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Soilless Culture Technology for High Quality Lettuce

D. Frezza, A. León, V. Logegaray and A. Chiesa Cátedra de Horticultura, Facultad de Agronomía Universidad de Buenos Aires Av. San Martín 4453 (C1417DSE) Argentina Corresponding author: D. Frezza

M. Desimone and L. Diaz Cátedra de Química Analítica e Instrumental Facultad de Farmacia y Bioquímica Universidad de Buenos Aires Junín 956 (1113) Argentina

Keywords: floating system, perlite, nitrates, inorganic cations, ascorbic acid Abstract

The aim of this research was to evaluate butterhead lettuce quality in a soilless culture system. Butterhead lettuce cultivar “Lores” was cultivated, and two experiments were performed. In the first, floating system (FS) and soil culture (SC) were compared in fall (autumn) prduction [2002 - 2003], while in the second, substrate culture (PC) (plastic gutter filled with perlite) with three different levels of calcium (0, 3, and 6 me L-1) in the nutrient solution were compared in spring production [2003]. Growing cycles varied according to the culture system. In general, plants harvested from the soilless culture had a lower dry weight and leaf area, however significant differences were observed in productivity. Nitrate content was significantly affected by the production system. Ascorbic acid content showed no differences resulting from treatments. Floating system results showed some variation between the two years of the experiment. Inorganic cation differences were observed between plant harvest from all systems, especially in K+ and Mg2+. Colour intensity changes between production systems were insignificant. No variation in incidence of tip-burn relating to different calcium levels was found in lettuce grown in perlite.

INTRODUCTION

Increased keeping quality or shelf life is one of the main aims of our research. Combining good shelf life with acceptable quality enables food to be distributed over greater distances and time periods, which is of central importance in a global market.

In recent decades much attention has been focused on the packaging and controlled-atmosphere storage of fresh produce. The current importance of supply chain quality and logistics will diminish as research increases our understanding of preharvest factors affecting postharvest quality (Chiesa et al., 2003). All factors affecting post-harvest performance must be integrated, including production systems, cultivars, fertilisation, salinity, irrigation, temperature, leaf expansion and maturity stage.

Cultivating leafy vegetables in a floating system is the easiest and cheapest means of production, since this system shows high water and fertiliser efficiency and low environmental impact (Gonnella et al., 2003). On the other hand, soilless culture allows direct control of the nutrient solution, making it possible to modify composition and concentration to achieve predictable results in relation to dry matter content, nitrate content or other organoleptic and structural (calcium) features of produce (Elias et al., 1999). Gonnella et al., (2001) found floating cultivation produced acceptable yield and good control quality parameters in baby leaf species (shorter growing cycles, improved uniformity of growth and automation of cultural techniques, in addition to providing high levels of hygiene and quality).

Solution composition can have a significant effect on leaf quality. Calcium is one of the most important nutrients and is associated with delayed plant senescence, stabilising influence on cell membranes, and the membrane lipid catabolism which is a characteristic feature of damaged, quiescent plant storage organ and fresh-cut produc. As a result the use of calcium has been suggested as a way to delay senescence in fresh-cut

Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005

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plant tissue (Picchioni et al., 1996). The aim of this research was to evaluate butterhead lettuce quality in a soilless

culture system. The goal was to achieve production of high quality lettuce in terms of commercial standards and shelf life in modified atmospheric conditions (SAGPyA, 2004). MATERIALS AND METHODS

The experiment was carried out in an unheated greenhouse in the experimental field of the Horticultural Department of the Faculty of Agronomy, University of Buenos Aires, Buenos Aires, Argentina.

Butterhead lettuce cultivar “Lores” was cultivated and two experiments were carried out: Experiment 1

Floating system (FS) (100 cm x 250 cm x 40 cm width x length x height) and soil culture (SC) were compared in fall (autumn) production [2002 - 2003]. Plants were cultivated in polystyrene containers (1.5 inch thick). The nutrient solution was oxygenated using an air pump to introduce tiny bubbles. Experiment 2

Substrate culture (PC) (plastic gutter filled with perlite-500 cm x 40 cm x 30 cm, length x width x height) with three different levels of calcium (0, 3, and 6 me.L-1) in the nutrient solution were compared, in spring production (2003).

The plants were transplanted at a density of 39 plants.m-2 (FS), 18 plants.m-2 (PC) and 10 plants.m-2 (SC).

