed using PROC MIXED as implemented in SAS based in the following model
Y=µ + fertilizer +temp +fertilizer × temp +fertilizer × temp2 + incubator + ε (4)
where fertilizer is a factor representing the fixed effect of fertilizer, Temp is a fixed
variable representing temperature, fertilizer x temp is the interaction among those two
elements, and incubator is a random effect of incubator. In addition, using the fitted
models, two summary variables were calculated for (1) days to reach 25% of the total
available nitrogen (TAN) of CRF (2) days to reach 50% of the total available N (TAN) of
CRF.
Development of Linear Formula for Release Rate (K)
The CRFs with temperature based N release were selected and their release rates
(K) were calculated by associating with each constant temperature (5, 10, 15, 20, 25, 30
ºC) using the formula:
ln[(Qt-Q0)/Q0]=-Kt (5)
For each PCU with temperature-based N release, the release rates associated
with constant temperatures were calculated. A linear regression analysis between
release rate and temperature was conducted to develop a linear formula describing the
relationship between release rate and temperature. Assuming that CNR of PCUs under
46
varying temperature was the result of N release at each constant temperature over time,
a model was developed to calculate CNR of each PCU under varying temperatures.
Model verification was conducted based on the experimental results of N release
of CRFs under the variable temperature set. CNR data under variable temperature in
the evaluation experiments were used to compare calculated and experimentally
measured release. Further, correlation analysis was used to determine accuracy of the
model.
Results and Discussion
CNR91
CNR91 was defined as the cumulative N release at 91 days and was expressed
as percentage of total available N (TAN) at the beginning of the experiment. The
analysis of CNR91 indicated that at the low temperature, CNR91 of CRFs had a
significantly greater difference among CRFs than at the high temperature (Figure 3-1).
Therefore N release of polymer coated fertilizers was mainly affected by soil
temperature, the primary factor controlling CNR (Fujita et al., 1983 and Fujita, 1989;
Gandeza et al., 1991). Florida potatoes or other spring crops are grown as temperature
changes from cool to warm (Hutchinson et al., 2009). Generally, potato plants have a
relatively low N requirement at early life cycle and increase slightly of the N requirement
during tuber initiation stage, with the highest N requirement occurring at the tuber
bulking stage (Ojala et al., 1990). The release primarily affected by temperature offer a
better likelihood to synchronize potato plant N during growing season.
The CNR91 of P-PSCU and H-PCU2 were greater than other CRFs evaluated
under the same temperature, indicating a faster N release rate. The fast N release of P-
PSCU and H-PCUs may be attributed to their relatively thin coating. The thickness of
47
coating membrane was reported as the most important parameter in controlling N
release superior to granule radius of fertilizer prill (Du et al., 2008). The fast N release
rate is more favorable for Florida short season in terms of avoiding nutritional stress
under frequent leaching rainfall and irrigation (Worthington et al., 2007). At 5 ºC, P-
PSCU and H-PCU2 released 100% and 68.3%, respectively, of total available N (TAN),
indicating N release was less temperature sensitive. The N release under low
temperature may facilitate fertilizer application during winter plantings in North Florida.
The sufficient N early in plant growth development is important for Florida short growing
season for optimum yields (Goins et al., 2004).
The CNR91 of P-PSCU decreased when temperature increased from 5 to 20 ºC
then increased when temperature increased from 20 to 30 ºC. This release character
may be attributed to the PSCU dual release mechanism, a combination of diffusion and
capillary action. For the release of PSCU, water vapor first diffuses through the
continuous polymeric membrane layer, then subsequently penetrates the defects in the
sulfur coat through capillary action and solubilizes the fertilizer core. However, the N
release of PSCU has been minimally investigated. The possible reason only can be
presumed that when temperature increased from 5 to 20 ºC, there may be minimally
increase in the speed of water diffusion while capillary action was reduced.
Nitrogen release from P-PCU2, H-PCU1 and H-PCU2 was a gradual non-linear
increase curve of CNR91 with increasing temperature from 5 to 30 ºC as compared to a
linear increase curve of CNR91 from P-PCU3(Tri) and P-PCU1. The difference was
attributed to the different coating material or thickness (Trenkel, 1997; Du et al., 2008).
For P-PCU2, H-PCU1 and H-PCU2, the coating material or thickness was not resistant
48
to high temperature. The ratio of increase in release rate was reduced following a
temperature increased from 5 to 30 ºC with a slow increase when temperature was
above 20 ºC. In contrast, the CNR91 of P-PCU1 and P-PCU3(Tri) linearly increased as
temperature increased from 5 to 30 ºC as their coating materials were thicker or more
resistant to high temperature. These two CRFs may be more suitable for a long growing
season or with a portion of N applied prior to planting such as at time of fumigation
(approximately 3 weeks prior to planting), as they have long nutrient release periods. If
a short release period is desired, the manufacture may also want to consider adjusting
the coating thickness of those PCUs.
Asymptote (a) from Gompertz Model
In this study, the asymptotes (a) from the Gompertz model represented the ability
for CRFs under each temperature to reach the upper limit (% TAN) when release period
is approaching infinity. The asymptote (a) of CRFs had a similar trend as the CNR91s
with the greater difference between CRFs at a low temperature (Figure 3-2). The
asymptotes of PSCU decreased from 5 to 20 ºC and increased when temperature
increase from 20 to 30 ºC while asymptotes of PCUs increased following temperature
increase. Similar to CNR91, PSCU can be used for cool season crops due to less
temperature sensitivity for release. Nitrogen release of PCUs was extremely slow under
low temperature, indicating PCUs are not optimal fertilizers for cool season crop
production even when the release period is extended (long growing season). The
asymptotes of H-PCU1 did not reach 80% TAN even under high temperatures due to
“lock-off” effects. These “lock-off’ effects were typically reported for CRFs with thicker
coating, resulting in a very slow release rate after a majority of N was released (Shaviv,
1996). PCUs with “lock-off’ may not provide sufficient N for plant demand and create a
49
concern for environmental quality due to high residual N left in the soil after the growing
season. This high residual N was also reported by Park (2004) in CRF evaluations with
up to 65.8% TAN for some products with temperatures under 30 ºC. The linear curves
of asymptotes from P-PCU1 and P-PCU3(Tri) indicated that a portion of nutrient inside
these two fertilizers may be released under temperatures above 30 ºC.
Growth Rate Parameter(c) from Gompertz Model
Since the growth rates of CRFs were small numbers, all the growth rates were
evaluated at 10,000 times their value. The growth rate parameters(c) of CRFs gradually
increased as temperature increased from 5 to 30 ºC except that P-PCU3(Tri) slightly
decreased from 5 to 12.5 ºC then increased when temperature increased from 12.5 to
30ºC (Figure 3-3). Similar as CNR91 and asymptote (a), there were greater differences
among CRFs when temperature increased, indicating the N release of CRFs was
accelerated when temperature increased. The higher growth rate of the P-PSCU and H-
PCU2 indicated that N releases of these two CRFs were accelerated greater when
temperature increased. The temperature and coated membrane thickness were
considered as two important factors that determined diffusion coefficients (Du et al.,
2006). The smaller increase of growth rate for other CRFs may be attributed to thicker
coating, resulting in less increase in the speed of water diffusion when temperature
increased.
Days to Reach 25% TAN and 50% TAN
The time curves to reach 25% TAN for P-PSCU and H-PCU2 decreased linearly
as temperature increased (Figure 3-4). The curves of other CRFs with slower release
rates than P-PSCU, H-PCU2 decreased non-linearly when temperature increased.
Under high temperature (30 ºC), P-PSCU and H-PCU2 released 25% N after 1.9 days
50
while under the low temperature (5 ºC) it required 14.1 and 19.4 days, respectively, to
release 25% TAN. The P-PCU1 had very slow release rate resulting in the longer days
to reach 25% TAN under the low temperature.
The time curves to reach 50% TAN for fast release P-PSCU and H-PCU2
decreased linearly as temperature increased (Figure 3-5). The curves of other CRFs
with slower release rates than P-PSCU and H-PCU2 decreased non-linearly as
temperature increased. Time required to release 50% of TAN from P-PCU1, P-PCU2,
P-PCU3(Tri) and H-PCU1 were longer than 50 days at a constant temperature of 15°C
or lower. The average soil temperature during the first 3 weeks after planting was
roughly 15°C in the TCAA of northeast Florida (FAWN, 2009). Therefore, these CRFs
with relatively slow release may not be appropriate fertilizer candidates for cool season
grown crops such as potatoes as they are grown in north Florida during winter and
spring.
Evaluation of Fertilizer Candidates
The evaluation of appropriate CRF fertilizer candidates was based on a release
profile of CRFs under the variable temperatures that simulated to field conditions. The
CNR curves of P-PSCU and H-PCU2 had a sigmoidal pattern without a lag phase and
reached a decay stage around 60 days and 90 days, indicating a 60 and 90 day release
with 100% and 90% TAN, respectively. The low nutrient level from H-PCU2 at the decay
phase may not create a strong enough driving force to release all N from its coating,
resulting in ‘lock-off’ effect (Shaviv, 1996; Shaviv, 2005). CNR curves of P-PCU1, 2
3(Tri) and H-PCU1 had a relatively linear release rate following time of 53%, 78%, 66%,
and 75%, respectively. Nutrient release from CRFs with linear and simoidal patterns can
synchronize plant demand better than the parabolic (Fickian) pattern (Shaviv, 1996).
51
The nutrient release of a polymer-coated fertilizer generally has 3 distinct stages: initial
minimal release (lag period), a constant-release stage, and a stage of gradual decay of
release rate (Shaviv, 1996; Du et al., 2006). At the initial lag stage, water vapor
penetrates inside of the fertilizer prill to dissolve soluble nutrients and to develop
pressure (Kochba et al., 1990; Shaviv, 2003). The lag stage was only observed for P-
PCU1 followed by a linear increase release while other CRFs examined already passed
the lag stage at first sampling date (7 days of incubating). The length of the lag stage
may vary depending on the coating materials and thickness. The sigmoidal release
without lag phase generally occured for PCUs with polyolefin coating (Shaviv., 2005).
The lag phase would help to prevent the early nutrient losses but may attributed to
insufficient N supply under a fast development in crop early life cycle.
The CNR of P-PSCU had a high initial release with 25%, 48% and 62% and 75%
TAN after 7, 14, 21, and 28 days, respectively. The tailing effect was not found for the
P-PSCU in this study with 100% TAN release within 60 days. Shaviv (1996) reported
the “burst’ effect for a PSCU with high initial N release 22% TAN at first day in free
water and a tailing phase (18% TAN lock-off) as compared with several PCUs. This
PSCU was also reported with high potential nutrient leaching in the early season and at
low nutrient use efficiency. The “lock-off” was reported to sulfur coating because of very
thick coating (Shaviv, 1996). PSCUs are a product coated primarily with sulfur to reduce
the cost of the outside polymer. The sulfur coated products generally can be divided in
damaged coating crack, damaged coating sealed with wax, and perfect and thick
coating (Shaviv., 2005). The high initial N release of PSCU may be attributed to a
relatively thin layer of polymer providing minimal protection for the inside imperfect
52
sulfur as compared with most PCUs, resulting in less resistance to water penetration.
Therefore, P-PSCU may be an adequate fertilizer candidate for Florida’s short season
potato crop to reduce split applications of soluble fertilizers and potentially leaching in
the early season if heavy rains occur.
Other CRFs examined in this study did not have the delay stage within 91 days
because of slow release rates. P-PCU3 (Tri) released 53% and 66% TAN, respectively,
at 91 days (Figure 3-6), resulting in high residual nutrient N potentially remaining after
harvest. Therefore, P-PCU1 and P-CU3(Tri) would not be considered as appropriate
fertilizer candidates for Florida potato production due to insufficient N release during the
short growing season. P-PCU2 and H-PCU1 released 78% and 75%, respectively, TAN
by 91 days with low initial N release during the early season (less than 50% after 50
days). The CNR of P-PCU2 and H-PCU1 may not provide sufficient N at early season
under field condition, which would lead to a reduction in tuber yields and quality. These
two CRF fertilizers would have to be blended with soluble N fertilizer in order to provide
sufficient N during the early season. The CNR curves of P-PSCU and H-PCU2 had a
fast N release under simulated field soil temperature, releasing 100% and 90%,
respectively TAN at 91 days. P-PSCU and H-PCU2 released 50% of TAN between 14
to 21 days and 21 to 28 days, respectively. The optimal N application timing was
suggested by UF/IFAS to split half to two-thirds of the fertilizer applied at planting with
the remainder applied between 30 to 40 days after planting for Florida potato production
(Hochmuth and Cordaso, 2000). Therefore, one -time application of P-PSCU or H-
PCU2 at planting may supply the N demand for potatoes simply to that of a soluble N
fertilizer slit application. The non-linear curves for CRN of these two CRFs indicated a
53
slower increase in release rate at late season when temperature increased later in the
season, providing 97% and 80%, respectively, TAN release at 56 days. The CNR curve
of P-PSCU became static after 60 days indicating that P-PSCU was a ‘60 day release’
CRF while the H-PCU2 was a ‘90 day release’ CRF with almost no N release occurring
after 90 days. Therefore, P-PSCU and H-PCU2 may be appropriate fertilizer candidates
for Florida potato production and should be considered for future field evaluation.
Q10 Value
All CRF x temperature treatments had the same amount of available N at the first
sample date. Therefore, CNR at the first sampling date, at each temperature provided a
relative accurate estimate of Q10 values for each CRF (Table 3-2). Q10 values after the
first sampling date were not calculated in this study because of the different amounts of
remaining N after the first sampling date (Pack, 2004). During a normal potato growth
season in Florida, Q10 values for biological activity can be calculated from 15 to 25 ºC or
20 to 30°C. Between these two temperature ranges, fertilizer manufacturers would
expect available N uptake potential to increase by a factor of 2 (the factor of increase in
biological activity). Du et al. (2006) reported a Q10 value between 1.8 to 2.0 for the free
water and the water saturated sand, respectively when temperature increased from 20
to 30°C. However, only two PCU products from the same manufactures were selected
in the study, so it did not represent the diversity of current CRF products. From our
findings, Q10 values varied considerably over the temperature range and over CRF
products. Therefore, understanding the dynamics between soil temperature change
over the season, available N released from CRF, and crop demand at different growth
stages are important factors in determining the proper CRF for each production system.
54
Linear Formula for Release Rate
The N release profile indicated that P-PSCU and H-PCU2 were less temperature
dependent for N release, and released N relatively rapidly. In this study, the CRFs with
high temperature dependence for N release were chosen (P-PCU1, 2, 3(Tri), and H-
PCU1) to determine their linear formula of release rate. The linear formula of release
rate assumed that CNR is affected by the amount of N available, release parameter
associated with a certain constant temperature and release period.
The release patterns for P-PCU1, 2, 3(Tri), and H-PCU1 were calculated using the
formula under each constant temperature. In this formula, the K value is defined as the
slope of the linear relationship between the natural logarithm of percent of remaining
available nitrogen [(Q0-Qt)/Q0] and release time (t). Therefore, for each slow release
PCU, the estimated K value associated with each constant temperature was calculated
by the simple linear regression model:
(6)
In this formula, xi is defined as release time t. Yi is defined as the logarithm of
percent of remaining available N at time t. For each PCU, calculated release rates (K)
associated with constant temperatures were plotted and solved for their linear
relationship with temperature (Figure 3-7). In each linear formula of K, A is the slope of
the linear relationship for a particular PCU between the K value and temperature, B is
the intercept. The linear formula of K over temperature for P-PCU1, 2, 3(Tri), and H-
PCU1 had A values of 0.0006, 0.0008, 0.0005 and 0.0008, respectively (Table 3-3). The
higher A values for P-PCU2 and H-PCU1 indicated that N release from these two PCUs
increased rapidly when temperature increased when compared to P-PCU1 and P-
55
PCU3(Tri). The linear release rate of P-PCU2 had a higher B value indicating that P-
PCU2 would have a higher N release compared with H-PCU1 if they had the same
available N for release under the same temperature.
The nutrient release of PCUs by water diffusion was described as a process decay
of a fertilizer-particle population, which follows first-order kinetics (Berry et al., 1980;
Kocha et al., 1990). The first-order kinetics used to describe the nutrient release by
coated fertilizers was formulated as the equation (2). This equation can also explain the
“lock-off” effect of N release from PCUs observed in this study because at the late stage
when the majority of N was released, t (time) would be a large number in order to
release very small portions of available N inside fertilizer prill, resulting in a typical
“decay” stage. If the polymer membrane slowly fails under certain field conditions, the
entire nutrient load in the granular prill may release instantaneously (Goertz, 1995).
However, the “failure mechanism’ was only typical of fragile, non-elastic coatings, such
as sulphur or other inorganic coatings (Shaviv, 2005). Therefore, the residual N of
PCUs due to a “tailing” effect may generate a concern for environmental quality and
nutrient use efficiency if inappropriate coatings are chosen.
By using first-order kinetics, Kochba et al., (1990) reported release rates at
different temperature were linearly related to water vapor pressure, which varied by
temperature. The release rate (K) directly reported the percentage of TAN release in a
day under any given temperature. The study in this dissertation further reported the
release rates were linearly related to temperature. The linear formula developed in this
study allowed characterizing release rate for any given PCUs with release by water
diffusion. For example, to formulate a PCU for Florida potato production with 90% N
56
release within a growing season (100 days), the release rate averaged seasonal
temperatures higher than 0.0230 (-ln0.1/100=0.0230 %TAN day) may be recommended
to manufacturers. Similar as the previous evaluation, release rate (K) of P-PCU1, P-
PCU2, P-PCU3(Tri) and H-PCU1 did not exceed 0.0200 under simulated Florida
seasonal temperature (Table 3-4), resulting in insufficient release during the growing
season. The new linear formula in this study can be used to simulate or predict release
rate at any given temperature, which makes further prediction under variable
temperature feasible.
Mathematical Model under Variable Temperature
Soil temperatures vary over the entire growing season. Therefore a mathematical
model under variable temperature would be more valuable to estimate N release from
PCU in a production system. From the formula (ii), the relationship between Qt, release
rate and time at any given temperature can be expressed alternatively as
Qt=Q0[1-exp(-KΔt)] (7)
The formula of CNR under varying temperature assumes that N release under
varying temperature can be considered as the sequence of release under changing
temperatures over time. During a period of constant temperature, the formula (ii) can be
used to calculate CNR. With the decrease of the amount of available N after the initial
release, the amount of available N for release when a temperature change occurs is
equal to the available N at the prior temperature minus the amount of N released during
the period of prior temperature. CNR release under a variable temperature would be
considered as the sum of Y at different temperatures over the experimental period time:
Ytn=Sum(Qt1+Qt2…..+Qtn) (8)
57
Where Y is defined as the CNR under a variable temperature at time t; Qt1 is
defined as the amount of release N during the first release time t1. Qtn is defined as the
amount of release N during the release time tn.
There are several existed nutrient prediction models to simulate N release from
PCUs. For example, based on the assumption that the release nutrients from PCUs are
controlled by simple solute diffusion, Jarrel and Boersma (1980) developed a
mathematical model for urea release from sulfur-coated urea (SCU) granules. The
diffusion of sulfur coating was defined as viscous transport in water, which is different
from the release through polymeric-membrane coating. Several models were made in
an attempt to apply diffusion based mechanistic approach simulating nutrient release
from fertilizer prills (Glaser et al., 1987; Lu and Lee, 1992). However, these models
were complex and did not account for the major release driving force temperature. A
semiemperical approach for modeling nutrient release was developed by Kochba et al.,
(1990) which considered the nutrient release as a first-order decay process. However,
this model predicted nutrient release related to vapor pressure which also varies by
temperature. Also, the feasibility of prediction was not tested under actual varying
temperature. Our findings tested the prediction model directly with temperature under
varying temperatures, simulating actual field conditions. There were other prediction
models in terms of measurable geometrical and chemophysical parameters such as
granule radius, coating thickness, saturation concentration and density (Shaviv et al.,
2003; Du et al., 2008). Beside the complexity of most equations, the model did not
consider the environmental factors which made it of less practical use.
58
Model Verification
Verification of the model was based on experimental results of release data under
the variable temperature set. Since the estimated release under variable temperature is
more important and similar to the actual release conditions under field conditions, N
release under variable temperatures were used to verify the prediction model (variable
temperature set is the simulating temperature set based on a 25 year weekly average
10 cm depth soil temperatures starting on 25 Jan in Hastings, FL). Experimentally
measured release curves were close to the corresponding release curves which were
obtained by calculation according to the estimation formula (Figure 3-8). During the
early releasing period, the actual cumulative releases were slightly lower than the
calculated cumulative release for P-PCU1, P-PCU2 and H-PCU1 because at early
release stages the time needed for water to diffuse into prills and to dissolve the nutrient
in question led to a high nutrient gradient inside the prill just before release. Calculated
results at late release were very similar to the actual release after 40 days. The actual
cumulative release was relatively higher than the calculated cumulative release for P-
PCU3(Tri), a blended CRF which included a certain percentage of very fast release
PCU. The PCU with fast relate in P-PCU3(Tri) may have had very thin coating and was
less temperature sensitive resulting in higher actual release than the calculated release
. The correlating (r2) value for all four PCUs were higher than 99% indicating the release
model could be successfully applied to predict the nutrient release under the variable
temperature.
