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This article was downloaded by: [Pontificia Universidad Catolica de Chile] On: 06 September 2011, At: 18:04 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Vegetable Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/wijv20 Evaluation of Hydroponic Techniques on Growth and Productivity of Greenhouse Grown Bell Pepper and Strawberry M. Albaho a , B. Thomas a & A. Christopher a a Kuwait Institute for Scientific Research, P.O. Box 24885, 13109, Safat, Kuwait Available online: 11 Oct 2008 To cite this article: M. Albaho, B. Thomas & A. Christopher (2008): Evaluation of Hydroponic Techniques on Growth and Productivity of Greenhouse Grown Bell Pepper and Strawberry, International Journal of Vegetable Science, 14:1, 23-40 To link to this article: http://dx.doi.org/10.1080/19315260801890492 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms- and-conditions This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan,

Evaluation of Hydroponic

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Page 1: Evaluation of Hydroponic

This article was downloaded by: [Pontificia Universidad Catolica de Chile]On: 06 September 2011, At: 18:04Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

International Journal ofVegetable SciencePublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/wijv20

Evaluation of HydroponicTechniques on Growth andProductivity of GreenhouseGrown Bell Pepper andStrawberryM. Albaho a , B. Thomas a & A. Christopher aa Kuwait Institute for Scientific Research, P.O. Box24885, 13109, Safat, Kuwait

Available online: 11 Oct 2008

To cite this article: M. Albaho, B. Thomas & A. Christopher (2008): Evaluation ofHydroponic Techniques on Growth and Productivity of Greenhouse Grown Bell Pepperand Strawberry, International Journal of Vegetable Science, 14:1, 23-40

To link to this article: http://dx.doi.org/10.1080/19315260801890492

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching and private study purposes.Any substantial or systematic reproduction, re-distribution, re-selling, loan,

Page 2: Evaluation of Hydroponic

sub-licensing, systematic supply or distribution in any form to anyone isexpressly forbidden.

The publisher does not give any warranty express or implied or make anyrepresentation that the contents will be complete or accurate or up todate. The accuracy of any instructions, formulae and drug doses should beindependently verified with primary sources. The publisher shall not be liablefor any loss, actions, claims, proceedings, demand or costs or damageswhatsoever or howsoever caused arising directly or indirectly in connectionwith or arising out of the use of this material.

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International Journal of Vegetable Science, Vol. 14(1) 2008Available online at http://ijvs.haworthpress.com

© 2008 by The Haworth Press, Inc. All rights reserved.doi:10.1080/19315260801890492 23

WIJV1931-52601931-5279International Journal of Vegetable Science, Vol. 14, No. 1, Feb 2008: pp. 0–0International Journal of Vegetable Science

Evaluation of Hydroponic Techniques on Growth and Productivity of Greenhouse

Grown Bell Pepper and StrawberryAlbaho, Thomas, and ChristopherInternational Journal of Vegetable Science M. Albaho

B. ThomasA. Christopher

ABSTRACT. Conventional soil-based cultivation systems are not waterefficient mainly due to loss by excessive irrigation, percolation, and evapo-ration. Soilless culture may be an alternative to soil-based cultivation. Twohydroponic techniques, i.e., nutrient film technique and A-shaped aeroponicsand a closed insulated pallet system based on continuous subirrigationsystem with fertilizers in reservoirs to ensure a reserve within the root zone,were evaluated and compared to the conventional soil-based cultivationmethod (control) in Kuwait. The experiment was conducted in an acryliccovered greenhouse having an evaporative cooling system with ambienttemperatures ranging from 15 to 20°C at night and 24 to 35°C during the daythroughout the period from October 2005 to May 2006. Vegetative growth,flowering, and fruiting of bell pepper (Capsicum annuum L. cv. Yara) andstrawberry (Fragaria versca L. cv. Americana Porter) were evaluated.Yields were lower in the closed systems than for the control. There weresignificant differences between amounts of water consumed in the soillesstechniques with consumption ranging from 42.9 to 62.9% of the control for

M. Albaho (E-mail: [email protected]), B. Thomas (E-mail:[email protected]), and A. Christopher (E-mail: [email protected]) areaffiliated with Kuwait Institute for Scientific Research, P.O. Box 24885, 13109,Safat, Kuwait.

Address correspondence to M. Albaho at the above address.The authors thank the Kuwait Foundation for the Advancement of Sciences

for their sponsorship to this study.

