Holden Research and Consulting
Cool Season Vegetables andStrawberry Response to Phosphates– Research and Observations over
the last Ten YearsDavid Holden
Holden Research and Consulting
Holden Research and Consulting
Introduction
• My Experience– Over 700 trials in the past ten years in nutrient
and pest management for fruit, nut, and vegetable production.
– Over 35 trials in the past ten years with phosphate based fertilizers on vegetables, strawberries, grapes, and trees.
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Introduction
• All phosphate trials were conducted in the coastal counties of Monterey, San Luis Obispo, Santa Barbara, and Ventura
• Both ortho and poly – phosphates were involved.
• Sometimes “organic acid” additives were involved, along with phosphorus “protecting” products.
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University Recommendations
University of California, ANR Publication 8098, Nutrient Management In Cool Season Vegetables
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What are the Issues withPhosphorus Availability
• pH
• Temperature
• Cation inhibition– Calcium
– Zinc
– Etc.
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How Soil pH affects P2O5
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Cool Soils
• Cool soils may induce phosphorus deficiency
• With cool soils you have slower root growth and development
• Less opportunity for roots to come in contact with the phosphorus they need at this time
• Limiting phosphorus in cool seasons exacerbates the ability for cool season vegetables to grow.
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Cation Inhibition
• Calcium and zinc cations (and others) have an affinity for PO4, phosphate anion.
• They form calcium and zinc phosphate precipitates which are now hard to resolubilize for root uptake.
• But this also helps reduce leaching of PO4
from the soil solution.
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Plant Phosphorus Utilization
• Forms nucleic acids (DNA and RNA)
• Used in the making of the chemical energy molecules of ATP and ADP.
• Through this transfer of chemical energy it is utilized in new growth and reproduction.
• Note that dry leaf analysis of P2O5 in young leaves is always higher than that found in older leaves.
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Symptoms of PhosphorusDeficiency
• Slow growth, stunted plants
• Purplish coloration on foliage of some plants (older leaves first)
• Dark green coloration
• Delayed maturity
• Poor fruit or seed development
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Not So Obvious Symptoms ofPhosphorus Deficiency
• Poor root development
• Reduced production– Sizing reduction
– Fruit set reduction
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Phosphate vs. Phosphite orPhosphoric Acid vs. Phosphorous
Acid• One is the source for a fertilizer, the other is
a source for a fertilizer and a fungicide.
• PO4 vs. PO3. PO3 will (?) oxidize eventually to PO4
• Know the difference. There is still quite a bit of confusion regarding these source products
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Four Recent Trials withPhosphates in Peppers and
Strawberries.• Phosphates generally placed in addition to
the grower’s standard practices which may include pre-plant and in-season phosphate applications.
• All crops grown on tape, which allows for precise in season placement of phosphate.
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Early Spring 2010 Peppers
• Pre-Plant poly phosphate applied as band under seedline on 4/27/10
• Pre-Plant Phosphorus (Olsen Method) – 41 ppm
• Treat 1 – untreated
• Treat 2 – 100 lb/ac P2O5 as 10-34-0
• Treat 3 – 55 lb/ac P2O5 as Proprietary
• Treat 4 - 30 lb/ac P2O5 as Proprietary
• Planted 5/5/10
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Lbs./Plant
UTC 1.6
Reduced Propietery 2 1.6
Reduced Propietery 1 1.8
Grower Standard 2.3
0.0
0.5
1.0
1.5
2.0
2.5
Po
un
ds
of
Fru
it
Chart 1: 2010 Spring - Summer Bell Pepper Phosphate Study -Camarillo, CA. - Total Yield per Plant
b
a
bab
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Post Treat Soil P2O5 Levels
• Treat 1 – 30 ppm
• Treat 2 – 31 ppm
• Treat 3 – 34 ppm
• Treat 4 – 27 ppm
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Late Spring 2010 Peppers
• Pre-Plant poly phosphate applied as band under seedline on 6/17/10
• Pre-Plant Phosphorus (Olsen Method) – 44 ppm
• Treat 1 – 125 lb/ac P2O5 as 10-34-0
• Treat 2 – 100 lb/ac P2O5 as 10-34-0
• Planted 6/20/10
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Lbs./Plant
100 lb P2O5 2.1
125 lb P2O5 2.2
0.0
0.5
1.0
1.5
2.0
2.5
Po
un
ds
of
Fru
it
Chart 2: 2010 Late Spring - Summer Bell Pepper Phosphate Study -Camarillo, CA. - Total Yield per Plant
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Post Treat Soil and Leaf P2O5
Levels• Treat 1 – 40 ppm
• Treat 2 – 49 ppm