Overall, the protocol used in this study provided an effective tool to evaluate
nutrient release from polymer coated CRF. The evaluation also reinforced the
temperature was the major driving force for N release from polymer coated fertilizers.
59
Under the evaluation in this study, P-PSCU and H-PCUs were determined as the
potential candidates for Florida potato production for further evaluation. However, the
high initial nutrient release of P-PSCU may be a concern for nutrient losses in early
season. The “lock-off’ effect of PCUs may be a concern for H-PCUs with nutrient
residual left after the crop season.
The release key responses studied (CNR91, a and c) increased as temperature
increased indicating a fast release under higher temperature. The formula of release
rate (K) associated with temperature successfully described the nutrient release by
water diffusion from PCU under varying temperatures. The linear release formula
allowed simulating release rate under any given temperature and accurately predicting
nutrient under varying field conditions. The release rate (K) needs to be above 0.023 for
Florida potato production to ensure 90% of N release within season. The prediction
model provided an effective tool to simulate N release in accordance with the agronomic
and environmental factors. The formulation of the model considers only one release
parameter instead of many complex geometric and chemophysical parameters resulting
in a more realistic way of modeling nutrient release. An effective fertilizer program can
be developed for a particular type of crop production in order to maximize the nutrient
use efficiency and minimize the loss. Further field application would be helpful to
consider other environmental factors such as moisture, microbial activity, pH for
modifications of the model.
In all, the laboratory evaluation in this study successfully provided N release
profiles of CRFs and determined appropriate fertilizer candidates for a particular
production before an expensive field study.
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Table 3-1. Fertilizer treatments, manufactures, and rates in the fertilizer program evaluation in Hastings, FL, in 2006.
Type Fertilizer type Name Manufacturer Formulationz 1 PSCU P-PSCU Purcell Technologies, INC 42-0-0 2 PCU P-PCU1 Purcell Technologies, INC 43-0-0 3 PCU P-PCU2 Purcell Technologies, INC 44-0-0 4 Tri-Blended PCU P-PCU3(Tri) Purcell Technologies, INC 42.7-0-0 5 PCU H-PCU1 Haifa Chemicals 40-0-0 6 PCU H-PCU2 Haifa Chemicals 42-0-0
zN-P2O5-K2O
Figure 3-1. The cumulative nitrogen release (CNR) expressed as percentage of total
available N (TAN) at the day 91 associated with temperature for each CRF under the temperature controlled system.
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Figure 3-2. The asymptote for a Gompertz model (a) of each fertilizer associated with temperature.
Figure 3-3. The growth rate from a Gompertz model (c) for each CRF associated with the temperature.
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Figure 3-4. The estimate days for 25% release of total available nitrogen (LD 25) for
each CRF associated with temperature.
Figure 3-5. The estimate days to reach 50% release of total available nitrogen (LD 50)
for each CRF associated with temperature.
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Table 3-2. Q10 values for various PCUs at 7 days sampling time. Biological range (⁰C) P-PSCU P-PCU1 P-PCU2 P-PCU3(Tri) H-PCU1 H-PCU2 5-15 1.21 1.18 1.16 1.16 1.8 2.23 10-20 1 1.12 1.79 1.23 1.86 1.75 15-25 1.54 1.66 1.65 1.27 3.18 1.3 20-30 2.54 3.81 1.44 0.98 3.51 2.55
Figure 3-6. CNR release curve of each CRF at variable temperature setting over the
duration of the incubator experiment. TAN = total available nitrogen.
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A B
C D
Figure 3-7. The linear relationship of release parameter of PCUs and temperature of the incubator experiment. A) P-PCU1. B) P-PCU2. C) P-PCU3(Tri). D) H-PCU1.
65
Table 3-3. Nitrogen release rate K associated with constant temperature for different PCU productsz. Temperature (ºC)
Fertilizer 5 10 15 20 25 30 R2 value P-PCU1 0.0023 0.0033 0.0051 0.0918 0.0131 0.0183 0.9447 P-PCU2 0.0060 0.0081 0.0135 0.0186 0.0228 0.0243 0.9774 P-PCU3(Tri) 0.0056 0.0073 0.0085 0.0124 0.0167 0.0183 0.9631 H-PCU1 0.0054 0.0083 0.0113 0.0167 0.0209 0.0236 0.9888
z N release rate K (-ln % TAN/day). Table 3-4. Nitrogen release rate K associated with variable temperature for different PCU productsz.
Temperature (ºC) Fertilizer 15 16 18 19 21 22 23 24 Linear Formula P-PCU1 0.0062 0.0068 0.0080 0.0086 0.0098 0.0104 0.0110 0.0116 K=0.0006T-0.0028 P-PCU2 0.0134 0.0142 0.0158 0.0166 0.0182 0.0190 0.0198 0.0206 K=0.0008T+0.0014P-PCU3(Tri) 0.0095 0.0100 0.0110 0.0115 0.0125 0.0130 0.0135 0.0140 K=0.0005T+0.0020H-PCU1 0.0129 0.0137 0.0153 0.0161 0.0177 0.0185 0.0193 0.0201 K=0.0008T+0.0009
z N release rate K (-ln % TAN/day).
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r2=0.994 r2=0.998
r2=1.0 r2=1.0 Figure 3-8. Comparion of PCU the actual release and calucated release of PCU under variable temperature over the
duration of the incubator experiment. A) P-PCU1. B) P-PCU2. C) P-PCU3(Tri). D) H-PCU1.
A
C
B
D
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CHAPTER 4 APPLICATION OF CONTROLLED-RELEASE FERTILIZER FOR NORTHEAST
FLORIDA CHIP POTATO PRODUCTION
Introduction
Nitrogen leaching or run off is a major concern of environmental water quality.
“Best Management Practices” (BMPs) have been developed and implemented in Florida
by state agencies aimed to reduce the load of nutrients entering water bodies while
maintaining crop productivity for growers. A major objective to implement BMP in the
Tri-County Agricultural Area is to reduce NO3-N movement from agricultural land to the
St. Johns River basin. Seepage-irrigated potato (2n = 48; Solanum tuberosum L.) is an
important spring crop in TCAA with 7300 ha of production. Production is vulnerable to
NO3-N leaching due to the shallow potato root system and potential for high rainfall
during the growing season. Current BMP is for potato production on seepage irrigation
facilitates N at 224 kg ha-1, with the possibility to side-dress up to 34 kg ha-1 after
leaching rains of 7 cm in 3 days or 10 cm in 4 days.
CRFs are formulated to slowly release nutrients to plants over time. The slow
release offers the potential to delay N availability thereby avoiding leaching during major
rain events. CRFs may improve potato production and quality by synchronizing growth
with nutrient demand of the plant. Therefore, with slow N release and higher use
efficiency, CRFs may facilitate growers to maintain or improve tuber yields while
reducing the potential risk of N leaching, particularly under heavy rainfall.
CRFs have been successfully used for potato production. ‘Russet Burbank’
potatoes grown on a sandy soil in Minnesota produced greater marketable yields using
polymer coated urea applied at planting as compared with urea applied at emergence
and hilling at application rates ranging from 110 to 290 kg N ha-1 (Zvomuya and Rosen,
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2001). Pack et al. (2006) reported that CRF-treated plants produced greater or similar
tuber total and marketable yields as compared to plants fertilized with ammonium nitrate
(AN) resulting in lower N concentrations at the root zone during the early season.
Zvomuya et al. (2003) reported that at 280 kg N ha-1, NO3-N leaching was 34 to 49%
lower with PCU treatments than three split applications of urea while N recovery
efficiency (NRE) for PCU averaged 50%, 7% higher than urea (43%).
There are currently several CRF products marketed for vegetable production with
different release mechanisms and recommended application rates. Potato plants have a
relatively low N requirement during their early life cycle and this N requirement
increases slightly during tuber initiation stage, with the highest N requirement occurring
at the tuber bulking stage (Ojala et al., 1990). Soil temperatures in the TCAA are
relatively low at planting and then increase during late growth season. CRF products
with N release dependent on soil temperature may be manufactured to synchronize with
an N uptake profile for potatoes. However, a sufficient and continuous supply of N
during the early growth stages is important for emergence and early vegetative growth
(Goins et al., 2004). The lack of N at this stage may not be overcome by a late N
application, thereby reducing tuber yields. A successful CRF program may have the
CRF combined with a soluble or fast release fertilizer in order to have N delivered
throughout the growing season. Environmental factors such as soil temperature and soil
moisture vary during the growing season within and over production regions. Sources
and rates of CRF’s for potato production in the TCAA needs to be evaluated in order to
determine if they can be recommended for potato growers.
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The objectives of this research were to: a) evaluate the influence of CRF source
(FS) and fertilizer rate (FR) on potato tuber production and quality; b) evaluate N
availability at the root zone level and perched ground water under alternative fertilizer
program and; c) determine N recovery efficiency at different growth stage associated
with alternative fertilizer programs.
Materials and Methods
Site Description
The research plots were planted at the University of Florida’s Research Farm in
Hastings, FL in 2006. The soil was an Ellzey fine sand classified as sandy siliceous,
hyperthermic Arenic Qchraqualf with 90 to 95% sand, <2.5% clay, and <5% silt (USDA,
1983). Though the saturated hydraulic conductivity in the top 1 m is about 10 cm h-1,
the soil profile is poorly drained due to a compacted loamy find sand restricting layer 1
to 1.6 m below the soil surface (USDA, 1983). Potato plants were irrigated with
seepage irrigation which maintained water at an average depth 45-60 cm below the
surface of the row during the season to ensure appropriate moisture during the growing
season. Weather data was collected and recorded through the Florida Agricultural
Weather Network (FAWN) weather station located on the research farm.
Experimental Design and Layout
A field experiment was arranged as a randomized complete-block design with
treatments replicated four times. Treatments were a factorial combination of fertilizer
sources (ammonium nitrate (AN) and four CRFs) and fertilizer rates (112, 168 and 224
kg N ha-1) (Table 4-1). Fertilizer treatments were incorporated after banding (15 cm from
seed pieces, 15 cm depth) into potato beds 1 d before planting. Each received 15 kg P
ha-1 and 163 kg K ha-1 prior to planting.
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A major chipping cultivar ‘Atlantic’ in the TCAA was used. Experiment plots were
two rows and each row was 6.1 m long with 1.0 m wide with 1.5 m gap between each
subplot. Every two-rows were also separated by planting two rows of ‘Adora’ potatoes.
The experiment was planted on Feb 22, 2006 and a single row (6.1m) of each plot was
mechanically harvested on June 12, 2006 with a one row commercial harvester
(Middleton Harvester 40, Middleton Harvester Inc, Elkton, FL).
Crop Seasonal Management
Certified seed potatoes were cut into seed pieces (approximately 71 g) and dusted
with fungicide (1.1 g a.i. fludixonil and 21.8 g a.i. mancozeb per 45.4 kg seed pieces;
Maxim MZ, Syngenta Crop Protection, Inc. Greensboro, NC) prior to planting. Seed
pieces were planted at a 102 and 20 cm between and in-row spacing, separately.
Pesticide applications during the season were made according to UF/IFAS extension
recommendations (Hutchinson et al., 2002b). The fungicides were applied as needed
throughout the season for disease control.
Tissue and Water Sampling
Leaf samples were collected 34 days after planting (DAP) then at biweekly
intervals for leaf N analysis. At each sampling date, the eight most recently matured
leaves (expanded) which had reached full size and had turned a dark-green color
(Hochmuth, 1991) were randomly selected to consist of a sample from each plot.
Whole plant samples were collected at full-flower stage. Two plants taken at random
from each plot in the experiments were removed at the soil surface then leaves and
stems were separated. At the same day of harvest, two marketable tubers randomly
selected from each plot, were peeled. The remaining center was then diced into 1 cm
cubes. All tissue samples (leaf, stem and tuber) were then dried at 70 ºC until a
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constant weight was measured, and ground in a Wiley mill (Thomas Scientific,
Swedesboro, NJ) to pass through a 20 mesh sieve, and analyzed for total Kjeldahl
nitrogen (TKN) at the University of Florida’s Analytical Research Laboratory (ARL) using
the standard ARL protocol (Mylavarapu and Kennelley, 2002). Fresh and dry weight of
leaf and stem were recorded at full-flower to calculate total N removal (TNR) of tissues.
N recovery efficiency (NRE) was calculated after the method used by Zvomuya et
al. (2003) by the equation:
NRE = 100 * (Ntreat – Ncontrol) / Napplied (9)
where Ntreat represented the amount of N removed in the tubers of a given fertilizer
treatment, Ncontrol is Nremoved in the tubers of the control plot (no N fertilization), and
Napplied is the amount of N applied as fertilizer. In this study, N recovery efficiency was
calculated as leaf and stem NRE at full-flower stage and tuber NRE at the harvest time.
Water samples were taken at biweekly intervals after herbicide application. A
suction lysimeter (a cylindrical device consisting of a porous ceramic cup) was buried at
30 cm depth below the surface of the potato row for root zone water sampling. A
vacuum of approximately 60 kPa was applied to each lysimeter 24 hours before the
sampling. PVC pipe with holes at the bottom (10 cm diameter by 120 cm long) was
buried at a depth of 100 cm below the soil surface for the perched water table sampling.
The water samples were stored at -5°C and delivered to the University of Florida’s
Analytical Research Laboratory (ARL) analyzed for NO3-N and NH4-N concentrations
using a standard ARL protocol (Mylavarapu and Kennelley, 2002).
Tuber Yield and Quality Analysis
The single row of each subplot was mechanically harvest with commercial
equipment (Middleton Harvester 40, Middleton Harvester Inc, Elkton, FL). Potatoes
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were washed and graded into five size classes as defined by the USDA grading
standards (USDA, 1991). Marketable yield was defined as no. 1 tubers with diameters
between 4.4 and 10.2 cm (USDA, 1978) without visible blemishes (rotten, green,
misshapen, or growth cracks). Culls (green, growth cracks, misshapen, and rotten
tubers) were weighed and reported as a percentage of total yield.
A 20 tuber sub-sample from each subplot was cut into quarters and rated for tuber
internal quality. Visual ratings for tuber internal quality was associated with
physiological disorders including hollow heart (HH), internal heat necrosis (IHN), and
brown center (BC), and presences of disease including, corky ring spot (CRS) and
brown rot (BR). Specific gravity (SG) was measured by the weight in air/weight in water
method (Edgar, 1951).
Statistical Analysis
All statistical analyses (analyses of variance) were performed on each measured
tuber yield and quality variable with main factors of fertilizer source, and fertilizer rate,
and their interaction (SAS Institute 2004). Treatment means were separated using
Duncan’s multiple range test at ρ ≤ 0.05.
Results and Discussion
The 2006 growing season was relative dry (total precipitation of 15.6 cm) and
lower than the historical average of 27.4 cm (Hasting REC Archived Data, 1954-2002).
Only one relatively heavy rainfall (3.38 cm) occurring 4 days after planting (DAP)
(Figure 4-1). The temperature in 2006 was generally favorable for potato growth with
the daily soil temperature all above 15 °C in the early growth season, increasing to 20 to
25°C late in the growing season.
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Tuber Production
Fertilizer source (FS) × fertilizer rate (FS) interaction had no significant influence
on tuber production and size distribution. This suggested that fertilizer sources had a
similar response to increased fertilizer rate, regardless of N source. Main effects of
fertilizer source and rate were significant for total and marketable yields (Table 4-2).
Plants fertilized with AN or H-PCUs produced the highest total tuber yields (36.5 and
36.0 T ha-1, respectively) among fertilizer sources. Plants treated with AN, PSCU+Urea,
and H-PCUs produced the greatest tuber marketable yields at 31.7, 28.9, and 31.4 T
ha-1, respectively. PSCU+Urea and P-PCUs had similar total tuber yield while the MU
treated plants had significantly lower total and marketable yields (30.0 and 25.5 T ha-1,
respectively). MU releases N through microbial decomposition or hydrolysis with
microbial decomposition as the primary release mechanism (Shoji and Kanno, 1994). In
Florida potato production, fumigation is applied approximately 3 weeks prior to planting.
Fumigation may significantly reduce soil microbial population (Morgan et al., 2009). .
MU products with nutrient release depending on microbial activity have limited
applicability for short growing season crops and where soil fumigation practices are
used (Morgan et al., 2009). Similar results of yield reduction have also been reported
for using other types of CRFs with nutrient release through microbial decomposition,
such as sulfured-coated urea (SCU), urea formaldehyde (UF). The release of N from
sulfured-coated urea (SCU) as affected by microbial activity has been reported as
releasing N slowly to sufficiently provide N for Florida potato plants (Maynard and
Lorenz, 1979; Elkashif and Locascio, 1983). Chen et al. (2008) reported potato plants
that were fertilized with UF’s produced significantly lower yields than plants fertilized
with PCUs. The results of these studies suggested that CRFs with nutrient release
74
depending on microbial activity were not appropriate fertilizer sources for Florida potato
production.
Total and marketable yields increased linearly when fertilizer rate increased (Table
2). The increase in fertilizer rate significantly decreased the percentage of A1 and
increased A3 tubers but had no influence on the marketable tuber size B or A2. The
increased N rate provided sufficient N during tuber enlargement, resulting in an increase
in the percentage of size A3 tubers with a decrease in percentage of A1 tubers.
However, N rates greater than 224 kg ha-1 were not evaluated in this study, therefore an
assessment of obtaining the optimal N rate is not possible. Generally, excessive N may
cause tuber yield suppression due to promotion of vegetative growth in the late season
and delay tuber bulking (Westermann and Davis, 1992). Belanger et al. (2000) reported
that quadratic models were the most appropriate method to describe potato yield
response to N rate. For Florida potato production, similar or lower yields were reported
when N rate increased from 224 kg ha-1 to 284 kg ha-1 (Hensel and Locascio, 1987;
Locascio and Hensel, 1990; Martin et al., 1993; Chen et al., 2008). Hochmuth et al.
(1993) also reported that more than 284 kg ha-1 of N frequently decreased potato yields
in the TCAA production area.
Tuber Specific Gravity (SG)
Tuber SG has been used as an indirect method to determine dry matter or starch
content in a tuber. Tuber SG is considered as one important quality character by the
potato chip industry since high tuber SG generally increases quality and yields of chips.
In this study, fertilizer source × fertilizer rate interaction for tuber SG was not significant.
Specific gravity was significantly influenced by either fertilizer source or fertilizer rate
(Table 4-2). Higher SG values leads to higher price from processors. Plants fertilized
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with AN produced tubers with the highest SG (1.080). Plants fertilized with H-PCUs
produced higher SG (1.078) than other CRF treatments. Other studies conducted in
Florida have indicated that plants fertilized with certain CRF products produced similar
tuber SG as compared with AN (Pack et al., 2006; Worthington et al., 2007). A CRF
product with a slower release rate may delay tuber growth and dry matter accumulation
in Florida’s short growing season, resulting in reduced SG. This difference may be
attributed to form of N and CRFs since CRFs release N as urea, urea is then converted
into NH4, and finally NO3 by nitrification. The growth of shoots, roots, and tubers was
greatest with N supplied using an NO3 fertilizer, intermediate with NH4 + NO3, and least
with NH4, for two potato cultivars (Polizotto et al., 1975). Slow conversion times from
CRFs may delay sufficient N supply needed during tuber growth. Zvomuya et al. (2003)
reported similar tuber SG between plants fertilized with urea and PCUs at equivalent N
rate.
Tuber SG linearly increased with increasing N rate. Pack et al. (2006) reported
that tubers grown with 224 kg N ha-1 had significantly greater SG than tubers from the
lower N rate plots within the same fertilizer sources. Martin et al. (1993) reported that
SG increased when N rates increased from 140 to 280 kg ha-1. Though other studies
reported reductions in tuber SG when N rate increased (Westermann and Keinkopf,
1985; Ojala et al., 1990), there was no reduction in tuber SG when N rate increased in
this study since N rate at 224 kg ha-1 did not cause delay in tuber growth, maturation, or
reduce yields. Low SG and high tuber NO3- concentration are more prevalent when
fertilization exceeds the N requirement for maximum tuber yield (Belanger et al., 2002).
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Plants fertilized with CRF treatments produced tubers with the highest SG and
were the highest yielding plants. Similar results were also reported in Florida by Pack,
2004 and Worthington et al. 2006.