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peppers and 54.3 to 79.1% for strawberry. CIPS was the most promisingsystem for adaptation for protected agriculture because of its simplicity,recyclability of most of its components, and water conservation efficiency.

KEYWORDS. Closed system, unconventional cultivation, vegetable crops

INTRODUCTION

Conventional soil-based cultivation systems are not water efficientmainly due to loss by excessive irrigation, percolation, and evaporation.A recent rise in the water table, coupled with increasing salinity, has beenreported in the majority of Kuwaiti farmlands as a consequence of use oftraditional soil-based production systems with prolonged excessive irriga-tion, lack of efficient drainage practices, and excessive fertilizer applica-tion. One approach to correct the problem is to adopt cultivation systemsthat are not dependent on soils. Soilless culture techniques will serve ascomplementary cultivation systems to provide a possible solution to theexisting problems of limited supply of high-quality water and minimizerisks associated with soil-based systems.

The difficulty and cost of controlling soil-borne diseases, soil salinity,lack of fertile soil, and shortages of good quality water have been majorreasons for the development of soilless substrates (Van Os et al., 2002).Over the last 20 years, soilless growing systems have become increasinglypopular among commercial growers since they improve quantity andquality of produce (Van Os et al., 2002). In comparison with conventionalground-bed cultivation in greenhouses, the nutrient film technique (NFT)resulted in earlier flowering, and higher flower yields, per plant withoutloss of quality and with considerable savings in the amount of water used incarnation production (Bowe and Reinelt, 1991). Benoit and Ceustermans(1991, 1993) suggested that considerable reduction in the crop durationand improvements in finished product quality in watercress (Rorippanasturtium-aquaticum L.) and chervil (Anthricus cerefolium L. Hoffmann)resulted when produced using the NFT system. The flexibility of the NFTsystem enabled it to be adopted for sweet pepper (Capsicum annuum L.),cucumber (Cumus sativus L.), lettuce (Lactuca sativa L.), leek(Allium ampeloprasum L. Porrum group), and spinach (Spinacia oleracea L.;Abou-Hadid et al., 1994a, 1994b; Al-Harbi, 1994; Kim et al., 1995; Bothet al., 1996; De Rijck et al., 1994; Motosugi et al., 1995).

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Soilless culture techniques will have far-reaching positive impacts onenvironmental health and sustainability of agriculture. These systemsare technically and economically viable and environmentally friendlyunder Kuwait’s conditions. The objective of this study was to evaluatethree greenhouse soilless techniques in comparison to the conventionalsoil-based cultivation method for growing bell pepper and strawberry(Fragaria versca L.) in Kuwait.

MATERIALS AND METHODS

The experiment was conducted in an acrylic covered greenhouse withan evaporative cooling system in which ambient temperatures rangedfrom 15 to 20°C at night and 24 to 35°C during the day from October2005 to May 2006.

On-ground Nutrient Film Technique (NFT)

The system consisted of precast open rectangular troughs that were14 m long, with a cross-sectional width and height of 22 and 15 cm,respectively (Figure 1). The troughs were covered with removable lids inwhich a single row of 8-cm-diameter holes, spaced 30 cm apart, weredrilled to accommodate plants. Each trough could hold 46 plants, and five

FIGURE 1. The nutrient film technique (NFT).

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troughs contained a total of 230 plants. The troughs were arranged inparallel on a gentle slope (<1%) facilitating the gravitational flow of thecirculating nutrient solution and were connected to the nutrient solutioninlet at the upper end. Each trough was equipped with an inflow meteringdevice. One set of alternating overhead pumps was used to deliver apremixed nutrient solution from a catchment tank to the inlet of thetrough. The nutrient solution, which forms a thin film flowing over theroots, was collected at the outlet and returned to the catchment tank bygravity flow for replenishment and then pumped back to plants.

A-shaped Aeroponics (AERO)

The apparatus (Figure 2) consisted of an A-shaped angular galvanizedstructure (14.65 m long) covered with expanded high-density polystyrenepanels on two sides (0.75 m long each). A misting system was pro-grammed to spray nutrient solution over the roots at 15-s·min−1 intervalsaround the clock. Excess nutrient solution was returned through a flowpipe to the catchment tank. The third side, which formed the base (1.05 mlong) of the A-shaped structure was laid open on high-density polythenesheets to collect the runoff nutrient solution for return to the catchmenttank. This system was connected to a dosing pump similar to that of theNFT. The structure as a whole was an on-ground model, placed on gentlysloping (<1% slope) even ground, which facilitated gravitational flow of

FIGURE 2. The A-shaped aeroponic system (AERO).