Two nutrient solutions were used, one for the floating system (Casas Castro, 1999) and the other for the substrate culture in accordance with the conclusions/recommendations of Ki-Young et al., (2001) for butterhead lettuce.

The nutrient solution temperature, pH and CE (dS.m-1) were controlled. Air temperature, relative humidity and solar radiation intensity inside the

greenhouse were recorded hourly with a datalogger (Hobo). Treatments were arranged in a randomised complete block design with three

replicates. Lettuce were harvested and measured for fresh and dry weight, leaf length and

width, leaf length and width ratio, leaf area (Yoshida et al., 1997), leaf number, aerial and root biomass ratio and ascorbic acid, NO3-, K+, Ca2+, Mg2+, Na+ by capillary electrophoresis (Pañak et al., 1998, Ito et al., 2003).

A Minolta CR 300 chromameter was used. Colour was quantified in the L*, a*,b* colour space, Chroma [C*= (a*2 + b*2 )0.5 ] and hue angle [hº = tan-1 (b*/a*)].

During the growth cycle the incidence of tip-burn was monitored (Kader et al., 1973).

Data were subject to the SAS (Cary, NC) general lineal model procedure. Treatment mean values were compared with the Tukey test (p<0.05).

At harvest, according to experiments, intact leaves were packed in multilayer polyolefin bags and stored in a chamber at 1º and 8 °C for 7 days. Samples were taken at 0, 2, 4 and 7 days after harvest and postharvest quality was evaluated. (Data not shown). RESULTS AND DISCUSSION Effect of Soilless Culture (Floating System vs. Soil Culture)

Both years showed similar results on growth parameters. At harvest, the soil culture plants had higher aerial fresh and dry weight, leaf area, aerial:root biomass ratio, length and width (p=0.0003) than the floating system plants (Table 1). Siomos et al., (2001) obtained similar results in butterhead lettuce cultivated in perlite.

In lettuce from hydroponics culture, lower levels (fresh weight) in K+ (-38.7 %) (p= 0.03), and ascorbic acid (-72 %) (p= 0.0015) were found in the second year. Table 2.

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Nitrate content was significantly affected by the production system, with lower levels found in the FS plants(2002=-73%, 2003=-26%) than in the soil culture plants (p= 0.0001). In spite of this variation, nitrate content was still below critical levels in each production season. (European Commission, 1997) (Table 2).

Siomos et al., (2001) found plants from a soilless culture had higher nitrate, total nitrogen, phosphorus and potassium content compared with plants harvested from soil culture. No significant differences in calcium content were observed between plant harvest from the soilless and the soil culture.

Ascorbic acid content in lettuce leaves from FS was higher (+72 %) than lettuce from greenhouse soil (Table 2).

Increasing the amount of nitrogen fertiliser decreased the vitamin C content. Plant growth is generally enhanced by nitrogen fertilisation so a relative dilution effect may occur in the plant tissues. Nitrogen fertilisers are also known to increase plant foliage and thus may reduce the light intensity and accumulation of ascorbic acid in shaded parts. Since excess use of nitrogen fertilisers increases the concentration of nitrate and simultaneously decreases that of ascorbic acid, it may have a double negative effect on the quality of plant foods. (Lee and Kader, 2000).

There was anegative correlation between nitrates and ascorbic acid content. Lettuces grown in soil were lower in ascorbic acid content than those grown in hydroponics.

Low NO3 level (9,5 me.L-1) in nutrient solution was used. This could explain the ascorbic acid content. Similar results were found by Sorensen et al., (1994).

The data obtained by capillary electrophoresis method showed high variability. It is probable that dilution and temperature in the auto-sampler influenced the capillary electrophoresis. Ito et al., (2003) recommended nitrates be determined with 100 fold dilution at 24 ºC in the auto sampler. Kawashima and Valente Soares analysed inorganic cations in butterhead lettuce by flame absorption spectrometry. The data showed high variation compared with results obtained in this research [K+:318, Na+: 5, Ca2+: 47, Mg2+: 18 (mg.100 g-1 FW)].

Colour intensity changes showed no significant differences between production methods (Table 3). Effect of Different Calcium Concentrations in Nutrient Solution

The highest aerial (p<0.0001) and root fresh weight (p=0.008), leaf number (p=0.02), leaf area (p<0.0001) and aerial:root biomass ratio (p<0.0041) was obtained when nutrient solution was 6 me.L-1 .