External and Internal Tuber Quality
Fertilizer source × fertilizer rate interaction was not significant for tuber external
and internal quality (Table 3). Plants fertilized with P-PCUs produced a significantly
greater percentage of tubers with rot defects than plants fertilized with AN. This may be
attributed to tubers from plants fertilized with P-PCUs were under less protection by
smaller canopy compared to tubers grown with AN treatments, resulting in a higher
percentage of rots due to more exposed tubers. Plants grown with other CRF sources
had similar percentages of tuber external defect as AN treatments. Tubers from plants
fertilized with PSCU+Urea and P-PCUs had a higher percentage of IHN (internal heat
necrosis) than those from AN plots (Table 4-3). The internal defects may be caused by
stressful growing conditions (Hiller et al., 1985). Internal heat necrosis in tubers may
have a relationship with N stress, especially at tuber filling stages (Sterrett and
Henninger, 1997; Sterrett and Heninger, 1991). CRFs differ in their rate of N release.
The PSCU+Urea and P-PCUs treated plots may provide insufficient nutrient levels
which resulted in lower yields as compared with AN. In Florida, Worthington et al.
(2007) reported higher incidence of IHN for tubers grown with CRF than AN. Hutchinson
(2005) and Pack (2004) reported that CRF’s reduced incidence of IHN. This difference
may be attributed to a combination of varying N release rates among CRFs and
different environmental conditions. Tubers fertilized with H-PCUs had a higher
percentage of tuber HH (hollow heart) than those from other fertilizer sources. Fast N
release rates may promote rapid tube growth since N release of PCUs increased with
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higher soil temperatures (Gandeza et al., 1991; Maeda, 1990). The varying release rate
of H-PCUs may cause N stress in the early season due to low soil temperatures then
faster N release late in the season promoting rapid tuber growth. The rapid tuber
enlargement with sufficient soil moisture by seepage-irrigation may result in a high
percentage of hollow heart in tubers fertilized with H-PCUs. High N availability during
tuber bulking with high soil moisture leads to hollow heart (McCann and Stark, 1989).
Leaf Tissue N Analysis
The N content in the leaf tissue can be used as an indirect index measurement to
monitor plant N status. Leaf N at 34 days after planting (DAP) decreased throughout
the growing season for plants treated with each fertilizer source and rate since there
was no additional fertilizer side-dress during the late season (Table 4-4). Wilson et al.,
(2009) also reported a decreasing trend of petiole N as potato plants progressed from
the vegetative stage to tuber bulking stage and maturation stage. The decreasing trend
in petiole N may be attributed to N translocation to the maturing tubers (Ojala et al.,
1990).
Wilson et al. (2009) reported petiole NO3-N concentrations were lower in the early
season but were higher later in the season for plants fertilized with PCUs as compared
with soluble N fertilizers. At 34 DAP, plants fertilized with CRF fertilizers had similar leaf
N content as compared to those fertilized with AN treatments. At 48 DAP, plants
fertilized with MU treatments had significantly lower N concentrations and lower yields
than those fertilized with AN treatments. The N contents in leaf tissue for all fertilizer
sources at 48 DAP (when plants were at 20-25 cm growth stage), were within the
sufficiency range (3.0-6.0%) recommended by UF IFAS (Hutchinson et al., 2009). This
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suggested that N content above critical levels in the early season did not guarantee
maximum tuber yields.
Similar leaf N concentration among fertilizer N rates occurred at 34 DAP. Since N
fertilization was applied once at planting, similar N contents of leaf tissue samples
between plants fertilized with different N rates indicated 50% of BMP N rate applied at
planting can provide sufficient N for early vegetative growth. At low N rate (112 kg N ha-
1), sufficient N for potato growth early in the season may be supplied since minimal N
(approximately less than 15% of required N) was taken up by potato plants before tuber
initiation (Ojala et al., 1990). Hochmuth and Jones (2004) reported that the first N
application can be withheld until plant emergence (14-21 DAP) without yield reduction
for Florida potato production. However, at 48 and 62 DAP, leaf N concentrations were
higher in plants fertilized with 168 and 224 kg N ha-1 than plants fertilized with 112 kg N
ha-1. At 48 DAP (20 to 25 cm growth stage), plants fertilized with 224 kg ha-1 had
significantly greater N concentration than the other fertilizer rates, though N contents
were within sufficiency ranges for all plants. Supplemental N may be applied 30 DAP, if
needed to insure optimum yields. Minimal yield response, to sidedress AN at 40 DAP
was observed after a leaching rainfall at 28 DAP by Worthington et al. (2007). Few
potato roots were observed in the bed shoulder with the majority of the roots within a 25
cm depth from the soil surface (Munoz, 2004). Supplemental soluble fertilizer such as
AN may be more beneficial earlier in the season for rapid plant growth and
development. Higher N contents in leaf tissue from plants fertilized with 224 kg ha-1 may
provide sufficient N to translocate to the developing tubers, resulting in higher yields.
This suggested that tissue N levels in the early season may not provide sufficient
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information to determine N sufficiency of fertilizer sources or rate since the majority of N
was required by plants starting from tuber initiation, triggered by nutrient translocation
from leaf or stem to tubers for optimum yields.
Plant Tissue N Removal (TNR) and Nitrogen Recovery Efficiency (NRE)
At the full-flower growth stage, plants fertilized with AN or H-PCUs had the
greatest N in leaf tissue or leaf + stem tissue (Table 4-5). Plants fertilized with AN had
greater N in stem tissue (10.3 kg ha-1) than plants fertilized with CRFs. Plants fertilized
with H-PCUs also had similar NRE as plants fertilized with AN (Table 4-5). Plants
generally reach the maximum vegetative growth at full-flower growth stage. Higher TNR
in the plant tissue with AN or H-PCUs application was consistent with higher yields.
Therefore H-PCUs provided similar N as did the AN treatment in the early growing
season for optimum tuber yields. Other CRFs may have too slow release rate with
insufficient N release to promote optimal vegetative growth in Florida’s short, cool
growing season. Plants had higher N in leaf, stem, and leaf + stem tissue at the full-
flower growth stage as N rate increased. However, plants fertilized with different N rates
had a similar NRE of leaf + stem at the full flower growth stage. Plant tuber N removal
also significantly increased when fertilizer rate increased but had similar NRE in terms
of N recovery in leaf and stems.
At harvest, the main effects of fertilizer source and fertilizer rate had significant
influence on tuber TNR and tuber NRE (Table 4-5). Plants grown with PSCU and PCU2
had similar tuber TNR (87.9 and 88.4 kg N ha-1, respectively) and tuber NRE (41.5 and
41.2%, respectively) as those fertilized with AN. MU products had the lowest tuber TNR
and NRE attributing to its reduced slow N release rate. Pack et al. (2006) also reported
the low NRE with some CRF’s may be attributed to a “lock-off’ effect inside the fertilizer
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prill leading to improper release rate. Appropriate CRFs need to be evaluated to avoid
potential nutrient loss and water quality adversely affected. Tuber TNR significantly
increased when fertilizer rate increased with the highest TNR 97.1 kg N ha-1 at 224 kg N
ha-1. The plant samples above ground (leaf + stem) were not collected at harvest in this
study since majority of N were tranlocated to tubers. However, plants fertilized with AN
at 224 kg N ha-1 had a TNU in leaf + stem at harvest ranging from 9.4 to 29.0 kg N ha-1
with an average of 17.2 kg N ha-1 (Annual report to St John Water Management, 2009).
More than 50% of the applied N may be recovered at harvest in plants when fertilized
with 224 kg N ha-1. Pack et al. (2006) reported that plants fertilized with AN at 224 kg
N ha-1 at planting recovered 93.5 kg N ha-1 in tubers at harvest. Tuber NRE values
decreased as N rate increased (Table 4-5), which may be attributed to the difference in
N partitioning between plants with or without sufficient N (Grindlay, 1997; Zebarth and
Rosen., 2007). Plants with N deficiency had a greater percentage of N partitioned to the
tubers than N sufficient plants (Millard et al., 1989). This indicated the appropriate N
rate to maximize yields may not result in higher tuber NRE. Sufficient N was important
for extensive canopy development maximizing light inception but may have the potential
to have less percentage N recovered in tubers since excessive N may prolong
vegetative growth period and subsequently delay tuber development.
Water Quality Analysis
Fertilizer source had a significant influence on the perched water table (PWT)
NO3-N concentrations at the 28 day sampling only (Table 4-6). Perched water samples
collected from plots fertilized with AN had significantly higher NO3-N in the early season
(28 DAP) than the CRF sources (Table 4-7). The higher perched water N concentration
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under AN may have attributed to the early N losses. CRFs slowly release N which may
improve synchronized plant N demand.
Low PWT NO3-N concentrations (less than 2.4 mg/L) were measured throughout
the growing season. The concentrations were below the pollution level for nitrate (10 mg
L-1 NO3-N) (USEPA, 2003). Water sampling was not initiated until 28 DAP and
subsequently was not taken in frequent time intervals to obtain meaningful data. The
PVC wells were not installed until after the herbicide application (around 21 DAP) in
study, which was late to monitor any early N leaching. Similar results of low PWT NO3-N
concentration after 34 DAP were reported by Pack et al. (2006). Pack et al. (2006)
reported that the low NO3-N may be also be attributed to the high dilution of nutrients by
the large PWT. However, PWT NO3-N concentration was reported to have a large
variance between years. Munoz et al. (2008) reported that NO3-N concentration was 50
mg L-1 in the PWT during the first and third year of a study while very low NO3-N
concentrations (5 mg L-1) were observed at first sampling date (around sidedress timing,
14 days after plant emergence). The difference was attributed to heavy rainfall between
planting and N side-dressing which leached NO3-N into the soil profile (Munoz et al.,
2008). In this study, a dry season in 2006 with minimal rainfall occurred between
planting to first water sampling date (Figure 4-1). Without leaching early in the season,
low N concentrations were recorded in the PWT.
Soil N Analysis
Critical value (CV) models have been introduced to potato crops to interpret the
critical soil NO3-N levels affecting yields during the growing season (Rodrigues, 2004).
Soil critical values link soil N concentration to yield response to determine whether
yields have either a low or high probability of responsing to supplemental N if soil N
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levels are above or below the CVs. Soil CVs can be considered as an index of soil N
sufficiency. Wilson et al. (2009) demonstrated that CVs may vary among soil types,
fertilizer management practices, climatic patterns, and fertilizer sources. Also, since
tuber yields never were maximized by the N rates used in this study, appropriate CVs
on quadratic model was not able to be developed. The results of soil N analysis were
only used to determine soil inorganic N (NH4-N and NO3-N) availability over the season.
FS × FR interaction was not significant for soil sample N concentration at each
sampling date except for 8 DAP for NH4-N (Table 4-7) and 75 DAP for NO3-N (Table 4-
8). There were similar NH4-N concentrations between soils fertilized with H-PCUs and
soils fertilized with AN from 20 DAP throughout the growing season. NH4-N
concentrations from soil fertilized with other CRFs were lower than soils fertilized with
AN at several sampling times because of their slower release rate. NH4-N
concentrations were higher for soils fertilized with increasing N rate throughout of
season.
However, most soil inorganic N tests for potato production focused mainly on NO3-
N since the NO3-N model was reported as the best method while inclusion of NH4-N had
minimal improvement on the test (Belanger et al., 2001; Rodrigues, 2004). Also, NO3-N
is a more appropriate N form for potato growth than NH4-N regarding optimal potato
growth (Davis et al., 1986). In this study, soil samples from AN treated plots had
significantly greater NO3-N at each sampling date than CRFs. NO3-N concentrations
from soils fertilized with AN were 2-3 time greater than those fertilized with H-PCUs in
the early season (1, 4, and 2.5 times greater at 1, 8, 20 DAP, respectively) and similar
or 1-2 time greater than H-PCUs late in the season (after 34 DAP). CRFs may have
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potential to reduce nutrient losses under heavy rainfall in the early season. The NO3-N
concentrations from soil fertilizer with AN were relatively high in 2006 with minimal
leaching or dilution under a “dry” season. Soil samples from MU treated plots had a
lower NO3-N concentration than soil samples from H-PCUs treated plots, which were
consistent with lower yields from MU plots. Soil NO3-N concentrations increased linearly
with increasing N rates from sampling dates 20 to 75 DAP. Soil NO3-N concentrations
were significantly different at 34 DAP for samples from plots treated with 168 kg N ka-1
and 224 kg N ka-1 (75% and 100% of current BMP N rate). Perhaps applying a third of
N in a split application around 30 DAP would minimum yield losses while reducing
potential N loss. Sidedress fertilizer is surface applied then covered with soil at hilling to
avoid root damage. Soil incorporated fertilizer applied at planting resulted in
insufficiently use by the potato root system (Munoz et al., 2008). The optimal use of the
sidedress application may either use liquid fertilizer placed near potato roots or
overhead irrigate to move nutrients to the potato root zone.
Plants fertilized with PSCU and H-PCUs had comparable marketable yields to
plants fertilized with soluble AN and merit further evaluation while plants fertilized with
MU had low yields due to the material’s slow release rate under Florida’s environment.
Polymer coated fertilizers are improved fertilizers for use in Florida potato production in
the TCAA than other CRFs. The reduction in tuber quality due to nutrient stress
occurred in plots with CRF application as compared with AN application. An
improvement of nutrient use efficiency was not measured by using the CRFs because of
insufficient N release and minimal leaching during growing season. Manufacturers may
alter the coating material or thickness of these two CRF for a quicker release rates.
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Further use of the CRF’s may also require use of some soluble fertilizers in order to
insure N availability throughout the potato growing season in North Florida.
Minimal N occurred in the perched water table due to insufficient sampling timing
and low rainfall during the sampling period. Evaluation of water quality daily throughout
the entire growing season is extremely important in order to determine the influence of
CRFs to reduce N leaching.
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Table 4-1. Fertilizer treatments, manufacturers, and rates evaluated in Hastings, FL, in 2006z. Fertilizer sourcey Manufacturer Formulationx Grower Standard (AN) Gator Fertilizer 34-0-0 (ammonium nitrate) Scotts Potato Blend (PSCU+Urea) Scott Chemical Co. 86% coated 38-0-0 (PSCU), 14% urea
PTI Triple Blend (P-PCU) Purcell Technologies, INC 20% 44.5-0-0, 40% 44-0-0, 40% 43-0-0 (all PCUs) Haifa Double Blend (H-PCU) Haifa Chemicals 50% 42-0-0 , 50% 40-0-0 (all PCUs) Super Rainbow/Nitamin (MU) Georgia Pacific 23-0-0 (MU)
z Each fertilizer source was applied at 112, 168 and 224 kg N ha-1. yPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; MU: methylene urea; AN: ammonium nitrate. xPercent N-P2O5-K2O
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Table 4-2. The influence of fertilizer source and fertilizer rate on ‘Atlantic’ tuber yield, size distribution, and tuber specific gravity (SG), in Hastings, FL in 2006.
Total Marketable Size yield yieldz Distribution by class (%)y
Main effects (T ha-1) (T ha-1) B A1 A2 A3 Specific gravity
Fertilizer source (FS) AN 36.5 a 31.7 a 4.4 b 58.6 ab 24.5 a 11.6 bc 1.080 a PSCU+Urea 33.9 b 28.9 ab 3.9 b 51.9 bc 26.1 a 17.1 ab 1.076 c P-PCUs 33.5 b 28.0 b 4.0 b 53.4 bc 27.7 a 13.9 a-c 1.076 c H-PCUs 36.0 a 31.4 ab 4.0 b 48.5 c 27.8 a 18.6 a 1.078 b MU 30.0 c 25.5 c 7.0 a 64.6 a 17.6b 9.7 c 1.076 c Fertilizer rate (FR) (kg N ha-1) 112 29.8 21.6 5.3 63.1 22.5 7.9 1.076 168 34.1 29.3 4.7 54.6 26.2 13.5 1.077 224 38.0 32.7 4.1 48.6 25.4 21.1 1.079 L**w L** L** L* L* Interaction FS*FR NS NS NS NS NS NS NS
zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. yPercent of total yield: 4.4cm ≥ B classes ≥ 3.8 cm; 6.4 cm≥ A1 ≥ 4.4 cm; 8.3 cm≥ A2 ≥ 6.4 cm; 10.2 cm ≥ A3 ≥ 6.4 cm. x Means separated within columns by Duncan’s multiple range test, p ≤ 0.05. wL = linear. NS, *, ** Nonsignificant or significant at the p ≤ 0.05 and 0.01 levels, respectively.
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Table 4-3. The influence of fertilizer source and rate on ‘Atlantic’ potato tuber percent external and internal tuber defect (%) of total yield, in Hastings, in FL 2006.
% External Tuber Defects % Internal Defectsy
Growth Mis- Green Rot Total Brown Center
Main effects cracks shapen cullsz HH BR CRS IHN L M H
Fertilizer source (FS)
AN 0.5 0.7 1.8 6.5 bcx 9.5 ab 0.0 b 0.0 0.0 1.7 b 0.0 0.0 0.0PSCU 0.4 0.9 1.3 8.8 ab 11.3 ab 0.0 b 0.0 0.0 10.4 a 0.0 0.0 0.0PCU1 0.3 0.4 1.7 10.1 a 12.5 a 0.0 b 0.0 0.0 10.8 a 0.0 0.0 0.0PCU2 0.1 0.4 1.9 8.7 a-c 11.0 ab 1.6 a 0.0 0.0 6.3 ab 0.0 0.0 0.0MU 0.3 0.5 1.6 5.2 c 7.6 b 0.0 b 0.0 0.0 2.1 b 0.0 0.0 0.0Fertilizer rate (FR) (kg N ha-1)
112 0.3 0.6 1.1 9.8 11.9 0.0 0.0 0.0 7.0 0.0 0.0 0.0
168 0.3 0.4 1.8 6.8 9.3 0.8 0.0 0.0 4.5 0.0 0.0 0.0
224 0.3 0.7 2.1 7.0 10.1 0.3 0.0 0.0 7.3 0.0 0.0 0.0Interaction FS*FR NS NS NS NS NS NS NS NS NS NS NS NS
zTotal culls are the sum of green, growth cracks, misshaped, rotten categories and are calculated as a percent of total yields yHH, hollow heart; BR, brown rot; CRS, corky ring spot; IHN, internal heat necrosis. Brown Center: L = Light, M = Moderate, H = Heavy xMeans separated within columns by Duncan’s multiple range test, ρ ≤ 0.05. NSNonsignificant.
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Table 4-4. The effects of fertilizer source and fertilizer rate on ‘Atlantic’ potato leaf N concentration (% of tissue dry weight), in Hastings, FL, in 2006.
Days after planting Main effects 34 48 62 76
Fertilizer source (FS) --------------------(%)--------------------- AN 5.1 abz 4.7 b 3.9 a 2.9 ab PSCU 4.8 b 4.7 b 3.7 b 3.1 a PCU1 5.0 ab 4.8 b 3.6 b 3.0 a PCU2 5.3 a 5.0 a 3.8 ab 2.7 b MU 5.0 ab 4.4 c 3.3 c 2.4 c Fertilizer rate (FR) (kg N ha-1) 112 4.9 4.5 3.4 2.7 168 5.0 4.8 3.9 2.7 224 5.1 5.0 3.7 3.0 L**y Q** Interaction FS*FR NS NS * NS
zMeans separated within columns by Duncan’s multiple range test, ρ ≤ 0.05. yL = linear and Q = quadratic. NS, *, ** Nonsignificant or significant at the p ≤ 0.05 and 0.01 levels, respectively.
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Table 4-5. The plant tissue N removal (TNR) and N recovery efficiency (NRE) of ‘Atlantic’ potato on a per-hectare basis when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006.
Full flower GS Harvest Leaf N Stem N Leaf + stem Leaf + stem Tuber TNR Tuber
Main effects (kg ha-1) (kg ha-1) (kg ha-1) NRE (%) (kg ha-1) NRE (%)
Fertilizer source (FS)
AN 37.0 az 10.3 a 47.3 a 26.3 a 90.4 a 42.3 a PSCU+Urea 27.2 c 5.1 c 32.3 b 16.4 bc 87.9 a 41.5 a P-PCUs 28.4 bc 4.9 c 33.3 b 17.5 bc 78.5 b 34.9 b H-PCUs 34.0 ab 7.2 b 41.2 a 21.5 ab 88.4 a 41.2 a MU 23.1 c 4.7 b 27.8 b 13.3 c 65.3 c 27.0 c Fertilizer rate (FR) (kg N ha-1) 112 23.2 4.6 27.7 20.3 67.3 41.6 168 28.2 5.7 33.8 17.2 81.9 36.4 224 38.5 9.0 47.5 19.3 97.1 34.1 L*y L* L* L** L** Interaction FS*FR NS NS NS NS NS NS
zMeans separated within columns by Duncan’s multiple range test, ρ ≤ 0.05. yL = linear effect. NS, *, ** Nonsignificant or significant at the p ≤ 0.05 and 0.01 levels, respectively.