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runoff solution. The panels on both sides had a series of holes of 7.5-cmdiameter, which determines the planting density, to house seedlings raisedin rock wool cubes.

In the hydroponic systems (NFT and AERO), the fertilizer tank, con-taining concentrated fertilizer, had a capacity of 250 L and was connectedto the nutrient dosing device. The highly soluble fertilizer Kristalon®

(Fisons Horticulture, Doetinchem, The Netherlands), which contained18N-18P-18K-2Mg + trace elements, was used. The contents of the nutri-ent solution in the catchment tank are found in Table 1. Nutrient solutiontemperatures were maintained from 20 to 25°C.

Calcium, provided as Ca(NO3)2, was placed in a separate tank where anappropriate amount was periodically injected into the catchment tank througha fertilizer doser and mixed. EC and pH were maintained in the range of 1.9to 2.5 dS·m−1 and 5.6 to 6.5, respectively. The solution pH was adjusted byadding either phosphoric acid (500 mL; 85% orthophosphoric acid in 50 L ofwater) or sodium hydroxide (500 mL; 5N NaOH in 50 L of water).

CIPS

This is a continuous subirrigation-capillary system (Figure 3). Place-ment of fertilizer in conservers ensures the retention of a reserve withinthe root zone to increase availability to plants by ion diffusion and directroot contact (Albaho, 2006; Albaho and Al-Mazidi, 2005; Albaho and

TABLE 1. Composition of nutrient solution during experimentation period

Nutrient Element Concentrationrange (mg·L−1)

Nitrogen 175–200Phosphorus 30–40Potassium 350–400Calcium 175–200Magnesium 70–80Iron 10–12Manganese 0.7–1Boron 0.4–0.5Zinc 0.4–1Copper 0.2–0.3Molybdenum 0.01–0.1pH 5.0–6.0EC (mS/m) 1.9–2.3

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Green, 2004a, 2004b; Albaho and Green, 2000). Water reservoirs werefilled with about 495 L of desalinized irrigation water up to 2 cm belowthe bottom level of the basket (nursery pot cut in four sides). Basketswere suspended from the precut holes in the CIPS lid and supported bythe container-lip/lid overlap. Two capillary strips (10-cm wide) wereplaced across the bottom of baskets and extended downwards 30 cm tothe bottom of the reservoir. Copper hydroxide–treated cloth pouches werethoroughly soaked in water to permit easy diffusion of water across thepouch wall. The pouches were uniformly filled with the rooting medium(peat moss: perlite, 1:1 [v/v]) mixed with dolomite at 3.0 kg/m3 and gypsumat 1.8 kg/m3 and saturated with water to establish continuous capillarity.Thirty-seven grams of Kristalon and 15 g of calcium nitrate (Calcinit®,Hydro Agri [UK] Ltd., Immingham, UK) in separate polythene conserv-ers were placed in the rooting medium while filling. The pouches, plantedwith healthy seedlings, were placed in the baskets and the top exposedsurface of the rooting medium covered with two semicircular urethanecollars provided with a hole in the center to accommodate the plant stem.Surfaces of the polyurethane collars were sealed with reflective, heavy-duty aluminum foil to prevent evaporation loss of water. Space around thestem was filled with loose aggregates of polyurethane to minimize evapo-ration. Water level in the CIPS reservoir was monitored periodically andwater was added (and amounts recorded) when needed.

FIGURE 3. The closed insulated pallet system (CIPS).

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Soil Based System—Control (SOIL)

In this system, seedlings were planted in raised beds (approx. 50-cmwide) provided with a trickle irrigation system to facilitate fertigation.Each bed accommodated two rows of plants, spaced 40 cm apart.

Plant Materials

Sweet pepper, cv. Yara, and Strawberry, cv. Americana Porter, wereused. Seeds of sweet pepper were sown in 2.5-cm3 rock wool cubes.When seedlings were 14 days old, they were transferred to 7.5 cm3 rockwool cubes. All seedlings were fertilized with diluted Hoagland solution.The 7.5 cm3 rock wool cubes were transplanted into the NFT and AEROsystems when 30 days old. Seedlings of strawberries were purchasedfrom a local nursery and were immediately planted in the 7.5-cm3 rockwool cubes and fertilized with diluted Hoagland solution until they weretransferred to the NFT and AERO systems 30 days later.