K+ (p=0.01) and Mg2+ (p=0.02) levels (fresh weight) were lower with 6 me.L-1 in the nutrient solution than treatments with 0 and 3 me.L-1.

No incidence of tip-burn was found as a result of temperature, humidity and growth rate during the growth cycle [Score= 1(none)-2(slight) degree of severity].

Colour intensity changes showed no significant differences related to different calcium concentrations (Table 3).

Well-known consequences of calcium imbalances include bitter pit in apples, blossom end rot in tomatoes and tip-burn in lettuce. Calcium deficiency is often the consequence of insufficient Ca translocation to the desired organs. Previous research has focused on factors related to or affected by environment, such as growth rate, transpiration, solution salinity and root pressure.

Positive effects were found when calcium was increased in nutrient solution. The calcium content of the whole plant was different in different plant organs and growth stages. Both dry matter and Ca content in leaves were much higher than other organs in lilium (Chien Chang and Miller, 2003). Mature leaves in cucumber are the strongest sinks for Ca, accounting for 70% of the total above-ground accumulated calcium. (Ho and Adams, 1994).

This information provides evidence that principal calcium accumulation in leafy vegetables takes place in leaves and may vary according to plant maturity. Leaf

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senescence inbutterhead lettuce could, therefore, be delayed by increased application of calcium in nutrient solution or by foliar feeding or immersion. These results allow us to advance the possibility of managing different cultural systems to obtain high quality lettuce, meetingcommercial standards and minimising processing requirements in modified atmosphere conditions. (SAGPyA, 2004). Literature Cited Casas Castro, A. 1999. Formulación de la solución nutritiva. Parámetros de ajuste. En

Cultivo sin suelo II. Curso superior de Especialización. Ed. Fernández Fernández, M. and Cuadrado Gomez. I.M. Almería. España. 590 pp.

Chien Chang, Y. and Miller, W.B. 2003. Growth and calcium partitioning in LiliumStar Gazer in relation to leaf calcium deficiency. J. Amer. Soc. Hort. Sci. 128(6):788-796.

Chiesa, A., Frezza, D., Fraschina, A., Trinchero, G., Moccia, S. and Leon, A. 2003. Pre-harvest factors and fresh cut vegetables quality. Acta Hort. 604:153-159.

Elia, A., Serio, F., Gonnella, M and Santamarina, P. 1999. Growing nitrate free endive in soilless systems. Acta Hort. 481:267-271.

European Commission, 1997. Commission regulation (EC) Nº 194/97 of 31st January 1997. Official journal of the European Communities Nº 131/48-50

Gonnella, M., Serio, F., Conversa, P. and Santamarina, P. 2003. yield and quality of lettuce grown in floating system using diferent sowing density and plant spatial arrangements. Acta Hort. 614:687-692.

Ho, L.C. and Adams, P. 1994. The physiological basis for high fruit yield and susceptibility to calcium deficiency in tomato and cucumber. J. Hort. Sci. 69:367-376.

Ito, H., Horie, H., Nagai, Y., Ippoushi, K., D. and Azuma, K. 2003. The determination of nitrate in spinach and Japanese radishes by Rqflex, portable ion electrode (pIE, high performance liquid cromatography (HPLC) and high performance capillary electroforesis (CE): Acta Hort. 604:545-548.

Kader, A.A., Lipton, W.J. and Morris, L.L. 1973. Systems for scoring quality of harvested lettuce. HortScience. Vol 8 (5):408-409.

Kawsahima, L.M. and Valente Soares, L.M. 2003. Mineral profile of raw and cooked leafy vegetables consumed in soutern Brazil. Journal of food composition and analysis 16:605-611

Ki-Young, C. and Yong-Beom, L. 2001. Effect of salinity of nutrient solution on growth, translocation and accumulation of 45Ca in butterhead lettuce. Acta Hort. 548:575-580.

Lee, S.K. and Kader, A.A. 2000. Preharvest and postharvest and postharvest factors influencing vitamin C content of horticultural crops. Postharvest Biology and Technology 20 (3):207-220.

Pañak, K., Giorgeri, S., Ruiz, O. and Díaz, L.E. 1998. Postharvest analysis of vitamin C content and inorganic cations in lettuce by CZE. Journal of Capillary Electrophoresis, 5:59-63.