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Table 4-6. The water sample NH4-N and NO3-N concentrations (mg L-1) at perched water table for ‘Atlantic’ potato grown under fertilizer source and fertilizer rate treatments in Hastings, FL, in 2006.
Days after planting
NH4-N (mg L-1) NO3-N (mg L-1) Main effects 28 42 56 70 84 96 28 42 56 70 84 96
Fertilizer source (FS) AN 1.7 0.6 0.5 0.4 0.3 0.2 2.4 az 0.6 0.3 0.3 0.3 0.3 PSCU+Urea 1.0 0.4 0.5 0.4 0.4 0.3 0.7 b 0.5 0.4 0.3 0.2 0.3 P-PCUs 1.1 0.6 0.4 0.3 0.3 0.3 0.3 b 0.2 0.5 0.5 0.3 0.3 H-PCUs 1.2 0.7 0.4 0.4 0.3 0.2 0.4 b 0.2 0.4 0.4 0.4 0.4 MU 1.2 0.6 0.6 0.4 0.3 0.3 0.4 b 0.1 0.2 0.3 0.3 0.3 Fertilizer Rate (FR) (kg N ha-1) 112 1.1 0.5 0.4 0.3 0.3 0.2 0.8 0.3 0.3 0.3 0.3 0.3 168 1.1 0.5 0.5 0.4 0.3 0.2 0.7 0.3 0.3 0.3 0.2 0.3 224 1.4 0.8 0.6 0.5 0.4 0.3 1.0 0.3 0.5 0.4 0.4 0.4 Interaction FS*FR NS NS NS NS * NS NS NS NS NS NS NS
zMeans separated within columns by Duncan’s multiple range test at ρ ≤ 0.05. NS, * Nonsignificant or significant at the p ≤ 0.05.
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Table 4-7. The soil sample NH4-N concentrations (mg kg-1) at perched water table for ‘Atlantic’ potato when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006.
Days after planting
Main effects 1 8 20 34 48 62 75 89
Fertilizer source (FS) -----------------------------------------------mg kg-1-------------------------------------------------- AN 10.5 az 25.6 a 20.1 a 14.0 a 7.9 8.4 8.4 b 14.0 a PSCU+Urea 6.6 b 15.1 b 12.6 b 9.6 bc 8.6 8.4 13.7 a 12.1 ab P-PCUs 6.4 b 10.5 b 13.4 b 10.4 a-c 7.2 8.3 12.7 a 9.8 b H-PCUs 6.6 b 12.9 b 16.4 ab 13.4 ab 7.3 10.2 14.5 a 13.6 a MU 9.0 ab 21.2 a 20.3 a 8.8 c 6.9 8.6 13.5 a 10.7 b Fertilizer rate (FR) (kg N ha-1) 112 7.60 14.3 13.6 8.9 6.6 6.9 9.6 9.7 168 7.80 16.8 16.5 10.5 6.7 9.0 12.6 12.5 224 8.10 20.1 19.5 14.4 9.4 10.5 15.2 13.9 L*y L** L** L** L** L** L** Interaction
FS*FR NS * NS NS NS NS NS NS zMeans separated within columns by Duncan’s multiple range test at ρ ≤ 0.05. yL = linear effect. ns, *, ** Nonsignificant or significant at the p ≤ 0.05 and 0.01 levels, respectively.
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Table 4-8. The soil sample NO3-N concentrations (mg kg-1) at perched water table for ‘Atlantic’ potato when grown under several fertilizer sources and fertilizer rates in Hastings, FL, in 2006.
Days after planting
Main effects 1 8 20 34 48 62 75 89
Fertilizer source (FS) ----------------------------------------------mg kg-1--------------------------------------------------- AN 12.0 az 42.3 a 54.1 a 68.2 a 40.0 a 28.8 a 40.8 a 53.3 a PSCU+Urea 3.4 b 11.2 b 22.7 b 33.6 cd 19.8 c 16.7 bc 26.7 b 21.7 bc P-PCUs 1.7 b 8.0 b 14.0 c 38.6 bc 20.9 c 18.6 b 25.4 b 20.2 bc H-PCUs 2.2 b 10.2 b 21.2 b 47.0 b 29.5 b 25.8 a 30.7 b 31.3 b MU 2.2 b 7.9 b 20.7 b 28.5 d 14.5 c 10.7 c 14.6 c 11.7 c Fertilizer rate (FR) (kg N ha-1) 112 4.5 13.8 21.5 32.5 17.8 12.5 18.7 18.7 168 4.7 16.0 27.0 44.3 23.1 20.6 27.1 28.2 224 3.7 18.0 31.1 52.8 33.9 27.1 37.1 36.0 L**y L** L** L** L** L** Interaction
FS*FR NS NS NS NS NS NS * NS zMeans separated within columns using Duncan’s multiple range test at ρ ≤ 0.05. yL = linear effect. ns, *, ** Nonsignificant or significant at the p ≤ 0.05 and 0.01 levels, respectively
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Figure 4-1. Average daily 60 cm air temperature(C°), 10 cm depth soil temperature (C°) and daily rainfall (cm) during growth season in Hastings, FL, in 2006. The filled triangles denote planting and harvesting dates.
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CHAPTER 5 EVALUATION OF ALTERNATIVE FERTILIZER PROGRAMS FOR NORTHEAST
FLORIDA POTATO PRODUCTION
Introduction
St. Johns, Putnam, and Flagler counties comprise the Tri-County Agricultural Area
(TCAA) in northeast Florida. The TCAA supports approximately 11,330 ha of irrigated
agricultural production of potato, cabbage and other crops. The area accounts for 65%
of the statewide potato production (Livingston-Way, 2007). “Best Management
Practices” have been implemented for potato production in the TCAA to reduce the
potential for nitrate movement into subsurface water. Seepage irrigation is used in this
area for potato production to maintain a perched water table between 45 cm and 60 cm
below the surface of the bed (Hutchinson et al., 2002a). Controlled release fertilizers
(CRFs) are one potential component of local BMPs that slowly release nutrients
therefore reduce the potential for nutrient leaching into the watershed.
CRFs are formulated to provide nutrients to plants over time at quantities
synchronizing with plant demand. One major category of CRF is the coating fertilizers
with a water insoluble coating around a soluble fertilizer core to prevent nutrient
solubility. The common coating materials used in CRFs are sulfur, polymer and some
combinations of these materials (Morgan et al., 2009). However, sulfur coated ureas
(SCUs) have been reported to not sufficiently release N to meet the demands of Florida
potato crops (Maynard and Lorenz, 1979; Elkashif and Locasicio, 1983). Polymer-
coated fertilizers represent one of the major coating fertilizers with more predictable
nutrient release than SCU (Shoji and Gandeza, 1992; Shaviv, 2000). Polymer coated
urea (PCU) is the urea fertilizer coated with a polymer coating film, which is typically
composed of a blend of water permeable and impermeable resins and surfactants
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(polyolefin or polyethylene), ethylene, vinyl acetate, and talc occurring as layered plates
(Shoji, 1999). Most PCUs release N by water diffusion through a semipermeable
membrane composed by either thermost resin or thermoplastic resin coatings.
Differences in composition and thickness of the coating material results in varying
release rates. Under field conditions release rate of N from PCUs are affected by
several environmental factors including soil temperature and soil moisture. Generally,
soil temperature is the primary factor governing N release rate (Gandeza et al., 1991).
However, since polymers are relatively expensive materials, the combination coatings of
sulfur and polymer have been considered to offset the cost. Polymer-sulfur coated urea
(PSCU) consists of a sulfur-coated urea prill encapsulated by a polymer coating.
Nitrogen release of PSCU is through a combination of diffusion and capillary actions.
PSCUs can be less expensive to produce than a traditional polymer coated urea but
offer a great degree of control over nutrient release.
Zvomuya and Rosen (2001) reported that ‘Russet Burbank’ potatoes grown with
PCU (applied at planting) on a sandy soil in Minnesota produced higher marketable
yields than a urea treatment (applied at emergence and hilling) at fertilizer rates ranging
from 110 to 290 kg N ha-1. Zvomuya et al. (2003) reported that at a N rate of 280 kg N
ha-1, NO3-N leaching was 34 to 49% lower with PCU treatments than three split
applications of urea while nitrogen recovery efficiency (NRE) for PCU averaged 50%,
7% higher than urea treatments (43%). In Florida, Hutchinson (2005) reported no loss in
potato yield and quality using a CRF program at 196 kg N ha-1 as compared with the
traditional fertilizer program at of 224 kg N ha-1 soluble fertilizer. Hutchinson (2005)
reported that plants grown with PSCU at 168 kg N ha-1 produced significantly greater
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tuber total and marketable yields (45.8 and 29.0 T ha-1, respectively) than potatoes
grown with ammonium nitrate (AN; NH4NO3) at the same N rate. Pack et al. (2004)
reported that tubers from plants grown with PSCU fertilizer had a 68% reduction of
internal heat necrosis (IHN) as compared with a standard AN based fertilizer program.
However, the high cost per nutrient unit has been the primary factor that limit the
widely acceptance of CRF application (Trenkel, 1997; Zvomuya and Rosen, 2001).
Currently, a new PCU (440 g N kg-1) called ESN (Environmentally Smart Nitrogen)
developed by Agrium Inc and PSCU (380 g N kg-1) developed by Scotts LLC have
shown promising results for application in potato production with considerably lower in
price (Hopkins et al., 2008; Wilson et al., 2009; Worthington, et al., 2007). Evaluation of
the commercial application potential of these two CRFs for Florida potato production is
needed. The optimal application timing of these two CRFs has not been investigated.
Use of PSCUs or PCUs alone may not provide sufficient early season nutrient release
at a rate required for rapid early growth. The need for side dressing and the need for
conventional soluble fertilizers for optimal growth are not know for Florida production
systems. Also, the short growth season in Florida is another challenge because the
slow release characters of CRFs may limit a rapid growth response of plants (Guertal,
2009). The application of CRF prior to planting may provide an alternative application
time and extend release period synchronizing high N demand of potato plants during
late season.
Potato cultivars may differ in their N uptake profile due to differential growth rates
and N requirements. Optimal N fertilizer management needs to match plant N need to
maximize tuber yield and quality. The standard chipping cultivar ‘Atlantic’ has good
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yield potential, but tubers are susceptible to internal heat necrosis (IHN) resulting in
unmarketable tubers (Henninger et al., 1979). New potato cultivars such as ‘Harley
Blackwell’ and FL 2053 (a Frito-Lay cultivar) have been reported to be more resistant to
IHN (Hutchinson et al., 2006). These new cultivars have vigorous growth and their
nutrient requirements in the TCAA are unknown.
The objectives of this research were to 1) evaluate potato production, tuber
quality, and nutrient use efficiency response to CRF source and application timing; 2)
evaluate optimal fertilizer application program for ‘Atlantic’, ‘Harley Blackwell’ and
‘FL2053’.
Materials and Methods
The study was conducted at the University of Florida’s Partnership for Water,
Agriculture, and Community Sustainability Farm, Hastings, FL in 2007 and 2008. Soil
was an Ellzey fine sand (sandy, siliceous, hyperthermic Arenic Ochraqualf; sand 90-
95%, <2.5% clay, <5% silt).
Treatments were arranged in a split-plot experimental design with four replications.
The main plot factor was fertilizer treatment and the sub-plot was cultivar. Each main
plot contains three sub-plots with 1.52 m distance between each sub-plot. The sub-plots
were four rows wide (100 cm between rows) by 6.1m long. Seed spacing within-row
was 20 cm.
Fertilizer treatments were the combination of fertilizer source (PSCU and PCU)
(Table 5-1) and application timing (Table 5-2). Application timing was at fumigation (21
days prior to planting), preplant (one day prior to planting), hilling (10 days after
emergence), and a combination of application timings (Table 5-2). All CRF N rate was
at N rate of 196 kg ha-1. All plots received 15 kg P ha-1 and 163 kg K ha-1 prior to
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planting. The fertilizer applications prior to planting were soil incorporated while
applications at hilling were in row banded and covered with soil to avoid root damage.
Production Management
Certified seed potatoes were cut into seed pieces (approximately 71 g each) and
dusted with fungicide (1.1 g a.i. fludixonil and 21.8 g a.i. mancozeb per 45.4 kg seed
pieces; Maxim MZ, Syngenta Crop Protection, Inc. Greensboro, NC) prior to planting.
Potato seed pieces were planted and harvested on 5 Mar. and 11 Jun. 2007; 6-7 Feb
and 27-28 May. 2008, respectively. Pesticide applications during the season were made
according to the UF extension recommendations (Hutchinson et al., 2002b). Weather
data were collected and recorded with the Florida Agricultural Weather Network weather
station located on the research farm. Seepage irrigation was used with a perched water
table maintained of 45-60 cm below the top of the potato row during the season.
Measurement during the Growing Season
At the 20-25 cm growth stage, the leaf samples were collected for tissue N
concentration analysis. The eight most recently matured leaves (expanded) which had
reached full size and had turned a dark-green color (Hochmuth, 1991) were randomly
selected to consist of a sample for each plot. The leaf sampling was only taken from the
two center rows of each plot. The leaf samples from each plot were dried at 70º C
(generally 7 days) until a constant weight was measured (weight difference within 0.1 g
after drying for 24 hrs). Leaves were then ground in a Wiley mill (Thomas Scientific,
Swedesboro, NJ) to pass through a 20 mesh sieve, and analyzed for total Kjeldahl
nitrogen (TKN) at the University of Florida’s Analytical Research Laboratory (ARL).
At full-flower stage, two plants taken at random from each plot in the experiments
were removed at the soil surface. Tubers of these two plants were collected and fresh
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weights were recorded. Leaves and stems were separated, dried until a constant weight
was measured (weight difference within 0.1 g after drying for 24 hrs), and ground in a
Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass through a 20 mesh sieve, and
analyzed for TKN at the ARL (Mylavarapu and Kennelley, 2002). Two marketable
tubers randomly selected from each plot were peeled. The remaining center was then
diced into 1 cm cubes, dried until a constant weight was measured (weight difference
within 0.1 g after drying for 24 hrs) and ground in a Wiley mill (Thomas Scientific,
Swedesboro, NJ) to pass through a 20 mesh sieve. Tuber samples were analyzed for
TKN at the ARL using standard procedures (Mylavarapu and Kennelley, 2002). Total
Kjehldahl N measured organic nitrogen (N); ammonia (NH3) and ammonium (NH4+) in
the chemical analysis. Since most N in the leaf, stem or tuber were in chemical
compounds in chlorophyll, amino acids, proteins, and nucleic acids. TKN values were
used to an approximate measurement of tissue total N contents. The fresh and dry
weight of leaf, stem, tubers, and diced tuber tissue were recorded and used to calculate
N use efficiency.
Water samples were taken at biweekly intervals after herbicide and last fertilizer
applications. PVC pipe with holes at bottom (10 cm diameter by 120cm long) was buried
at a depth of 100 cm below the soil surface for the perched water table sampling. The
water samples were stored at -5°C and delivered to the University of Florida’s Analytical
Research Laboratory (ARL) analyzed for NO3-N and NH4-N concentrations using a
standard ARL protocol (Mylavarapu and Kennelley, 2002).
The soil samples were taken from each plot: prior to planting, 20-25cm, full-flower,
and harvest growth stages. The N concentrations in soil samples at these timing were
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used to interpret N levels before fertilization, N sufficiency for potato vegetative growth,
tuber developing, and soil residual after harvesting, respectively. At each sampling time,
the composite sample of eight 15 cm depth cores were taken on hill from the center two
beds of each plot, then air-dried and sieved, and sent to the University of Florida’s ARL
for NH4-N and NO3-N concentrations using a standard protocol (Mylavarapu and
Kennelley, 2002).
The center two rows of each plot were mechanically harvested by a one row
commercial harvester (Middleton Harvester 40, Middleton Harvester Inc, Elkton, FL).
Potato tubers were washed and graded into six size classes using a commercial
grading machine according to USDA grading standards (USDA, 1991). Marketable yield
was defined as U.S. No. 1 tubers with diameters between 4.4 and 10.2 cm (USDA,
1991) without visible blemishes (rotten, green, misshapen, or growth cracks). Specific
gravity (SG) was measured by the weight in air/weight in water method (Edgar, 1951).
Culls (green, growth cracks, misshapen, and rotten tubers) were weighed and reported
as a percentage of total yield. A 20 marketable tuber sub-sample from each subplot was
cut into quarters and rated for tuber internal quality. The visual rate for tuber internal
quality was mainly on physiological disorders including hollow heart (HH), internal heat
necrosis (IHN) and brown center (BC) and disease including, corky ring spot (CRS) and
brown rot (BR).
At harvest, two marketable tubers were randomly selected from each plot and
peeled. The center of the peeled tuber was then diced into 1 cm cubes, dried, and
ground. Tuber samples were analyzed for TKN at the ARL using standard procedures
(Mylavarapu and Kennelley, 2002). Nitrogen recovery efficiency (NRE) reflects the
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amount of applied N recovered from the field in tubers. NRE was calculated after the
method used by Zvomuya et al. (2003) by the equation (9) that described previously. In
this study, NRE was calculated as the tuber NRE at harvest.
Statistical Analysis
Combined analyses of variance (ANOVA) among years (2007 and 2008) indicated
significant treatment and year interactions. This may have been attributed to the
different growing condition (such as planting date, rainfall, temperature, etc) in each
year. Therefore, separate ANOVA’s for each year was conducted to evaluate influence
of the CRF source, application timing, and their interactions on potato production and
water quality. Likewise, N fertilizer management may differ for each cultivar. Therefore
the data from each cultivar were analyzed separately. All data were subjected to
analysis of variance using SAS general linear model to evaluate main and interaction
effects (SAS Institute, 2004).
Results and Discussion
‘Atlantic’
Tuber production and quality
‘Atlantic’ has been the standard chip cultivar in the TCAA with relatively high yield
and high tuber specific gravity (SG) after its release in 1976 by USDA. ‘Atlantic’
replaced ‘Sebago’ as the primary chipping potato in the TCAA with light color
processing quality because of its advantage of high yields and high tuber SG. The
planting date (March 5) in 2007 was considered as a late planting in TCAA potato
production with relatively high temperature and rapid growth in the early season. The
level of precipitation during growing season (17.95 cm) was lower than the historical
average of 27.41cm in Hastings area (Pack et al., 2006).
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In 2007, plants fertilized with PSCU produced significantly greater total and
marketable yields than plants fertilized with PCU if both were applied with two split
application (137 and 59 kg N ha-1 at fumigation and preplanting, respectively) (Table 5-
3). Plants fertilized with PSCU produced similar total and marketable yields as plants
fertilized with PCU if applied preplanting or with three split applications (96, 41 and 59
kg N ha-1 at fumigation, preplanting and hilling, respectively). This indicated the
advantage of PSCU over PCU for early application at fumigation combined with
preplanting timing to synchronize ‘Atlantic’ potato N demand. Also, PSCU provided
more flexible application timings because its N release was less temperature sensitive
most PCU products (Sartain, 2004). The N release of PCU was mostly depending on
soil temperature instead of soil moisture (Sartain, 2004; Chen et al., 2008). The yield
differences between plants PSCU and PCU were eliminated when both 100% applied
preplanting or applied with three split applications (at fumigation, preplanting and with
AN sidedress at hilling). These results suggested that application of PCU to optimal
yields in Florida needs to consider initial soil temperatures. Minimal benefits on tuber
yields were realized by sidedressing partial N using AN at hilling (approximate 10 day
after emergence). This suggested preplanting PSCU or PCU at 196 kg ha-1 may provide
sufficient N in the early season. Also, the current practice in TCAA of soluble N
sidedress at hilling was surfaced applied with soil cover in TCAA to avoid root damage
whereas N application at fumigation or planting was soil incorporated (Munoz, 2008).
Without rainfall, potato plants may response slowly to supplemental AN (Worthington et
al., 2007; Munoz, 2008). There was only few rain events (each was less than 0.5 cm a
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day) after AN sizedress until a 2 cm rainfall at 9 days after sidedress (Figure 5-1-a),
which may prevent the rapid plant response to the sideress AN.