Seedlings in 8-cm-diameter pots filled with peat moss and perlite mixin the ratio of 1:1 (v/v) were transplanted into the CIPS and seedlings in8-cm pots filled with peat moss, perlite, and sand in the ratio 1:1:1 (v/v/v)were transplanted into the soil, described later. Initial observations onplant height, canopy, number of leaves, chlorophyll index, and leaf areawere taken immediately after planting. Observations on vegetative growthparameters, i.e., plant height, number of leaves/plant, plant canopy size(displacement between farthest leaves in the canopy; in centimeters), andchlorophyll index were recorded at 20- and 10-day intervals in peppers andstrawberries, respectively. Date of first flowering, number of fruits/plants,and fruit yield were recorded during the reproductive growth stage.

Chlorophyll content index, a relative measure of chlorophyll value thatis proportional to the amount of chlorophyll in the sample, was determinedwith a CCM-200 chlorophyll content meter (Opti-Sciences, West Ford Rd.Ste # 4, Tyngsboro, Maine), which is a handheld, battery-operated instru-ment designed for rapid nondestructive determination of chlorophyllcontent in intact leaf samples. In addition, dry matter accumulation in theabove-ground portion was accumulated at 20-day intervals starting from40 days after transplant (DAT).

Experimental Design

The experiment was arranged in a simple, completely randomizedarrangement with production system being the single factor with 10 plants

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per each of four replicates. Analysis of variance was performed and treat-ment means were compared according to Fisher’s least significant differ-ence (LSD) procedures in SAS (ver. 8.1, SAS Inst., Cary, North Carolina). Datafor each crop were analyzed separately.

RESULTS AND DISCUSSION

Bell Pepper

Plant height (Figure 4), plant canopy (Figure 5), leaf area (Figure 6),and number of leaves (Figure 7) for plants grown in CIPS and SOILwere greater than for plants grown in hydroponics (NFT and AERO) atP ≤ 0.05. CIPS plants exhibited significantly greater chlorophyll indexthan those in the other systems beyond the 20 DAT (Figure 8).

FIGURE 4. Plant height over time of C. annuum, cv. Yara, grown withdifferent techniques. CIPS = closed insulated pallet system, AERO =aeroponics, NFT = nutrient film technique, and SOIL = soil-based cultivation,control. Lines around points on the graph represent standard error.

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FIGURE 5. Plant canopy size over time of C. annuum, cv. Yara, grown withdifferent techniques. CIPS = closed insulated pallet system, AERO =aeroponics, NFT = nutrient film technique, and SOIL = soil-based cultivation,control. Lines around points on the graph represent standard error.

FIGURE 6. Leaf area over time of C. annuum, cv. Yara, grown with differenttechniques. CIPS = closed insulated pallet system, AERO = aeroponics,NFT = nutrient film technique, and SOIL = soil-based cultivation, control.Lines around points on the graph represent standard error.

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FIGURE 7. Number of leaves over time of C. annuum, cv. Yara, grown withdifferent techniques. CIPS = closed insulated pallet system, AERO =aeroponics, NFT = nutrient film technique, and SOIL = soil-based cultivation,control. Lines around points on the graph represent standard error.

FIGURE 8. Chlorophyll index over time for C. annuum, cv. Yara, grown withdifferent techniques. CIPS = closed insulated pallet system, AERO =aeroponics, NFT = nutrient film technique and SOIL = soil-based cultivation,control. Lines around points on the graph represent standard error.

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Accumulated shoot dry matter in C. annuum was 65.3, 33.7, 24.3,and 45.4 g for CIPS, NFT, AERO, and SOIL, respectively, with anLSD0.05 = 15.2 g. C. annuum shoot dry matter content at 80 DAT wassignificantly higher in CIPS plants (36.8 g), followed by the SOIL (28.3 g)and NFT (26.3 g) plants. AERO was the lowest with only 18.3 g(LSD0.05 = 7.5g).

Flowering and fruiting was significantly earlier for plants under CIPSthan the other treatments (Table 2). NFT and AERO plants exhibited adelay in flower and fruit initiation. Mean fruit yield per plant for SOILplants from 60 to 120 DAT was greater than for all other treatments(Figure 9). That is, in CIPS, NFT, and AERO were 51.5, 32.2, and 26.7,respectively of that produced by SOIL plants.