Picchioni, G.A., Watada, A.E. Whitaker, B.D. and Reyes, A. 1996. Calcium delays senescence related mee lipid changes and increases net synthesis of meme lipid components in shredded carrots. Postharvest Biology and Technology 9:235-245

SAGPyA. 2004. La cadena de las hortalizas frescas y minimamente procesadas. Buenas prácticas de manufactura. Disponible en http//www. sagpya.mecon.gov.ar/.

SAS. 1999. Institute Inc. SAS/Stat user’s guide release 6,12 Edition, Carry, NC (USA): SAS Intitute Inc.

Siomos, A.S., Beis, G., Papadopoulou, P.P. and Barbayiannis, N. 2001. Quality and composition of lettuce (cv. “Plenty”) grown in soil and soillless culture. Acta Hort. 548:445-449.

Siomos, A.S., Beis, G., Papadopoulou, P.P., Nasi, P., Kaberidou, I. and Barbayiannis, N. 2001. Aerial biomass, root biomass and quality of four lettuce cultivars grown hydroponically in perlite and pumice. Acta Hort. 548:437-443.

Sorensen, J.N., Johansen, A.S. and Poulsen, N. 1994. Influence of growth conditions on the value of crisphead lettuce. Marketable and nutritional quality as affected by

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nitrogen supply, cultivar and plant age. Plant Foods for Human Nutrition 46:1-11 Yoshida, S., Kitano, M. and Eguchi, H. 1997. Growth of lettuce plants (Lactuca sativa L.)

under control of dissolved O2 concentration in hydroponics. Biotronics, 26: 39-45. Tables Table 1.Yield of butterhead lettuce plants by experiments at the end of the growing cycle.

Root

Dry weight Leaves

g.plant

Biomass ratio

(Plant)

Days after transplanted

Yield (kg.m-2)

Number Total leaf area

(cm2)

Fresh weight

Leaves

Root

Experiment 1 2002 Soil Floating system

1.36b 2.18a

21a 19a

4682.1a 1770b

9.83a 4.47b

10.76a 6.92b

0.76a 0.75a

13.83a 2.61b

45 28

2003 Soil Floating system

3.68a 4.04a

28a 23a

6983.6a 2619.6b

15.83a 12.87a

13.15b 6.32a

1.21a 1.05a

22.95a 8b

60 38

Experiment 2 Calcium levels

(me.L-1) 0 3 6

2.0b 2.57ba 3.04a

20b 23ba 25a

2576.7b 3062ba 3327.6a

16.7ba 12.3b 19.4a

8.3a 7.1ba 5.9b

1.46a 1.1b 1.56a

5.68a 6.45a 3.78b

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Different letters denote significant differences between averages (p<0.05) Table 2. Inorganic cations, nitrates and ascorbic acid contents in butterhead lettuce leaves

(mcg. g-1 FW).

NO3- Na+ K+ Mg2+ Ca2+ Ascorbic

Acid Experiment 1 2002 Soil Floating system

1028.7b 273.6a

155.3a 123.5a

1204.2a 1119.5a

12.06a 9.91b

103.8a 95.62a

47.54a 52.45a

2003 Soil Floating system

218a 162b

438.9a 37.7b

673.7b 1100a

60.23a 46.3a

375.23a 106.7b

11.35b 38.96a

Experiment 2 Calcium levels (me.L-1) 0 3 6

49.06a 47.13a 37.23b

52.13a 41.66a 23.3a

1467.7a 971.5ba 516.6b

89.57a 65.9ba 44b

65b 108.9a 94.53ba

101.16a 104.73a 100.16a

Different letters denote significant differences between averages (p<0.05)

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Table 3. Colour intensity changes in leaves according to treatments.

L a b h c Experiment 1 2002 Soil Floating system

51.77a 53.92a

-18.08a -20.05a

33.22a 38.61a

118.6a 117.5a

37.82b 43.52a

2003 Soil Floating system

44.66b 57.5a

-15.37b -20.37a

30.19a 38.65a

116.8a 117.8a

33.89b 43.70a

Experiment 2 Calcium levels (me.L-1) 0 3 6

56.34a 55.47a 53.91a

-19.31a -19.67a -20.19a

36.96a 35.08a 33.91a

117.53b 119.83a 120.1a

41.7b 40.47a 39.21a

Different letters denote significant differences between averages (p<0.05)