The yields in 2008 were generally much lower than in 2007, lower than the 10
year average commercial potato yields (1997-2006) around Hasting area (31.9 T ha-1)
(USDA, 2007). The difference of yields between 2007 and 2008 can be attributed to
increased rainfall at critical potato growth stages in 2008. For example, a 8 cm rainfall in
a day at 30 DAP and another 7 cm in 3 days from 57-60 DAP (Figure 5-1-b). This
indicated the leaching events, as defined as 7.6 cm in 3 days or 10.0 cm in 7 days
(Kidder et al., 1992). There were similar total and marketable yields between plants
fertilized with PSCU and PCU applied with same method. PSCU and PCU were
reported to be CRFs with fast N release with estimated 90 release period (Worthington
et al., 2007; Wilson et al., 2007). The fast N release of PSCU or PCU in early season
also increased the risks of nutrient loss. The additional soluble N application may also
need to minimize yield losses under leaching events during growing season. In this
study, the heavy rainfall in early season eliminated the difference of N supply between
different CRF sources or fertilizer timing, resulting in similar yields.
Tuber SG is as an indirect measurement to determine dry matter or starch content
in a tuber. The high tuber SG is desirable for processing potatoes because of improved
production efficiency. Generally, tuber with higher SG values may increase the
opportunity for growers to have a premium price according to the purchase contract
between growers and the potato chip industry. Growers in TCAA products have the
incentives to conduct those alternative cultural practices to improve tuber SG for
contract potato production. In 2007, there were similar tuber SG values between plants
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fertilized with PSCU and PCU applied with same method. Tuber SGs were higher than
1.081 (Table 5-3), which was higher than the averaged SG (1.079) for ‘Atlantic’ potatoes
at University of Florida Hasting research farm (Hutchinson et al., 2002). In 2008, plants
fertilized with PSCU produce similar tuber SG as PCU if both were applied preplanting.
Plants fertilized with PCU had greater tuber SG than PSCU if applied with two split
applications (137 and 59 kg N ha-1 at fumigation and preplanting, respectively) or with
three split applications (96, 41 and 59 kg N ha-1 at fumigation, preplanting and hilling,
respectively). This may attributed to faster N release at late season for PCU when soil
temperatures were high. Plants fertilized with PCU in the early season were able to
partition more N for tuber development than PSCU, resulting in higher dry matter
content.
In 2007 and 2008, plants fertilized with PSCU and PCU had similar on tuber size
distribution if applied in the same method, which may be attributed to same N rate was
used for each treatment. Also, plants fertilized with PSCU and PCU had minimal
significant differences for tuber external and internal quality if applied with same
application timing.
Tissue nutrient analysis
The tissue N levels at potato 20-25 cm and full-flower stages are commonly used
as the indicator of plant crop N status (Hutchinson et al., 2009). The sufficiency ranges
for potato 20-25 cm and full-flower range were recommended at 3.0-6.0% and 3.0-4.0%
of dry weight basis, respectively (Hochmuch et al., 2001).
In 2007, leaf tissues sampled at potato 20-25 cm growth stage from plants
fertilized with PSCU had similar N concentrations as plants fertilized with PCU if both
applied preplanting or with two split applications (137 and 59 kg N ha-1 at fumigation
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and preplanting, respectively) (Table 5-8). However, leaf tissues from plants fertilized
with PSCU had significantly lower N concentrations than PCU if applied with three split
applications (96, 41 and 59 kg N ha-1 at fumigation, preplanting and hilling,
respectively). Leaf tissue N concentrations sampled at potato 20-25cm growth stage
were above sufficiency range (>6% dry weight basis but %) except leaf tissue N
concentration sampled from plants fertilized with (PSCU+AN)2 were 5.7% (Table 5-5),
within the sufficiency range. This suggested that PSCU or PCU treatments provided
sufficient N in the early season, resulting in the minimal benefits on yields by
sidedressing with AN at hilling. Generally, it was reported that plants with tissue N
values above sufficiency range indicated over application, which may result in yield
suppression (Hochmuth et al., 1991). However, it was also reported in TCAA that N
values above the sufficiency range in the early season produced greater yield
(Hochmuth and Cordasco, 2000). Pack (2004) reported that leaf tissue samples taken
from plants whose leaf tissue N were high in the early season and were within the
sufficiency ranges during the late season did not result in yield losses. The early
diagnosis of N sufficiency was more important to direct fertilizer management especially
when leaf tissue N concentrations were below the N sufficiency range. The additional N
application to correct N deficiency needs to be applied prior to potato full-flower stage in
Florida potato production. Any fertilizer practices (sizedress or overdress) close to full-
flower stage would not increase tuber yields due to a short growing season (Hutchinson
et al., 2009; Hochmuth and Cordasco, 2000).
Leaf tissue N concentrations sampled at full-flower growth stage were also above
adequate sufficiency range (above 4% dry weight basis) for plants fertilized with all
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treatments except (PCU+AN)1 (Table 5-5). There were similar leaf tissue N
concentrations between plants fertilized with PSCU and PCU applied with the same
method. It was reported in the TCAA area, plants fertilized with N rate greater than 168
kg ha-1 generally reflected adequate N concentrations in leaf tissue (Hochmuth and
Cordasco, 2000). There were also no significant differences for tuber tissue N
concentrations at full-flower stage. With minimal leaching force in 2007, plants fertilized
with both CRF sources (PSCU and PCU) did not show inadequate N supply for early
potato growth. At full-flower growth stage, plants uptake similar N in tissue leaf+stem
tissue per hectare basis for PSCU and PCU if applied with same method. At full-flower
stage, plants can uptake 56.9 to 91.1 and 28.2 to 49.7 kg N ha-1 in vine (leaf+stem) and
tuber tissues, respectively(Table 5-5). This suggested an approximately an average of
115.4 kg ha-1, 59% as applied N rate was in plant majority issues (leaf, stem and tuber)
at full-flower stage.
At harvest stage, there were similar total N uptakes (TNUs) between plants
fertilized with PSCU and PCU applied with the same method. ‘Atlantic’ potato plants
recovered 96.8 kg N ha-1 averaged over fertilizer treatments, double amount of as tuber
TNU at full-flower stage. The majority of N at this stage was translocated from leaf+stem
to tubers and tubers were the final products harvested from field (Ojala et al., 1990).
The accumulated high N in early season was important in late growth stage for plants
with high N demand for tuber development (Hochmuth and Cordasco, 2000).
Unfortunately, plant leaf and stem tissues were not sampled at harvest timing in this
study in order for an estimation of total plant N recover. In another study conducted in in
Hastings research farm, plants fertilized with AN at 224 kg N ha-1 have a TNU in leaf +
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stem at harvest ranging from 9.4 to 29.0 kg N ha-1 with a average 17.2 kg N ha-1
(Hutchinson and Beyer, Annual Report to St John Water Management, 2009). It can be
estimated that total N uptake (TNU) in plants were around 114 kg ha-1 averaged over
fertilizers. The tuber nitrogen recovery efficiencies (NRE) were similar between plants
fertilized with PSCU and PCU with an average of 36.0% if applied with same application
timings. This average NRE fell in the tuber NRE range (34.5 to 49.3%) at harvest from
another study for Atlantic’ potatoes fertilized with various CRFs in Florida (Pack, 2004).
The similar NRE between fertilizer treatments suggested similar N use efficiency in
season between PSCU and PCU at 196 kg N ha-1.
In 2008, there were similar leaf N concentrations sampled at 20-25 cm growth
stage between plants fertilized with PSCU and PCU applied with the same method
(Table 5-6). Leaf tissue N concentrations sampled at 20-25 cm growth stage were lower
than in 2007 due to N losses under frequent rainfalls in the early season. Tissue N
concentrations sampled from plants fertilized with (PSCU+AN)2 and PCU were lower
than sufficiency range recommended by UF IFAS. The level of precipitation was 19.3
cm within 30 DAP (days after planting) with an leaching rainfall 8 cm at 29 DAP (Figure
5-1-b), according to leaching rainfall definition by Kidder et al., (1992) for 7.5 cm in 3
days or 10 cm in 7 days. Supplemental application of 34 kg N ha-1 may be needed to
apply at this stage since leaf N tissue concentrations were at the low edge of the
sufficiency (Hutchinson et al., 2002).
Leaf N concentrations were generally lower than sufficiency range at full-flower
stage (Table 5-6). At this stage, there were no significant differences for leaf N
concentrations between plants fertilized with PSCU and PCU applied with the same
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method. At or after full-flower growth stage, the supplemental fertilizers have very low
probability to increase yields (Hochmuth and Cordasco, 2000; Worthington, 2006;
Hutchinson et al., 2009). Without the sufficient N translocated from leaf and stem, tuber
N concentrations were generally lower (1.1% of dry weight basis) averaged over
fertilizer treatments compared to in an averaged tuber N 1.8% of dry weight basis in
2007. This reinforced that the need of additional N due to leaching events to ensure the
optimal yields.
At harvest, with early N loss, there were no significant differences between
fertilizer sources, fertilizer timing and their interaction for tuber TNU and NRE. Tuber
TNU and NRE were also generally lower than in 2007 with an averaged 62.9 kg N ha-1
and 23.0%, respectively. Tuber NRE ranged from 17.3 to 27.4%, with an average of
13% reduction compared to in 2007. These results suggested that CRF with fast
release rate such as PSCU and PCU used in this study may have potential of yield
losses under leaching events.
Soil nutrient analysis
Soil nutrient analysis combined with tissue nutrient analysis would help to provide
more sufficient information for plant N status. The in-season soil NO3-N concentrations
test can also be used to determine whether the supplemental fertilizer N is required for
optimum yields (Belanger et al., 2002; Rodrigues, 2004). The soils with N
concentrations below the critical value will have high probability to respond to
supplemental fertilizer application (Rodrigues, 2004). However, the soil critical value
(CV) may vary over different potato productions, climate patterns, soil fertilizer sources
and application practices (Wilson et al., 2009).
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Both in 2007 and 2008, soil samples taken at pre-fertilization had similar
concentrations of NH4-N and NO3-N (lower than 4.0 mg kg-1 of dry soil basis), indicating
homogenous N levels among experimental plots prior to fertilization. The in season soil
N test had soil N concentrations on hills, higher than in furrow because of in row
banding of fertilizer application. In 2007, soil sampled from plots fertilized with PCU had
greater NO3-N concentrations than PSCU at potato 20-25cm and full-flower growth
stage if both applied with 196 kg N ha-1 preplanting (Table 5-7). This indicated more N
release of PCU with high initial soil temperature if preplanting 196 kg N ha-1 using 100%
PCU than using 100% PSCU. NO3-N concentrations were similar between PSCU and
PCU using the other two application methods. This may be attributed to less percentage
of PSCU or PCU (only 70% of total N) using in the season. Also, the NO3-N
concentrations averaged over fertilizer treatment were 50.3 and 45.6 mg NO3-N kg-1 of
dry soil weight basis at 20-25cm and full-flower growth stage respectively. This NO3-N
level was similar to a predictable level (50 mg kg-1) at 3 weeks after sidedress (around
full-flower stage) for an equivalent N rate with two split application (Munoz, 2004).
Currently, the soil N sufficiency ranges were not recommended by UF/IFAS during the
growing season for Florida potato production due to high variability in weather,
production and soil type. Belanger et al. (2000) suggested a critical value to maximize
tuber yields at 80 mg N kg-1 between 37 to 42 days for north potato production. The
much lower critical values were recommended by Wilson et al. (2009) for 11.3 and 6.0
mg kg-1 at 50 to 55 DAP for soluble and PCU respectively. For Florida, neither NH4-N
nor NO3-N was reported as a clear indicator of tuber yields at harvest in Florida due to
fluctuating conditions (Pack et al., 2004).
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There were similar soil NH4-N and NO3-N concentrations among plots fertilized
with PSCU and PCU applied with the same method. The soil NH4-N and NO3-N
concentrations after harvest was 7.5 and 15.4 mg kg-1 of dry soil basis, respectively,
averaged over fertilizer treatments. The NO3-N concentration average over fertilizer
treatments after harvest was 5 times as the NO3-N concentration prior to fertilization.
This result suggested the importance of cover crops to be planted immediately after
potato crops to avoid subsequent nutrient losses. This reinforced tissue testing of plants
fertilized with CRFs to provide sufficient N in the early stage.
In 2008, soil NH4-N and NO3-N concentrations were similar for soils sampled from
different fertilizer treatments. Both NH4-N and NO3-N concentrations were lower than in
2007 at same growth stage. The low NO3-N concentrations were recorded (below 30
mg kg-1 dry soil weight basis) at 20-25 and full flower growth stages in 2008. The soil
NO3-N concentration after harvest was 18.5 mg NO3-N kg-1 of dry soil basis averaged
over fertilizer treatments.
‘Harley Blackwell’
Tuber production and quality
‘Harley Blackwell’ was released in 2003 by USDA with resistance to IHN, one
major tuber physiological disorder resistance (USDA, Beltsville Md., 2004). ‘Harley
Blackwell’ has the potential as an alternative cultivar for growers for reducing the high
risk of IHN under Florida growing condition of warm soil (Worthington et al., 2006).
The response of ‘Harley Blackwell’ potato plants to fertilizer treatments was
different from ‘Atlantic’ due to different N requirements for each cultivar. In 2007, as
expected, total and marketable yields were generally lower than ‘Atlantic’, with a 5%
and 15% reduction in total and marketable yields averaged over fertilizer treatments,
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respectively. Similar results were reported by (Worthington et al., 2006) for an average
of 8% and 20% reduction for total and marketable yields, respectively as compared to
‘Atlantic’ in study of development of a growing degree day model. In 2007, tuber total
and marketable yields were similar between plants fertilized with PSCU and PCU if
applied with same application timings. Plants fertilized with PSCU produced significantly
lower marketable yields than plants fertilized with PCU if both applied with three split
applications (96, 41 and 59 kg N ha-1 at fumigation, preplanting and hilling,
respectively). This indicated the three split applications of PCU synchronized better with
‘Harley Blackwell’ N demand than PSCU. Plants fertilized with PSCU produced similar
marketable yields than plants fertilized with PCU if both applied preplanting (196 kg N
ha-1) or with two split applications (137 and 59 kg N ha-1 at fumigation and preplanting,
respectively). The similar yield results were attributed to the sufficient N supply by each
treatment with little N loss under relatively dry season in 2007. The N requirements of
‘Harley Blackwell’ in Florida potato production have not been completely studies. Tubers
from plants fertilized with PSCU had similar tuber SG as PCU for all three application
methods, indicating no advantage to use one product over another regarding tuber dry
matter content.
In 2008, ‘Harley Blackwell’ potato total and marketable yields were similar between
plants fertilized with PSCU and PCU applied with the same method. Tuber yields were
generally lower in 2008 than in 2007 due to nutrient losses under frequent rainfalls in
early season (Figure 5-1-b). Tuber size distribution was also similar between plants
fertilized with PSCU and PCU applied with the same method. There was also little
significant difference for tuber external and internal quality. ‘Harley Blackwell’ tubers
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potato plants had a lower IHN incidence (0.3%) over fertilizer treatments than ‘Atlantic’
(3.5%) tubers in 2008. This suggested ‘Harley Blackwell’ was resistant to IHN as
compared to ‘Atlantic’. Similar result was reported by Worthington (2004) that “Harley
Blackwell’ had no IHN while ‘Atlantic’ had 1.7% IHN of total yield.
Tuber SGs were similar between plants fertilized with PSCU and PCU applied with
the same method in 2007 and 2008 with values above 1.078, which was acceptable
according industry chipping standards (USDA, 1991). ‘Harley Blackwell’ tubers are more
resistant to IHN, which is a common internal defect of ‘Atlantic’ grown in Florida due to
high soil temperature during tuber development. This may provide the alternative chip
variety for growers who have greater concerns with risks of internal defects in TCAA.
Similar as ‘Atlantic’, there was similar tuber size distribution or tuber internal and
external quality in 2007 and 2008 between fertilizers with same application timings.
Tissue nutrient analysis
In 2007, leaf N concentrations sampled at 20-25cm stage were above the
sufficiency range (> 6% basis of dry weight) except samples from plants fertilized with
(PSCU+AN)2 had leaf N at 5.9%, also at high edge of sufficiency range (Table 5-11).
This indicated each treatment provided sufficient N for plants in early season including
those with split applications. Leaf tissues sampled from plants fertilized with PSCU had
similar N concentrations as plants fertilized with PCU if both applied preplanting or with
two split applications (137 and 59 kg N ha-1 at fumigation and preplanting, respectively).
Leaf tissues sampled from plants fertilized with (PSCU+AN)2 (96, 41 and 59 kg N ha-1
at fumigation, preplanting and hilling, respectively) had lower N concentrations than
plants fertilized with (PCU+AN)2.
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At full-flower growth stage, leaf tissues sampled from plants fertilized with
(PSCU+AN)2 (96, 41 and 59 kg N ha-1 at fumigation, preplanting and hilling,
respectively) had lower N concentrations than (PCU+AN)2, similar as at 20-25cm
growth stage. This may be attributed to more N release from PCU applied at fumigation
and preplanting than PSCU in 2007 with a high initial soil temperature. Leaf N
concentrations from all treatments were within sufficiency range (3-4% N of dry weight
basis). The leaf tissue N concentration of ‘Harley Blackwell’ plants was 3.6% of dry
weight basis averaged over fertilizer treatments (4.7%), lower than ‘Atlantic’. There were
similar tuber N concentrations with an average 1.5% N of dry weight basis averaged
among fertilizer treatments. There were no significant differences for vine (leaf+stem)
TNU or tuber TNU between plants fertilized with PSCU and PCU applied with the same
method, with an range from 45.1 to 61.2 kg ha-1and from 33.3 to 80.4 kg ha-1 for vine
(leaf+stem) and tuber respectively. ‘Harley Blackwell’ plants recovered lower amount of
N in vine at full-flower stage due to a lower N concentration in leaf tissue as compared
to ‘Atlantic’ plants. This may also be partially attributed to lower yields of ‘Harley
Blackwell’ because of less supply of N from vine at tuber development.
At harvest, there were no significant differences between plants fertilized with
PSCU and PCU applied with the same method for tuber total N removal (TNR) and
NRE, ranging from 85.0 to 100.6 kg ha-1 and from 30.2 to 37.3%. Similar as ‘Atlantic’,
the accumulate N in vine at full-flower stage was translocated to tubers during tuber
development period.
In 2008, similar as ‘Atlantic’, leaf tissue N concentrations were generally low at 20-
25 cm growth stage with an average of 3.3 % N dry weight soil basis, which was a 50%
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reduction from 2007. Similar as in 2007, leaf tissues sampled from plants fertilized with
(PSCU+AN)2 (96, 41 and 59 kg N ha-1 at fumigation, preplanting and hilling,
respectively) had lower N concentrations than (PCU+AN)2. This reinforced more N was
released from PCU applied at fumigation and preplanting than PSCU with a late
planting season.
At full-flower stage, there were similar leaf, stem N concentrations and TNUs in
vine (leaf+stem) between plants fertilized with PSCU and PCU applied with the same
method. At harvest, there were no significant differences between fertilizers applied with
same application timings for tuber total N removal (TNR) and NRE, ranging from 53.4 to
71.5 kg ha-1 and from 17.3 to 27.4%.
Soil nutrient analysis
In 2007, there were no significant differences for soil NH4-N at potato 20-25 cm
stage between PSCU and PCU if applied in same methods (Table 5-13). However, at
20-25 cm growth stage, soil sampled from plots fertilized with PCU had greater NO3-N
concentrations than PSCU if applied preplanting or with three split applications (Table 5-
13). This may be attributed to difference release characteristic between PSCU and
PCU. N release of PCU was promoted by relatively high soil temperature in 2007 with a
late planting. At this growth stage, soil NO3-N concentrations averaged over fertilizer
treatment were 63.2 mg kg-1, which was greater than soils with ‘Atlantic’ plants. This
suggested the lower N uptake prior to 20-25cm growth stage by ‘Harley Blackwell’ than
‘Atlantic’, which also resulted in lower leaf N concentrations for ‘Harley Blackwell’.
At full-flower growth stage, there were similar soil NO3-N concentrations at full-
flower growth stage between PSCU and PCU with same application method with the
average 11.9 and 43.2 mg kg-1, respectively. This was similar to average tissue N
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concentration of ‘Atlantic’ plants, which were 11.7 and 45.6 kg ha-1 for NH4-N and NO3 –
N respectively. At harvest, similar as ‘Atlantic’, there were no significant difference for
soil NH4-N and NO3-N concentrations with an average at 7.8 and 18.1 mg kg-1,
respectively. This also suggested a lower N uptake by ‘Harley Blackwell’ during a
growing season compared to ‘Atlantic’.
In 2008, similar as ‘Atlantic’, soil NH4-N and NO3-N concentrations were lower at
20-25 cm and full-flower growth stage than in 2007 due to the early N loss under
rainfall. Soil NH4-N concentrations were similar between PSCU and PCU at 20-25 cm
growth stage if applied in same way with an average 2.9 mg kg-1 soil dry weight basis.