• Leaf Treat 1 - .32%
• Leaf Treat 2 - .35%
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2008-09 Strawberries• Planted 10/2/08
• All Received Pre-Plant and in-Season Phosphate
• 500 lb/ac 18-8-13 slow release
• Approximately 20 gal/ac Phosphoric acid in season (150 lb P2O5) in tape
• Experimental Treatment received another 80 lb/ac of P2O5 in the tape and 40 lb/ac of P2O5
foliar as Proprietary Product
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Plant Sizing at Nine Weeks afterPlanting
Grower Standard
Additional Phosphate
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Tra
ys
pe
r Ac
re (
10
lb
. e
qu
iva
len
t)
Pick Day
Chart 6: Proprietery 2008-09 Strawberry Nutrient Study - Camarillo, CA. - Cumulative Marketable Production by Pick Day
Grower Standard
Proprietery
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ys
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r A
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nt)
Pick Day
Chart 6: Proprietery 2008-09 Strawberry Nutrient Study - Camarillo, CA. - Early Cumulative Marketable Production by Pick Day
Grower Standard
Proprietery
155 flats ahead
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ys
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r A
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Pick Day
Chart 6: Proprietery 2008-09 Strawberry Nutrient Study - Camarillo, CA. - Late Cumulative Marketable Production by Pick Day
Grower Standard
Proprietery
57 flats behind
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Conclusions
• Additional Early Season applications of P2O5 did help increase early season production
• As soils warmed and crop finished out the end season differential was not as great
• Early season production does return the grower a better price per flat.
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2009-10 Strawberries• Planted 10/3/09
• All Received Pre-Plant and in-Season Phosphate
• 500 lb/ac 18-8-13 slow release
• Approximately 20 gal/ac Phosphoric acid in season (150 lb P2O5) in tape
• Experimental Treatment received another 45 lb/ac of P2O5 in the tape as 3-18-18 (ortho phosphate) over five applications
• Also Proprietary product run alone and in combination with 3-18-18
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Plant Sizing at Nine Weeks
Grower Standard
Product A
3-18-18/Product A
3-18-18
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Tra
ys
pe
r A
cre
(1
0 lb
. e
qu
ival
ent)
Pick Day
Chart 8: Proprietery Trial on Strawberries - Ventura County, Fall/Winter 2009-2010 - Cumulative Marketable Production by Pick Day
Product A/3-18-18 Product A Alone Grower Standard 3-18-18 Alone
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0.0
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ys
pe
r A
cre
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uiv
ale
nt)
Pick Day
Chart 8a: Proprietery Trial on Strawberries - Ventura County, Fall/Winter 2009-2010 - Cumulative Marketable Production by Pick Day
Product A/3-18-18 Product A Alone Grower Standard 3-18-18 Alone
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0.0
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14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Tra
ys p
er A
cre
(10
lb. e
qu
iva
len
t)
Pick Day
Chart 8a: Proprietery Trial on Strawberries - Ventura County, Fall/Winter 2009-2010 - Cumulative Marketable Production by Pick Day
Product A/3-18-18 Product A Alone Grower Standard 3-18-18 Alone
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-$2,500.00
-$2,000.00
-$1,500.00
-$1,000.00
-$500.00
$0.00
$500.00
$1,000.00
$1,500.00
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12/1
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Do
llars
pe
r A
cre
-G
ros
s (
do
es
no
t in
clu
de
co
st
of
pro
gra
m
Pick Day
Chart 9:Proprietery Trial on Strawberries - Ventura County, Fall/Winter 2009-2010-Cumulative Differential from Grower Standard Return
Product A/3-18-18 Product A Alone 3-18-18 Alone
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Conclusions
• Additional Early Season applications of P2O5 did help increase early season production
• Spring of 2010 was cooler than previous spring. With phosphate source removed in February, reduction in production was observed.
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General Conclusions
• General production increases of 5-10% for coastal vegetables and strawberries when additional phosphate added to the growers standard programs in the fall, winter and early spring.
• These have occurred on soils that are not generally P2O5 deficient. 40-100 ppm P2O5 soils
• Similar results not observed in the summer time.
• No surprise that we are seeing a response on colder soils
• It is a surprise that what the grower’s thought was sufficient supplies of phosphorus was not so.
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Thank You!