Same as ‘Atlantic’, at this growth stage soil sampled from plots fertilized with PCU had
greater NO3-N concentrations than PSCU if both applied preplanting. At full-flower grow
stage, there were minimal significant differences for NH4-N and NO3-N concentrations
between PSCU and PCU if applied in same method. The soil NO3-N concentration after
harvest was 21.9 mg NO3-N kg-1 of dry soil basis averaged over fertilizer treatments,
higher than ‘Atlantic’. This reinforced a less N uptake by ‘Harley Blackwell’ during a
growing season compared to ‘Atlantic’.
‘FL2053’
Tuber yields and quality
Though ‘FL 2053’ is not commercially grown in Florida, the potentials of this
cultivar have been evaluated under Florida growth conditions as alternative potato
cultivar for TCAA potato growers. The yield response of ‘FL 2053’ potato plants to the
fertilizer treatment was similar to ‘Atlantic’.
In 2007, total and marketable yields of ‘FL 2053’ average over fertilizer treatments
were 3% and 5% lower than ‘Atlantic’, respectively. ‘FL 2053’ total and marketable
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yields were similar between plants fertilized with PSCU and PCU if applied in same
method. There was no significant difference regarding yield performance between
PSCU and PCU for either application method. This indicated the flexible fertilizer source
and application timing for ‘FL 2053’. There were similar tuber SGs between plants
fertilized with PSCU and PCU if applied in same method. Tuber SGs were similar for
plants fertilized with different fertilizer sources or timings with average value at 1.079,
same as the averaged SG for ‘Atlantic’ potatoes at University of Florida Hasting
research farm (Hutchinson et al., 2002). There was minimal significant difference for
tuber external or internal quality between fertilizer treatments. However, the ‘FL2053’
had greater percentage of ‘growth crack’ (2.5%), a physiological disorder than ‘Atlantic’
(0.2%) in 2007 with the warm growing season. The difference would be attributed to
susceptible difference among cultivars. Although no literature is available of the
susceptibility of ‘FL 2053’ to ‘growth crack’, ‘FL 2053’plants can have high incidence of
growth crack defects under certain stressful growing conditions (Personal
communication with Frito-Lay). Different from ‘Atlantic’, ‘FL 2053’ under the stressful
growing in 2008 had low tuber internal defects with no IHN observed in each treatment.
In 2008, similar as ‘Atlantic’, there were no significant differences for total and
marketable yields between plants fertilized with PSCU and PCU if applied in same
method. Tuber yields were also generally lower in 2008 than in 2007 due to nutrient
losses under frequent rainfalls in early season (Figure 5-1-b). Tubers SGs were greater
for plants fertilized PCU (1.084) than plants fertilized with PSCU if both applied
preplanting. There was minimal significant difference for tuber external or internal
quality between fertilizer treatments.
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These results suggested that ‘FL2053’ can also be considered as an alternative
chipping variety for TCAA potato growers with greater internal quality. The PSCU and
PCU application for ‘FL 2053’ were more flexible for application timing.
Tissue nutrient analysis
In 2007, leaf N concentrations were above sufficiency range (above 6% dry weight
basis) at 20-25 cm growth stage except plants fertilized with (PSCU+AN)2. This
indicated that each fertilizer treatment also provided sufficient N in early season for ‘FL
2053’ as same as for ‘Atlantic’. Similar as ‘Atlantic’ and ‘Harley Blackwell’, at potato 20-
25 cm growth stage, leaf tissues sampled from plants fertilized with (PSCU+AN)2 had
significantly lower N concentrations than plants fertilized with (PCU+AN)2. At full-flower
growth stage, leaf tissue N at full-flower growth stage were within sufficient range (3-
4%), indicating no deficiency of N by any fertilizer treatment at this growth stage. Leaf
tissues sampled from plants fertilized with PSCU had similar N concentration as plants
fertilized with PCU for all application methods.
At harvest, there were no significant differences for tuber TNR and NRE between
plants fertilized with PSCU and PCU if applied in same method. TNRs and NREs from
plants were 100.8 kg N ha-1 and 39.1% averaged over fertilizer treatments, respectively.
In 2008, similar as ‘Atlantic’, the great reduction in tissue N was found for leaf,
stem and tuber at both 20-25 cm and full-flower growth stages with greater 50%
reduction of 2007. The leaf tissue N concentrations at these two critical stages were
both below N sufficiency range, resulting in yield losses. There were similar leaf, stem,
tuber N concentrations between plants fertilized with PSCU and PCU if applied in same
method. There were also no significant differences for TNUs in vine (leaf+stem)
between plants fertilized with PSCU and PCU if applied in same method.
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At harvest, with the yield reduction and low tuber N concentrations, tuber TNRs
and were similar among fertilizer treatments with the average 76.5 kg ha-1 and 30.1%,
respectively.
Soil nutrient analysis
In 2007, NO3-N concentrations were higher for soils fertilized with PCU treatments
at 20-25 cm and full-flower growth stage than PSCU if applied preplanting or with three
split applications (Table 5-18). NH4-N and NO3-N concentration at full-flower growth
stage and harvest were 12.7 and 34.3, 9.6 and 17.6 mg kg-1 soil dry weight basis,
respectively.
In 2008, soil NH4-N and NO3-N concentrations were low at 20-25 cm and full-
flower growth stage due to the early N loss under rainfall. Soil NH4-N and NO3-N
concentrations were similar between PSCU and PCU at 20-25 cm growth stage if
applied in same method with an average 2.9 and 17.6 mg kg-1 soil dry weight basis. At
full-flower growth stage, samples from soils fertilized with PCU 100% N preplanting had
greater NO3-N concentrations. Soils NH4-N and NO3-N at harvest stage were similar
between fertilizer treatments with average 2.8 and 17.8 mg kg-1 soil dry weight basis,
respectively.
Perched Water Table Quality
The perched table water samplings (only for ‘Atlantic’) were conducted biweekly
after the last fertilizer applications (sizedress of AN at hilling) in each growing season.
The monitoring perched water NH4-N and NO3-N concentrations during growing season
can help to determine if there were any differences among fertilizer treatments.
In both 2007 and 2008, there were no significant differences for NH4-N or NO3-N
concentration between plants fertilized with PSCU and PCU if applied in same method
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at each sampling date, indicating no advantage of one fertilization practice over another
with respect to ground water quality. This may also be attributed to no significant rainfall
after the last fertilization in 2007 (sizedress of AN) while potential of early N prior to first
sampling date in 2008. Therefore, water sample NH4-N and NO3-N concentrations
averaged over fertilizer treatments were used to show the trend of N concentration
change during growing season (Figure 5-2). In 2007, both NH4-N and NO3-N
concentrations were decreasing when growing season proceeded with highest NO3-N
concentration (2.9 mg L-1) averaged over fertilizer treatments at 8 days after last
fertilization, lower than the maximum contaminant level 10 m L-1 (USEPA, 2003). Similar
trends were also reported in Florida seepage-irrigated potato (Pack et al., 2006; Munoz
et al., 2008). There was minimal N leaching in the late season due to a dry season in
2007. There may be early N leaching in the perched water table. However, the early
observations of perched ground water were not available in this study due to insufficient
samplings.
In 2008, because of the potential N losses in early season prior to the last
fertilization, water sample NH4-N and NO3-N were generally lower with approximate 0.7
mg L-1 NO3-N concentration during the late season. The leaching rainfall may also dilute
the leaching N with high amount water loading into perched water table, resulting in low
NO3-N (Pack et al., 2006). Therefore, the early season perched ground water samplings
are important to monitor N losses as well as sampling immediately after rainfalls. The
alternative method of well installation need to be consider without conflict with other
agricultural practices.
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Overall, this research demonstrated that the potential of PSCU and PCU at 196 kg
N ha-1 with flexible application timing to synchronize plant N demand for Florida
‘Atlantic’ potato production. PSCU and PCU provided sufficient N in early season for
‘Atlantic’ plants, resulting in minimal benefits from sidedress AN at hilling. Plants
fertilized with PSCU produced greater yields than PCU if applied with two split
applications (96 and 41 kg N ha-1 at fumigation and preplanting) combined with AN (59
kg N ha-1) at hilling. The additional N applications are also necessary for optimal yields
for PSCU or PCU applications if leaching events occurs.
‘Harley Blackwell’ plants fertilized with PCU produced greater yields than PSCU if
applied with two split applications (96 and 41 kg N ha-1 at fumigation and preplanting)
combined with AN (59 kg N ha-1) at hilling. This suggested the possibility of higher N
demand of ‘Harley Blackwell’ in early season than ‘Atlantic’. ‘FL2053’ had the similar
yield response to fertilization as “Atlantic’ when grown in Florida potato production,
indicating more flexibility of this cultivar for fertilization management. Though with lower
yields, ‘Harley Blackwell’ and ‘FL 2053’ had resistance to IHN as compared with
‘Atlantic’. These two cultivars may provide the alternative chipping cultivars for Florida
potato growers.
Plants fertilized with PCU had significantly greater leaf N concentrations at 20-
25cm growth stage than plants fertilized with PSCU because of different release
characteristics. The leaf tissue testing over current UF/IFAS nutrient sufficiency range
may not result from over application. Further research should investigate for accurate
sufficiency range associated different growth stages and determine the critical values
for optimum yields. However, leaf tissue testing N under sufficiency range should trigger
121
an immediately supplemental N application following UF/IFAS recommendation with in
row application to avoid yield reduction.
122
Table 5-1. Fertilizer formulation, manufacturer, nitrogen form, and water solubility. Type Formulationz Manufacturer N formy Characteristics 1 34-0-0 Gator Fertilizer AN Water soluble 2 44-0-0 Agrium Fertilizers PCU Water insoluble 3 38-0-0 Scotts Chemical Co. PSCU Water insoluble
zPecent N-P2O5-K2O yAN: ammonium nitrate; PSCU: polymer sulfur coated urea; PCU: polymer coated urea.
Table 5-2. Fertilizer treatments for potatoes grown under traditional and alternative fertilizer programs from Hastings, FL in 2007, 2008 and 2009.
N rate in application timingz (kg ha-1) Treatment Fertilizerx
N rate (kg ha-1) Fumigation Preplanting Hilling
1 PSCU 196 0 196 0 2 (PSCU+AN)1 196 137 (PSCU) 59 (AN) 0 3 (PSCU+AN)2 196 96 (PSCU) 41 (PSCU) 59 (AN) 4 PCU 196 0 196 0 5 (PCU+AN)1 196 137 (PCU) 59 (AN) 0 6 (PCU+AN)2 196 96 (PCU) 41 (PCU) 59 (AN) z Fumigation, preplanting and hilling timings were around 21 days, 1 day prior to planting, and 10 days after emergence, respectively in each growing season yAN, PSCU, and PCU represent ammonium nitrate, polymer sulfur-coated urea and polymer coated urea, respectively
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Table 5-3. Influence of fertilizer source and timing of application on ‘Atlantic’ tuber yield and specific gravity when grown in Hastings, FL during 2007.
Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 36.0 31.1 1.082
(PSCU+AN)1 38.2 32.8 1.085
(PSCU+AN)2 33.6 27.9 1.083 PCU 33.4 27.6 1.081
(PCU+AN)1 33.1 27.2 1.082
(PCU+AN)2 35.7 30.3 1.083 Contrastw
PSCU vs PCU NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 * ** NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively. Table 5-4. Influence of fertilizer source and timing of application on ‘Atlantic’
tuber yield and specific gravity when grown in Hastings, FL during 2008.
Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 23.2 18.9 1.082
(PSCU+AN)1 24.2 19.0 1.080
(PSCU+AN)2 24.5 18.9 1.079 PCU 23.8 19.6 1.085
(PCU+AN)1 24.1 19.4 1.085
(PCU+AN)2 24.0 19.5 1.082 Contrastw
PSCU vs PCU NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS **
(PSCU+AN)2 vs (PCU+AN)2 NS NS * zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively.
124
Table 5-5. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Atlantic’ potatoes from Hastings, FL during 2007.
20-25cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 6.6 4.8 56.9 28.2 105.5 53.8
(PSCU+AN)1 6.6 4.6 89.7 62.4 111.6 56.9
(PSCU+AN)2 5.7 4.5 66.2 49.7 83.6 42.6 PCU 6.8 5.7 83.3 38.4 91.5 46.7
(PCU+AN)1 6.8 3.5 56.9 37.8 80.2 40.9
(PCU+AN)2 6.3 5.1 91.1 31.7 103.4 52.8 Contrastx
PSCU vs PCU NS NS NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 ** NS NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS Nonsignficant (NS).
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Table 5-6. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Atlantic’ potatoes from Hastings, FL during 2008.
20-25cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 3.1 1.0 20.6 25.0 56.1 19.6
(PSCU+AN)1 3.2 1.9 23.0 19.3 53.4 18.2
(PSCU+AN)2 2.6 1.4 19.6 14.4 71.5 27.4 PCU 2.7 1.9 14.7 20.3 68.1 25.7
(PCU+AN)1 3.4 1.9 24.0 15.0 62.4 22.8
(PCU+AN)2 4.4 1.3 17.2 18.5 65.8 24.5 Contrastx
PSCU vs PCU NS NS NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively.
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Table 5-7. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘Atlantic’ potato grown with different fertilizer treatments from Hastings, FL during 2007.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N ---------------------------mg kg-1--------------------------PSCU 7.0 6.8 51.1 26.7 (PSCU+AN)1 7.0 7.9 50.6 46.5 (PSCU+AN)2 8.5 20.9 47.4 44.1 PCU 9.3 27 37.1 58.5 (PCU+AN)1 4.7 7.8 55.6 53.4 (PCU+AN)2 5.5 7.1 60.2 44.5 Contrasty
PSCU vs PCU * ** ** ** (PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS (PSCU+AN)2 vs (PCU+AN)2 NS NS NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively. Table 5-8. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight
basis) for ‘Atlantic’ potato grown with different fertilizer treatments from Hastings, FL during 2008.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N ---------------------------mg kg-1--------------------------PSCU 6.6 1.0 17.7 19.2 (PSCU+AN)1 1.3 0.7 11.7 5.3 (PSCU+AN)2 3.9 1.7 21.8 22.2 PCU 4.2 0.9 27.5 27.4 (PCU+AN)1 1.0 0.7 13.5 14.6 (PCU+AN)2 2.5 1.6 22.4 17.1 Contrasty
PSCU vs PCU NS * NS NS (PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS (PSCU+AN)2 vs (PCU+AN)2 NS NS NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, * Nonsignficant (NS) or significant at P ≤ 0.05.
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Table 5-9. Influence of fertilizer source and timing of application on ‘Harley Blackwell’ tuber yield and specific gravity when grown in Hastings, FL during 2007.
Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 35.7 28.3 1.079
(PSCU+AN)1 34.5 25.6 1.082
(PSCU+AN)2 29.6 21.7 1.082 PCU 31.9 24.7 1.079
(PCU+AN)1 33.4 24.3 1.081
(PCU+AN)2 34.1 26.8 1.081 Contrastw
PSCU vs PCU * NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 ** ** NS zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively. Table 5-10. Influence of fertilizer source and timing of application on ‘Harley
Blackwell’ tuber yield and specific gravity when grown in Hastings, FL during 2008.
Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 23.5 17.9 1.080
(PSCU+AN)1 18.6 13.2 1.078
(PSCU+AN)2 18.4 13.5 1.076 PCU 20.5 16.0 1.079
(PCU+AN)1 22.1 16.0 1.081
(PCU+AN)2 22.1 15.8 1.079 Contrastw
PSCU vs PCU NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS Nonsignficant (NS).
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Table 5-11. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Harley Blackwell’ potatoes from Hastings, FL during 2007.
20-25 cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 6.7 3.7 47.5 36.9 99.0 37.3
(PSCU+AN)1 6.7 3.7 48.0 35.8 94.8 35.1
(PSCU+AN)2 5.9 3.3 45.1 50.8 85.0 30.2 PCU 7.0 4.1 57.3 33.3 97.4 36.5
(PCU+AN)1 6.7 3.8 61.8 47.7 93.1 34.3
(PCU+AN)2 6.4 3.8 49.0 80.4 89.6 32.5 Contrastx
PSCU vs PCU NS * NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 * * NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS, * Nonsignficant (NS) or significant at P ≤ 0.05.
129
Table 5-12. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘Harley Blackwell’ potatoes from Hastings, FL during 2008.
20-25 cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 2.6 1.3 34.8 13.0 60.2 30.7
(PSCU+AN)1 2.9 1.5 22.1 12.2 41.8 21.3
(PSCU+AN)2 2.8 1.4 23.5 17.1 49.2 25.1 PCU 3.1 1.2 13.2 26.6 55.1 28.1
(PCU+AN)1 3.9 1.2 19.1 19.9 48.8 24.9
(PCU+AN)2 4.7 1.7 30.4 14.6 49.0 25.0 Contrastx
PSCU vs PCU NS NS NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 * NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 ** NS NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively.
130
Table 5-13. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25cm and full-flower growth stage for ‘Harley Blackwell’ potato grown with different fertilizer treatments from Hastings during 2007.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N PSCU 12.1 70.9 10.1 21.9 (PSCU+AN)1 2.5 60.2 5.3 39.9 (PSCU+AN)2 1.8 34.4 16.8 44.3 PCU 16.0 101.2 19.0 53.4 (PCU+AN)1 2.2 45.4 12.0 51.9 (PCU+AN)2 2.8 67.1 8.3 47.5 Contrasty
PSCU vs PCU NS * NS NS (PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS (PSCU+AN)2 vs (PCU+AN)2 NS * NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, * Nonsignficant (NS) or significant at P ≤ 0.05. Table 5-14. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at
potato 20-25cm and full-flower growth stage for ‘Harley Blackwell’ potato grown with different fertilizer treatments from Hastings during 2008.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N PSCU 3.7 10.8 4.0 36.5 (PSCU+AN)1 1.8 8.3 1.4 14.8 (PSCU+AN)2 5.5 25.4 2.4 21.0 PCU 2.8 29.0 0.9 50.3 (PCU+AN)1 1.1 13.7 0.8 15.3 (PCU+AN)2 8.0 29.7 0.8 18.7 Contrasty
PSCU vs PCU NS * * NS (PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS (PSCU+AN)2 vs (PCU+AN)2 NS NS NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, * Nonsignficant (NS) or significant at P ≤ 0.05.
131
Table 5-15. Influence of fertilizer source and timing of application on ‘FL 2053’ tuber yield and specific gravity when grown in Hastings, FL during 2007.
Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 34.0 28.5 1.078
(PSCU+AN)1 35.5 29.0 1.080
(PSCU+AN)2 32.9 26.2 1.081 PCU 31.3 26.0 1.079
(PCU+AN)1 34.7 27.9 1.079
(PCU+AN)2 35.6 30.7 1.079 Contrastw
PSCU vs PCU NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS Nonsignficant (NS). Table 5-16. Influence of fertilizer source and timing of application on ‘FL 2053’ tuber
yield and specific gravity when grown in Hastings, FL during 2008. Total yield Marketable yieldz SGy
Treatmentsx ------------T ha-1-----------
PSCU 25.0 17.6 1.081
(PSCU+AN)1 23.2 16.9 1.079
(PSCU+AN)2 23.7 16.6 1.078 PCU 25.2 19.0 1.084
(PCU+AN)1 25.5 17.1 1.082
(PCU+AN)2 24.6 17.1 1.080 Contrastw
PSCU vs PCU NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS zMarketable yield: 10.2 cm ≥ tuber size classes ≥ 4.4 cm. ySG=specific gravity. xSee Table 5-2 for fertilizer rate and timing of application. wNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively.
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Table 5-17. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25 cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘FL 2053’ potatoes from Hastings, FL during 2007.
20-25 cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 6.6 4.0 46.1 53.3 103.0 39.0
(PSCU+AN)1 6.7 4.2 51.5 34.5 98.6 44.2
(PSCU+AN)2 5.8 4.0 54.9 58.5 98.6 37.0 PCU 6.9 3.8 52.4 38.9 97.4 35.9
(PCU+AN)1 6.9 4.0 54.4 33.3 106.4 40.3
(PCU+AN)2 6.4 3.2 39.7 33.9 100.8 38.1 Contrastx
PSCU vs PCU NS NS NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 ** NS NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS, ** Nonsignficant (NS) or significant at P ≤ 0.01.
133
Table 5-18. Nitrogen concentration and removal by plant tissue type on per-hectare basis at 20-25 cm and full-flower growth stage and tuber N recovery efficiency (NRE) at harvest for ‘FL 2053’ potatoes from Hastings, FL during 2008.
20-25 cm Full-flower Harvest
Treatmentsy Leaf (%z) Leaf (%) Vine (kg ha-1) Tuber (kg ha-1) Tuber (kg ha-1) NRE (%) PSCU 2.9 1.5 23.5 15.5 70.1 26.9
(PSCU+AN)1 2.8 1.7 20.1 17.4 62.2 22.8
(PSCU+AN)2 3.0 1.2 18.1 14.8 63.4 23.4 PCU 3.4 1.3 23.0 32.7 92.9 38.5
(PCU+AN)1 3.1 1.1 16.7 19.8 78.0 30.9
(PCU+AN)2 3.5 1.5 25.5 15.2 92.3 38.2 Constrastx
PSCU vs PCU NS NS NS NS NS NS
(PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS NS NS
(PSCU+AN)2 vs (PCU+AN)2 NS NS NS NS NS NS zAll % values are on a dry weight basis. ySee Table 5-2 for fertilizer rate and timing of application. xNS Nonsignficant (NS).
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Table 5-19. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at potato 20-25 cm and full-flower growth stage for ‘FL 2053’ potato grown with different fertilizer treatments from Hastings, FL during 2007.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N PSCU 3.2 57.6 7.3 23.1 (PSCU+AN)1 1.5 57.0 8.1 39.0 (PSCU+AN)2 3.2 41.1 10.7 63.9 PCU 15.2 97.0 29.3 50.0 (PCU+AN)1 1.9 63.6 11.5 46.9 (PCU+AN)2 2.3 72.7 9.5 27.9 Contrasty
PSCU vs PCU * * ** * (PSCU+AN)1 vs (PCU+AN)1 NS NS NS NS (PSCU+AN)2 vs (PCU+AN)2 NS * NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively. Table 5-20. Nitrogen concentrations of soil samples (mg N kg-1 dry soil weight basis) at
potato 20-25cm and full-flower growth stage for ‘FL 2053’ potato grown with different fertilizer treatments from Hastings, FL during 2007.
20-25cm Full-flower
Treatmentsz NH4-N NO3-N NH4-N NO3-N PSCU 2.6 13.8 1.0 14.4 (PSCU+AN)1 2.2 9.2 2.1 14.6 (PSCU+AN)2 5.5 27.0 0.9 10.9 PCU 2.6 17.9 1.6 26.0 (PCU+AN)1 2.4 16.5 0.7 9.6 (PCU+AN)2 2.1 21.0 0.8 9.6 Contrasty
PSCU vs PCU NS NS NS * (PSCU+AN)1 vs (PCU+AN)1 NS NS ** NS (PSCU+AN)2 vs (PCU+AN)2 * NS NS NS
zSee Table 5-2 for fertilizer rate and timing of application. yNS, *, ** Nonsignficant (NS) or significant at P ≤ 0.05 or 0.01, respectively.
135
A
B
Figure 5-1. Average daily temperature (60cm air temperature and 10 cm soil temperature) and daily rainfall (cm) during growing seasons (from planting to harvest). A) 2007. B) 2008.
136
A
B
Figure 5-2. NH4-N and NO3-N concentrations in the perched ground water after the last fertilization averaged over fertilizer treatment. A) 2007. B) 2008.
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CHAPTER 6 CHARACTERIZATION OF IN-ROW MOVEMENT OF NITROGEN DURING A RAIN
EVENT AND ITS IMPACT ON NORTHEAST FLORIDA SEEPAGE IRRIGATED POTATO PRODUCTION
Introduction
Potato is considered as one of most important edible horticultural crops in Florida
with about 117,200 hectares grown in 2008-2009 production season (USDA, 2009).
Approximately 60% of Florida potato production is in the tri-county agricultural area
(TCAA), (Flagler, Putnam and St. Johns counties) (USDA, 2009).
Potato plants generally require high N input for optimum yields which increases
potential for nitrate losses (Munoz et al., 2008). Growers tended to apply more N than
the plant demand (Zotarelli et al., 2007). Seepage irrigation system and sandy soils in
the potato production of the TCAA also promote nutrient losses due to the continuous
open bed irrigated throughout the season. Leaching of NO3-N in agricultural area in
Florida may result in contamination of surrounding surface or ground water. The
maximum contaminant level of drinking water for NO3-N is 10 mg L-1 (USEPA, 2003).
The NO3-N concentrations in surface water near the Florida agricultural production area
have been reported to exceed the maximum contaminant level 49% of the time
(Wicklein, 2004). The NO3-N concentrations over 10 mg L-1 have also been reported for
surface water surrounding potato production in Minnesota area, USA and Quebec,
Canada (Gallus and Montgomery, 1998; Madramootoo et al., 1992). Best Management
Practices (BMPs) are under development to assist growers to maintain or increase
economical yields while reducing nutrient loads to water bodies. The main objection of
BMP implementation in the TCAA is to reduce NO3-N movement from potato production
areas to the St John River basin.
138
Many studies have been accomplished to evaluate alternative cultural practices to
improve N use efficiency and minimize leaching potential, such as N rates, placement,
and timing (Errebhi et al., 1998, Waddell et al., 1999, Whitley and Davenport, 2003.,
Delgado et al., 2005). In Florida, the BMP N rate for potatoes has been established at
224 kg N ha-1 with possibility to apply additional 34 kg N ha-1 under leaching events
(Hochmuth and Hanlon, 2000; Livingston-Way, 2000). Leaching events are defined as
7.6 cm in 3 days or 10.0 cm in 7 days (Kidder et al., 1992). However, synchronizing
fertilizer application to match crop nutrient demand while reducing nutrient losses
remains a major challenge in crop management (Tilman et al., 2002). In the TCAA, the
supplemental fertilizers are commonly surface applied granular N fertilizer with soil
covered by hilling to avoid root damage. This application method may not provide a
rapid plant response since inorganic fertilizers are surfaced applied where few potato
roots are located (Worthingston et al., 2007; Munoz et al., 2008). Also, additional
fertilizer applications may be limited in the TCAA when canopy of potato crops are well
development.
Controlled release fertilizers (CRFs) formulated to synchronize plant N demand is
another alternative to maximize N use efficiency and minimize leaching. Zvomuya et al.
(2003) reported that at N rate of 280 kg N ha-1, NO3-N leaching was 34 to 49% lower
with polymer coated urea (PCU) treatments than three split applications of urea while N
recovery efficiency (NRE) for PCU averaged 50%, 7% higher than three split
applications of urea (NRE averaged 43%). The plants fertilized with CRFs produced
comparable yields for ‘Atlantic’ potato in Florida as ammonium nitrate (AN) but with
significantly lower NO3-N concentration at root zone level (30 cm) at early season than
139
AN (Pack et al., 2006). Therefore, potato plants fertilized with CRFs at 196 kg N ha-1
have been reported to produce comparable yield and quality to plants fertilized with
soluble N at 224 kg N ha-1 due to its higher N use efficiency (Hutchinson, 2005,
Worthington et al., 2007).
However, the effect of CRFs on in-row N leaching is not clearly evaluated under
potato system in Florida. The timing and intensity of rainfall are also important as
minimal N is required when potato plants is establishing, which increases the potential
of N losses in early season (Errebhi et al., 1998). Also, manufacturers formulate
various CRFs using different materials and release mechanisms without providing
sufficient information about their release characteristics. CRFs may differ in their
susceptibility to nutrient leaching because of their different nutrient release rate.
Therefore, it is important to evaluate the influence of CRF source on potato production
and in-row nutrient leaching.
This study was conducted to 1) quantify N concentration and load of leachate into
perched water table under 5 cm rainfall at two critical potato growth stages; 2) evaluate
the efficacy of CRFs in reducing nutrient leaching and influence on potato tuber yields
and quality and; 3) compare the influence of different CRFs on tuber production, quality
and in reducing in-row N leaching into water table under 5 cm rainfall.
Materials and Methods
Site Description
The experiment was conducted at the University of Florida’s Partnership for Water,
Agriculture, and Community Sustainability at Hastings farm in 2008. Soil was Ellzey fine
sand, classified as a sandy, siliceous, hyperthermic Arenic Ochraqualf (sand 90% to
95%, <2.5% clay, <5% silt) (USDA, 1983). Potato cultivar ‘Atlantic’ was used. Seepage
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irrigation was used to maintain a perched water table at 45-60 cm below the surface of
the potato row. Weather data (rainfall, temperatures) were recorded for the growth
season through the Florida Automated Weather Network (FAWN, 2008).
Experimental Design
The experiment design was a randomized completed block design with treatments
replicated four times. Plots were four rows wide (100 cm between rows) by 610 cm long.
Within-row spacing was 20 cm. Potato seed pieces were planted on 27 Feb. and
harvested on 9 Jun. 2008.
Four CRFs polymer sulfur coated urea (PSCU 380 g N kg-1, Scott Chemical Co.
Maryville, OH), polymer coated urea (PCU 440 g N kg-1, Agrium INC, ), two liquid urea
formaldehyde (UF) products (UF1 300 g N kg-1, Georgia Pacific Chemicals LLC), and
(UF2 280 g N kg-1, Helena Chemical Co.) were applied at 196 kg N ha-1. All fertilizer
programs were banded with in row application 1 day prior to planting. Each plot
received 15 kg P ha-1 and 163 kg K ha-1 at planting based on soil test results
(Hutchinson et al., 2009). Plots were irrigated with seepage irrigation during the
growing season except during leaching events (7.6 cm in 3 days or 10.0 cm in 7 days)
and receive of sufficient rainfall. Natural and simulated leaching rainfall received in each
plot at the 20-25 cm growth stage (35-45 DAP) and at full-flower (55-65 DAP) growth
stage, respectively. Natural rainfall was a 5 cm rainfall in a 2 day period at potato 20-25
cm growth stage while the simulated leaching event was applied with 5 cm artificial
rainfall via overhead solid set sprinkle irrigation system (#4 mini-wobblers; 30 psi;
Senninger Irrigation, INC., Clermont, FL) in two hours. Four rain gauges were randomly
set in plots to monitor irrigation quantities. Data were only collected from the two central
rows of each plot.
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Drainage Lysimeter Installation and Water Sampling
The drainage lysimeter was designed to assess the in row water movement into
the perched water table (45-60 cm below row during the growing season). Each
drainage lysimeter was composed of a PVC cup with radius 15.4cm, a drainage plate,
and a 255 microns nylon screen (Figure 6-2-a). The nylon screen was sufficiently fine to
be glue at surface of the drainage plate to hold the soil while allowing water to penetrate
into the PVC cup, which acted as a collection chamber. A collection tube penetrated
from the middle of drainage plate to the bottom of PVC cup for leachate water
collection. A drainage lysimeter was installed in each plot at a 45 cm depth from the
surface of the row to monitor N leaching passing into the perched water table.
The collection chamber of the drainage lysimeter was emptied of water by a
handmade suction device before the 5 cm natural and simulated rainfall at the 20-25cm
and full-flower growth stages. The leachate was collected 24 hours after the 5 cm
rainfall through a soft nylon hose sticking in the collected tuber into the bottom of
drainage lysimeter to a vacuum created inside a 3000 ml beaker by a pneumatic pump.
The volume of leachate sample from each plot was recorded and a sub-water sample
was collected in a 20 mL high-density polyethylene vial. The sub water samples were
filtered, acidified, and frozen until they were analyzed at the UF/IFAS analytical
Research Laboratory (ARL) for nitrate (NO3-N), ammonium (NH4-N), total Kjeldahl
nitrogen (TKN) concentration ((Mylavarapu and Kennelley, 2002). Since drainage
lysimeters catch the entire leachate volume passing below a specific soil depth, nutrient
leaching into perched water table was calculated according to the following formula
(Zotarelli et al., 2007):
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Nutrient leaching= (nutrient concentration × leachate volume)/(drainage
surface/hectare surface).
The leaching was converted into the per hectare basis. NH4-N and NO3-N loads into
perched water table were calculated separately. Since TKN values measured the sum
of organic N, NH3 and NH4-N, total N loads were calculated as the sum of NO3-N and
TKN loads.
Soil Sampling
Soil samples were collected after irrigation from each plot. At each sampling time,
a composite sample (eight cores) was taken using soil probe from each plot at a 15 cm
depth. The collected soil samples were air-dried, sieved to remove the debris and were
analyzed for NO3-N, NH4-N, total Kjeldahl N (TKN), P and K at the University of
Florida’s Analytical Research Laboratory (ARL). Soil moisture was measured at 10, 20,
30, 40, 60, and 100 cm below the soil surface with a soil moisture probe (Dynamax
PR2/6 profile, Dynamax INC, Houston, TX) before and after the 5 cm rainfall events.
Tuber Yield and Quality
The center two rows of each plot were mechanically harvested with a one row
commercial harvester (Middleton Harvester 40, Middleton Harvester Inc, Elkton, FL).
Potato tubers were washed and graded into six size classes using a commercial
grading machine according to USDA grading standards (USDA, 1991). The marketable
yield was defined as the weight of U.S. No. 1 tubers with diameters between 4.4 and
10.2 cm without external defects (USDA, 1991). Specific gravity (SG) was determined
using the weight in air/weight in water method (Edgar, 1951).
A subsample of randomly selected marketable tubers (20) was collected after
grading table for each plot. Each tuber was cut into quarters and rated for incidence of
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internal defects including disease and physiological disorders. The disease included
corky ring spot (CRS) and brown spot (BR) and physiological disorders included hollow
heart (HH), internal heat necrosis (IHN) and brown center (BC). All tuber internal
defects were reported as incidence in percentage of total yield.
Statistical Analysis
Data were analyzed within each year due to the variable environmental conditions
such as soil temperature, rainfall during season etc. All data were subjected to analysis
of variance (ANOVA) using SAS ANOVA to evaluate main and interaction effects (SAS
Institute, 2004). Treatment means were separated using Duncan’s multiple range test at
ρ ≤ 0.05.
Results and Discussion
Tuber Production and Quality
In 2008, fertilizer program had significant influence on ‘Atlantic’ tuber total and
marketable yields with the natural and simulated 5 cm rainfalls that occurred at potato
20-25 cm and full-flower growth stages (Table 6-2). Without supplemental N application
after the natural and simulated rainfall events, the total and marketable yields were
lower than 23.5 T ha-1 and 19.0 T ha-1, respectively, with at least 21.2% yield reduction
from the 30 year (1976-2006) average marketable yield (24.1 T ha-1) for seepage-
irrigated spring potato crop around Hastings. Sufficient N level plays an important role to
stimulate tuber growth and insure optimum yield (Zebarth and Rosen, 2007). Generally,
N requirement of potatoes slightly increases during tuber initiation stage with the highest
N requirement occurring at the tuber bulking stage (Ojala et al., 1990). Potato at 20-25
cm and full flowering growth stages are tuber initiation and bulking stage, respectively.
The level of precipitation over 2008 growing season was 27.3 cm, which was close to
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the historical average of 27.4 cm (Pack et al., 2006). The 5 cm rainfall was not a
leaching rain according to UF IFAS definition of leaching event (7.6 cm in 3 days or 10.0
cm in 7 days). However, the natural and simulated 5 cm rainfalls that occurred during
those two critical growth stages attributed to significant yield reductions.
Plants fertilized with PSCU and PCU produced the highest total and marketable
yields (23.9 and 18.9 T ha-1; 21.2 and 17.2 T ha-1, respectively). Plants fertilized with
UFs produced the lowest total and marketable yields (17.5 and 13.7 T ha-1; 17.8 and
14.0 T ha-1 for UF1, 2, respectively). The lower yield of plants with UF treatments may
be attributed to the slow release characteristic of these two fertilizers. Also, the
fumigation is widely applied annually around 3 weeks prior to planting, which
approximately significantly reduce soil microbial population. Since microbial activities
are required by UFs to decompose complex molecular structure to release N, the
applicability of UFs may be limited for short growing season crops with soil fumigation
practice (Morgan et al., 2009). Similar results had been reported by Chen et al. (2008)
for lower yield performance than other CRFs using two split application of UF fertilizers.
Tuber SG is considered as an important quality character by the potato chip
industry. High tuber specific gravity (SG) generally increases quality and yields of chips.
The premium price for tubers with high SG in purchase contract provides growers
incentive to apply cultural practice to increase SG. Tuber SG values under PSCU, PCU
were above 1.082, the averaged SG (1.079) for ‘Atlantic’ Potato at Hastings research
farm (Hutchinson et al., 2002b). Tubers SG values from plants fertilized with UFs were
the lowest with value at 1.078. There was no significant difference for tuber external and
internal quality (Table 6-3) among CRF treatments. The percentage of decayed tubers
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from plants fertilized with each treatment was high due to two critical potential leaching
events at plant 20-25 and full-flower growth stages. The 5 cm rainfalls washed soil from
row, resulting in more tubers being exposing. The high air and soil temperature in the
late season and rainfalls contributed to significantly more decayed tubers (Worthington
et al., 2007).
Nutrient Concentration and Leaching
At 20-25cm stage, collected leachate quality (nutrient content) was significantly
affected by the fertilizer program under the 5 cm natural rainfall events (Table 6-4).
Leachate collected from the plots fertilized with PSCU had the greatest NO3-N
concentration and NO3-N leaching (24.4 mg L-1 and 12.4 kg ha-1, respectively).
Leachate collected from plots fertilized with PCU, UF1, and UF2 had similar NO3-N
concentration (1.6, 1.5 and 3.5 mg L-1 for respectively). The maximum contaminant
concentration for NO3-N is 10 mg L-1 (USEPA, 2003). The difference between PSCU
and other CRFs was attributed to different release rate and mechanisms. Most PSCUs
are formulated by applying additional thin layer of an organic polymer (thermoplastic or
resin) outside of a sulphur-coated urea (SCU). Therefore, N release of PSCU was less
temperature sensitive than most PCUs (Sartain, 2004). Shaviv (1996) reported N
release of a PSCU had an initial “burst” of more than 20% of total N content. PSCU was
also reported to be able to release significant amount of N under low temperature in a
CRF evaluation study under controlled temperatures (Ph D disseration, Chen 2009).
The high initial N release of PSCU at the early grow season suffered from N losses
under the heavy rainfall.
In contrast, N release of PCU is primarily affected by soil temperature and not
moisture (Gandeza et al., 1991). Potatoes in Florida are grown as temperature is
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increasing during growing season. The temperature based release of PCU resulted in a
lower release rate in early season and a faster N release rate at late season when soil
temperature was higher, resulting in less NO3-N leaching (1.6 mg L-1). These results
would support the release pattern of PCU applied in early season (early Feb)
synchronize plant N demand better while reducing NO3-N losses. Shoji and Kanno
(1994) reported that the time pattern of macro-nutrients uptake such as N was generally
sigmoidal. N release curves from most PCUs are generally linear or sigmoidal, which
synchronize more with plant N demand (Shaviv, 1996).
However, when leachate with high NO3-N concentration are moved into perched
water, dilution may occur due to continuous irrigating of the seepage system. This may
result in minimal differences observed for perched water quality between fertilizer
treatments (Pack et al., 2006). Also, N leaching values measured from the ceramic cup
lysimeter-based N leaching was reported to be lower than from drainage lysimeters
(Zotarelli et al., 2007).
At full-flower stage, there was no significant difference for collect leachate water
quality (N concentration and load) between CRFs (Table 6-5). However, the NO3-N
concentrations in leachate samples were generally higher than at 20-25cm growth
stage. This may suggested that the rainfall intensity must also be considered for of NO3-
N leaching (Olson and Maynard, 2003). The simulated 5 cm rainfall (in 2 hours) at full-
flower stage created greater leaching force than natural rainfall (in 2 days). The minimal
difference of NO3-N leaching at this stage between fertilizer treatments may be
attributed to less difference of soil N availability at late season than early season. Also,
simulate rainfall (5 cm) in this study may not be sufficiently intensive for a strong
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leaching force, as leaching rainfall was defined as 7.5 cm in 3 days or 10.0 cm in 7 days
(Kidder et al., 1992). There was a potential early N loss at 11 DAP under an 8.1 cm
leaching rainfall, resulting in less available soil N at late season (Figure 6-1).
Overall, though the 5 cm natural or simulated rainfalls were not leaching events,
the significant NO3-N leaching may result in yield losses. The timing and intensity of
rainfalls played an important role for NO3-N leaching.
Soil Nutrient Analysis
In 2008, the soil analysis results (Table 6-6) indicated that there was no significant
difference for NH4-N or NO3-N concentration between CRF treatments after each
leaching event. However, soils from plots fertilized with the PSCU tended to have lower
NO3-N concentration as compared to other CRF due to greater NO3-N leaching in early
season. The similarity of soil N concentration indicated the less difference of soil N
availability between fertilizer treatments before the simulate 5 cm rainfall at full-flower
stage.
The soil NO3-N concentrations from each treatment after the leaching events were
lower than 20 and 15 mg kg-1 at 20-25 cm and full-flower growth stages, respectively.
The levels of soil NO3-N were considered lower than sufficient soil NO3-N range for
optimum yields (tuber initiation: greater than 20 mg kg-1, NO3-N for tuber bulking: 15~20
mg kg-1), resulting in the low yields (Stark and Westermann, 2003). This reinforced that
the 5 cm rainfall occurred at two critical growth stages may be attributed to the
significant reduction in soil NO3-N concentrations. The insufficient soil N levels indicated
a high probability that potato crop respond to the supplementary application of N
(Rodrigues, 2004). This suggested Florida BMP for supplemental additional N after
leaching events may also need to be combined with soil N sufficiency test. The leaching
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amount, timing and intensity should not be considered alone to direct the fertilizer
practices. Also, fertilizer source may need to be considered if determining the critical
value of soil NO3-N (Wilson et al., 2009).
Conclusions
In conclusion, the drainage lysimeters developed in this study can be used to
successfully determine in row nutrient movement into the perched water table. Plants
fertilized with PCU and PSCU produced higher total and marketable yields than plants
fertilized with UFs. However, leachate samples collected from plots fertilized with PSCU
in early season had significantly highest NO3-N concentration and leaching than PCU.
The results would support the use of PCU over PSCU with early season application
regarding reducing NO3-N leaching for Florida potato production. The UFs are not
appropriate fertilizers because of its slow release and the Florida soil fumigation
practice.
The 5 cm rainfall was not a ‘leaching event’ according to UF IFAS definition.
However, 5 cm rainfall occurred at critical potato growth stage significantly reduced soil
NO3-N concentration lower than sufficiency range, resulting in the yield reduction. The
future BMP research and development need to combine the leaching timing, force, and
tissue test to direct supplemental fertilizer practice. The nutrient loading into perched
water table may not be recovered by plants in the growing season, which is concern for
contamination of ground water.
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Table 6-1. Fertilizer formulation, manufacturer, nitrogen form, and water solubility.
zPSCU: polymer sulfur coated urea; PCU: polymer coated urea; UF: Urea formaldehyde yPecent N-P2O5-K2O Table 6-2. Tuber yield, size distribution and specific gravity for potato cultivar ‘Atlantic’
grown with differing fertilizer treatments and under a natural and simulated rainfalls (5 cm) at the University of Florida Hastings farm, FL in 2008.
Total yield Marketable yieldy Size distribution by class (%)x
Fertilizerz (T ha-1) (T ha-1) B A1 A2 A3 SG PSCU 23.2 aw 18.9 a 7 63 16 13 ab 1.084 a PCU 21.2 a 17.2 a 6 64 12 17 a 1.082 a UF1 17.5 b 13.7 b 10 65 10 12 ab 1.078 b UF2 17.8 b 14.0 b 11 71 11 5 c 1.078 b
zPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; UF: urea formaldehyde. yMarketable yield: size classes A1 to A3. xSize classes (cm): C = <3.8 cm; B = 3.8-4.8 cm, A1 = 4.8-6.4 cm, A2 = 6.4 cm-8.3 cm, A3 = 8.3 cm-10.2 cm, A4 = > 10.2 cm. wMeans separated within columns by Duncan Multiple range test at p ≤ 0.05. Means with the same letter are not significantly different ('ns').
Typez Formulationy Manufacturer Physical Characteristics
PSCU 38-0-0 Scotts Chemical Co. Granular Water insoluble
PCU 44-0-0 Agrium Fertilizers Granular Water insoluble
UF1 30-0-0 Georgia-Pacific Liquid Water soluble UF2 28-0-0 Helena Chemical Liquid Water soluble
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Table 6-3. External and internal defects for potato 'Atlantic' cultivar grown under several fertilizer treatments and under natural and simulated rainfalls (5 cm) at University of Florida Hastings farm, FL in 2008.
External tuber defects (%) Internal tuber defectsx (%)
Growth Mis- Sun- Rotten Total Brown Center
Fertilizerz cracks shapen burned & misc. cullsy HH BR CRS IHN L M H PSCU 0 0 6 5 12 0 0 0 0 4 0 1 PCU 0 0 7 5 12 0 0 0 1 3 0 0 UF1 0 0 7 4 11 0 0 0 8 4 1 0 UF2 0 0 7 3 10 0 0 0 1 3 0 0
zPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; UF: urea formaldehyde. yTotal culls are the sum of green, growth cracks, misshaped, and rotten categories as percentage of total yield Table 6-4. In-row leachate NH4-N, NO3-N and total Kjeldahl N (TKN) concentration and N leaching from several fertilizer
treatments after a natural 5 cm rainfall at potato 20-25 cm growth stage at University of Florida farm in Hasting, FL in 2008.
Concentration (mg L-1) Nutrient leaching (kg ha-1)
Fertilizerz NH4-N NO3-N TKN Volume (ml) NH4-N NO3-N Total N K PSCU 16.2 ay 24.4 a 16.3 a 660 6.3 12.4 a 18.4 67.8 PCU 2.6 b 1.6 b 6.1 b 913 1.4 0.7 b 3.6 82.3 UF1 7.4 b 1.5 b 10.4 ab 1644 4.7 0.2 b 7.1 144.2 UF2 2.6 b 3.5 b 5.5 b 1315 2.3 1.2 b 5.3 70.7
zPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; UF: urea formaldehyde. yMeans separated within columns by Duncan’s multiple range test at p ≤ 0.05.
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Table 6-5. In-row leachate NH4-N, NO3-N and total Kjeldahl N (TKN) concentration and N leaching from several fertilizer treatments after a simulated 5 cm rainfall at potato full flower growth stage at University of Florida farm in Hasting, FL in 2008.
Concentration (mg L-1) Nutrient leaching (kg ha-1)
Fertilizerz NH4-N NO3-N TKN K Volume (ml) NH4-N NO3-N Total N K PSCU 6.8 36.4 12.1 233.0 249 1.2 10.0 12.3 42.2 PCU 4.8 38.3 8.7 271.8 403 0.8 16.4 8.5 73.1 UF1 2.0 25.1 8.4 211.5 440 0.6 6.9 3.7 55.5 UF2 2.2 12.8 10.1 237.2 228 0.3 2.5 3.7 33.2
zPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; UF: urea formaldehyde. Table 6-6. Soil sample NH4-N and NO3-N concentration after a natural and simulated 5 cm rainfall at the University of
Florida Farm in Hastings, FL in 2008.
20-25 cm growth stage (mg kg-1) Full-flower growth stage(mg kg-1)
Fertilizerz NH4-N NO3-N P K NH4-N NO3-N P K
PSCU 1.44 8.80 81.9 58.5 0.69 6.57 79.3 60.4 PCU 2.37 19.53 81.4 70.2 1.74 11.46 70.7 48.6 UF1 0.56 10.17 83.2 79.2 0.88 3.19 81.9 101.1 UF2 0.71 12.94 86.2 88.4 1.89 5.21 78.8 51.0
zPSCU: polymer-sulfur coated Urea; PCU: polymer coated urea; UF: urea formaldehyde.
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Figure 6-1. Daily rainfall (cm) and average daily air temperature (60 cm) and soil temperature (10 cm depth) at University
of Florida Hasting farm, FL in 2008. The red arrows denote a 5 cm natural and simulated rainfall at 20-25 cm and full-flower stage respectively. The triangle dots denote planting and harvest dates.
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A B
C D
Figure 6-2. Lysimeter in the field and experiment design. A) The drainage lysimeter (composed of a 15 cm cup, a
drainage plate, and a 255 microns nylon screen). B) Simulated irrigation at full-flower stage. C) The drainage lysimeter in a plot with no-N control. D) A drainage lysimeter in a plot with PSCU.
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CHAPTER 7
SUMMARY AND CONCLUSIONS
The cultivated potato, (Solanum tuberosum L.) is one of the most important world
food crops. In Florida, potatoes (Solanum tuberosum L.) were grown for fresh market
and the chipping industry on 10,610 hectares at a value excess of $163 million in 2007
(USDA, 2007). Seepage-irrigated potato is one of important spring crops in northeast
Florida with high N demand for optimum production. The continuous open bed irrigation
system is vulnerable to NO3-N leaching combined with the shallow root system of potato
plants, soils with low nutrient holding capacity, and potential for leaching rainfall.
Best Management Practices (BMPs) are being developed to assist growers remain
profitable through adapting specific cultural practices while at the same time reducing
non-point source of pollution of surface and ground water. In the Tri-County Agricultural
Area (St. John’s, Putnam, and Flagler counties, TCAA) of northeast Florida, one of main
purposes to implement BMP, is to reduce NO3-N movement from agricultural land in St.
Johns river basin. However, synchronizing plant nutrient demand for an optimum plant
growth while reducing nutrient losses to surrounding environment remains a major
challenge in potato crop management. The use of controlled-release fertilizers (CRFs)
formulated to correspond with the N demands of plants may be a potential BMP to
achieve both production and environmental goals through appropriate application.
However, the suitable CRF source, rate and application timing are still under
investigation. The high cost per unit of fertilizer is a prime reason for restricting wide use
of CRFs. Manufacturers formulate CRFs using different materials and release
mechanisms without providing sufficient information that states release characteristics.
The difficulty to quantify nutrient and release rates among products becomes the
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challenge to develop a successful CRF program. The appropriate CRFs with accurate
release rate and patterns, compare the influence of CRFs to traditional soluble fertilizers
on potato production, environmental pollution, and develop the optimal application rates
for northeast Florida potato production needs to be determined.
To achieve this goal, the present research was conducted with four major
objectives i) evaluate N release rates from CRFs under laboratory conditions in order to
select the most promising CRF for field further evaluation; ii) determine the appropriate
fertilizer source and optimum N rate and influence of CRFs on perched water table
quality iii) compare the influence of different PSCU or PCU applications [CRF alone or
combination with ammonium nitrate (AN)] on potato production, tuber quality and
perched ground water quality through field evaluation; and iv) comparing the influence
of CRF source on in row N movement under leaching events.
The experiments were conducted at the University of Florida’s Hastings farm.
Experiment 1 (incubator study) was conducted to evaluate the release profiles
associated with soil temperatures. Six CRFs from two manufacturers were evaluated
under aqueous conditions at controlled temperatures from 5 to 30 °C over a 13-week
period. The cumulative N releases (CNRs) were analyzed to simulate the release rate
and prediction model of CRFs. N release of polymer coated ureas (PCUs) was strongly
affected by temperature while N release of PSCU was less temperature sensitive. P-
PSCU (polymer sulfur-coated urea, 420 g N kg-1, Purcell Technologies, INC) and H-
PCU2 (polymer coated urea, 420g N kg-1, Haifa Chemical, LTD) released N over 60 and
90 days, respectively. It was observed for PCUs that a portion N of the prill was not
released under normal field temperatures. This results in a long tail for the decay stage
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of a release curve. This was because a low nutrient concentration inside fertilizer prills
may decrease the driving force for nutrients out of the thick coating as N concentrations
reduced inside the prill. The same phenomenon was reported for CRF products before,
especially for those SCUs with thick coatings (Shaviv, 2005). The non-released N may
be a concern for high N concentrations remaining at the end of cropping season,
resulting in potential of pollution and lower N use efficiency. The linear formula (K=AT+B)
developed through this study described the relationship directly between release rate (K)
and temperature (T), where A and B are constants. The release prediction model
developed in this study also provided an accurate estimate of nutrient release of a CRF
over varying temperature under field conditions.
These results suggested that P-PSCU and H-PCU2 are potential fertilizer
candidates for short growing seasons in cool conditions, such as Florida early-spring
potato production. P-PSCU application may mirror a N split application of soluble N
resulting in higher nutrient use efficiency. However, the high initial N release of P-
PSCU under low temperature may also suffer from the nutrient losses in early season
under leaching events. The appropriate coating materials or technology are needed to
formulate polymer fertilizers are needed to avoid residual N remaining at the end of the
season. The appropriate PCUs for Florida potato production need to have a release rate
(K) average seasonal temperatures above 0.0230. However, the cost of most CRFs is 2
to 5 times higher than traditional soluble fertilizers (Trenkel, 1997). The high cost of
these CRFs may also limit the wide use due to lack of significant improvement of tuber
yields or quality.
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In experiment 2 (CRF field evaluation), four CRFs from different manufactures
were evaluated under field conditions. The treatments were a factorial combination of
fertilizer sources (AN, PSCU + Urea, P-PCUs, H-PCUs and MU) and fertilizer rates (112,
168 and 224 kg N ha-1). This experiment was a comparison of five fertilizer sources at
three levels of fertilizer rate.
The results from experiment 2 indicated that plants fertilized with NH4NO3 (AN)
had greater tuber quality than that from CRF fertilized plants in a growing season with
little leaching. Plants fertilized with PSCU + Urea or H-PCUs produced similar
marketable yields as NH4NO3 (AN) while plants fertilized other CRFs produced lower
yields. However, tubers from plants fertilized with these two CRFs had lower tuber
specific gravity than AN. Other CRFs examined in this study may lead to nutrient stress
and a reduction in tuber internal quality due to lower slow release rates. Plants fertilized
with methelyne urea (MU) produced the lowest tuber yields among fertilizer sources.
Within each fertilizer source, tuber yields increased linearly when N rate increased with
the greatest yields at 224 kg N ha-1. Generally, quadratic equations were found to best
describe the response of tuber yield to N fertilization rates because of a decline in tuber
yields with over application (Belanger et al., 2000). However, without higher N rates
added to this study, the optimum N rate to maximize yield can only be presumed to be
above 224 kg N ha-1. For perched water quality, NO3-N concentrations were found to be
less than the published pollution level (10 mg L-1) for water samples sampled 28 days
after planting (DAP).
These results suggested that the benefits of using CRFs were not realized in a
growing season without excessive rainfalls. Application timing is very important to
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reduce the risk of residual N after the cropping season is over. Also, the slow release
rate of CRFs may increase the risk of high incidence of tuber defects due to nutrient
stress. CRFs with fast release rate are more appropriate for Florida short growing
season. CRFs with N release depending on microbial activity have limited applicability
for Florida short growing season because of soil fumigation practices prior to planting
and cooler soil temperatures during the first 60 days after planting, resulting in low
yields.
Experiment 3 (CRF application program evaluation) compared the influence of
CRF application timing on potato production, tuber quality and perched water table
quality. The treatments were a combination of fertilizer sources (PSCU, PCU and AN)
and application timing (at fumigation, planting, hilling or a combination of application
timings). ‘Atlantic’ plants fertilized with PSCU (380 g N kg-1, Scotts LLC) and PCU (440
g N kg-1, Agrium INC) at 196 kg N ha-1 in 2007 produced comparable yields as the
historical (1976-2006) average potato marketable yields around Hastings area when
minimal leaching events occurred during the growing season. PSCU and PCU used in
this study were considered relatively inexpensive CRFs. For example, PCU was $ 0.20
more per kg N than soluble urea (Wilson et al., 2009) resulting in $44.8 more in fertilizer
cost per hectare at the maximum BMP N rate (224 kg ha-1). The higher cost of PCU
may be offset by reducing the application cost of sidedress soluble fertilizer, which is
$44 per hectare (Wilson et al., 2009). However, plants fertilized with PSCU and PCU in
2008 had N deficiency at both 20-25cm and full flower growth stage based on tissue
analysis when leaching events occurred in early season. This resulted in low yield.
Tuber yields were similar among fertilizer source between application programs,
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indicating a more flexible application timing. In 2007, the benefit of a split 70% N (PSCU)
at fumigation and planting then with supplemental 30% N by sidedress (AN) did not
improve yields when PSCU was used but improved yields for when PCU was. A
sidedress of AN was surface applied, to avoid root damage, then covered with soil,
resulting in nutrients placement above the plant root zone. This practice may slow the
potato plants response to N. The two split applications of CRF (at fumigation and
planting) increased tuber yields for plants fertilized with PCU by extending the release
period while it had minimal improvement for PSCU because of the slow N release of
PSCU. The differences on tuber yields between application programs were eliminated
by frequent heavy rainfall early season in 2008.
‘FL 2053’ plants had a similar response as ‘Atlantic’ to different fertilizer treatments.
Tuber yields of ‘FL 2053’ were greater for plants fertilized with a majority of PSCU as
the N sources applied in early season or PCU combined with AN. ‘Harley Blackwell’
plants had similar yields when fertilized with a majority of PSCU or PCU and combined
with AN. This indicated ‘Harley Blackwell’ may have lower N requirement in early
season compared to ‘Atlantic’ and ‘FL2053’. There were no significant differences for
tuber external or internal quality between fertilizer treatments for each cultivar. However,
when fertilized with CRFs, ‘Harley Blackwell’ and ‘FL 2053’ had more resistance to
internal heat necrosis (IHN) as compared to ‘Atlantic’ under stressful growth conditions
in 2008. The frequent rainfall in early season combined with high soil temperature late in
the season promoted the incidence of IHN in ‘Atlantic’ tubers because ‘Atlantic’ was
high susceptible to IHN.
160
For ‘Atlantic’ and ‘FL 2053’ potato production in TCA, PCU might be better be
applied prior to planting for a sufficient N release while PSCU could be applied at
planting to synchronize with plant N demand throughout the season. The relatively
lower in price of these two CRFs ($1.54 per kg N for PCU in 2009) may allow the
commercial use by producing comparable net return as using traditional soluble
fertilizers. Additional studies need to be conducted which exam varying rates of N above
196 kg N ha-1 and soluble N fertilizers.
Experiment 4 evaluated the influence of CRF source on in row N movement
under two potential rain events on potatoes in the 20-25 cm growth stage (5 cm natural
rainfall in 2 days) and full flower growth stage (5 cm simulating rainfall in 2 hours),
respectively. In Experiment 4, plants fertilized with PSCU and PCU produced
significantly greater marketable yields than Urea formaldehyde (UF) under the influence
of potential heavy rain events. Water samples collected from leachate in plots fertilized
with PSCU in the early season (35-45 DAP) had significantly higher NO3-N (higher than
10 mg/L) concentration and leaching because N release of PSCU was less temperature
sensitive with high initial N release at early season. There were similar NO3-N
concentrations in water samples from CRFs when the plants were at the full flower
stage. The 5 cm natural or simulating rainfall at both critical growth stages reduced soil
NO3-N levels below the sufficient range, resulting in the yield reduction. Under
conditions of potential heavy rainfall such as those that can occur in the TCAA every
year, higher levels of preplant N and sidedress N have to considered in order to
produce economical returns to potato producers.
161
Implications and Future Work
Based on the results from these experiments, it could be concluded that the
varying release rates of nutrient over season of CRFs increased the risk of reduction in
tuber yield and quality. A release formula and prediction model successfully simulated N
release rate of polymer coated fertilizers when temperature changed. Such a laboratory
evaluation can help to select the most promising PCUs for further field evaluation.
However, further development of a comprehensive prediction model may need to
consider other factors such as soil moisture and microbial activity. In the field evaluation,
the benefits of CRFs in yields or water quality were not realized in a growing season
without significant leaching events. Regardless of fertilizer source, NO3-N
concentrations of the perched water table were below maximum contamination in the
early season. Future research should monitor more frequently for NO3-N concentrations
of perched water table initialing prior to the first fertilizer application throughout the
season. Soluble fertilizers have the advantage of providing a rapid growth response
thus avoiding nutrient stress. PCU (440 g kg-1, Agrium INC) applied prior to planting
may synchronize plant growth demands better with while reducing the potential risk of N
losses under leaching events. PSCU (380 g N kg-1, Scotts LLC) applied at planting had
a high initial N release that might increase the risk of N losses in early season. CRFs
with their N release depending on microbial activity (UFs or MUs) are not appropriate
fertilizer sources for Florida potato produced in the TCAA because of short season,
fumigation uses and the cool temperature for the first 60 days after planting. Without
significant yield or tuber quality improvement, CRF usage may be limited because of
higher costs for N. Optimum N rate from this study appeared to be at or over 224 kg N
162
ha-1. Future research needs to address how N rates greater than 224 kg N ha-1 affect
yields and tuber quality. Surface application of sidedress N might delay the nutrient
availability. The investigation of optimum application methods (fertilizer source and
placement) of sidedress N will be beneficial in assisting potato plants response quickly
to supplemental N. Overall, the appropriate N fertilizer strategy for Florida potato
production is still under development and will require more understanding about the
balance between plant demand and nutrient supply over the entire growing season
under highly variable environmental conditions.
163
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BIOGRAPHICAL SKETCH
Zhiwei Chen was born in Fujian province, China. He graduated from China
Agricultural University in 1999 for a Bachelor degree in agriculture and biotechnology.
Then he worked for Frito-Lay China for four years in China as an agronomist. He was
trained for chipping variety potato growth in Baotou Modern Farm for a year, and then
he travelled very often to several provinces t such as Inner-Mongolia, Guangxi,
Guangdong, Shangdong for potato procurement projects. In 2003, he came to the North
Dakota State University studying for his master degree in Horticultural Sciences. His
research project was “Dakota Crisp and Dakota Diamond management strategies:
nitrogen fertilizer and chip processing quality”.
Zhiwei was enrolled as a Ph.D student in Horticultural Sciences in University of
Florida for his continue research on crop nutrient research from 2006 spring. He
received his Ph.D. from University of Florida in August 2010.