All the closed production systems effectively reduced water con-sumption, with CIPS being the most efficient (Figure 10). Daily wateruptake per plant was highest in SOIL followed by NFT and AEROand then CIPS (Figure 10). Plants grown in CIPS, NFT, and AERO con-sumed 13, 19, and 20 L of water compared to 34 L for the SOIL treat-ment. The reduction of water requirements, i.e., percentage water savingover the control, were 62.9, 48.6, and 42.9% for CIPS, NFT, andAERO, respectively.

Strawberry

Plants in all treatments had satisfactory performance up to 30 DAT;the SOIL and AERO treatments were the most promising systems forstrawberries toward the end of this study. Maximum plant height

TABLE 2. Earliness in flower initiation and fruiting in bell pepper (C. annuum)

Production technique

Flower Initiation(DAT)z

Fruit Intitiation(DAT)z

AERO 37 43NFT 28 36SOIL (control) 20 25CIPS 16 21LSD0.05 7 8

zDAT = Days After Transplanting, CIPS = Closed Insulated PalletSystem, AERO = Aeroponics, NFT = Nutrient Film Technique andSOIL = soil-based cultivation, control.

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FIGURE 9. Mean fruit yield per plant over time for C. annuum, cv. Yara,grown with different techniques. CIPS=closed insulated pallet system,AERO=aeroponics, NFT=nutrient film technique, and SOIL=soil-basedcultivation, control. Lines around points on the graph represent standard error.

FIGURE 10. Mean daily water uptake per plant for C. annuum var. Yara,grown with different techniques. CIPS=closed insulated pallet system,AERO=aeroponics, NFT=nutrient film technique, and SOIL=soil-basedcultivation, control. Lines around points on the graph represent standard error.

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observed in NFT plants throughout the study was negatively corre-lated with the other vegetative attributes. It may be inferred that eti-olation, a result of shading of the crown portion in deep trays (15-cmdeep) was responsible for this result. Plants in the AERO systemexhibited superior performance throughout the experiment for mostparameters studied, and the values were comparable to control plants(SOIL).

Soilless systems as well as SOIL plants maintained steady progress ingrowth throughout the study, where mean plant heights reached theirmaxima at 80 DAT. Plant heights ranged between 18 and 24 cm in allproduction techniques. Plants in the AERO treatment had significantlygreater canopies (plant cover) than the other techniques, followed by theSOIL from 60 to 80 DAT (Figure 11). Plants grown in the AERO sys-tem maintained a significantly higher leaf area from 30 DAT until theend of the study followed by the other techniques. The NFT, CIPS, andSOIL plants had similar leaf area from 40 to 70 DAT. Plants in theSOIL treatment had a steep increase in leaf area accumulation in con-trast to a drastic drop in the AERO at 80 DAT (Figure 12). Significantly

FIGURE 11. Plant canopy size over time for strawberry (Fragaria versca L.var. Americana Porter) grown with different techniques. CIPS = closedinsulated pallet system, AERO = aeroponics, NFT = nutrient film technique,and SOIL = soil-based cultivation, control. Lines around points on the graphrepresent standard error.

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higher numbers of leaves were present on plants in the AERO treatment,followed by the CIPS up to 70 DAT. SOIL plants had the second high-est number of leaves at 80 DAT, but that number was significantlylower than the AERO plants (Figure 13). CIPS plants had a significantlygreater chlorophyll index than plants in the other systems after 10 DAT(Figure 14).

In spite of the significant delays in terms of flower and fruit initiationsof plants grown in SOIL compared to the soilless systems (Table 3), theSOIL had the maximum number of fruit and yield per plant followedby AERO plants (Figure 15). Strawberry plants grown on the NFT andCIPS ceased to produce at 80 DAT.

Significant water savings was obtained in CIPS compared to the control.Water uptake of strawberries was 60.4, 88.4, and 132.0 and 289 mL·d−1 inCIPS, NFT, AERO, and SOIL, respectively, with an LSD0.05 = 25.7 mL·d−1

(Figure 16). There was a water savings of 79.1, 69.4, and 54.3% overthe SOIL (control).

The production and delivery of fresh water to farms in Kuwait iscostly. Savings on irrigation water would be significant for sweet pepper

FIGURE 12. Leaf area over time for strawberry (Fragaria versca L. var.Americana Porter) grown with different techniques. CIPS = closedinsulated pallet system, AERO = aeroponics, NFT = nutrient filmtechnique, and SOIL = soil-based cultivation, control. Lines around pointson the graph represent standard error.

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and strawberry if some of the closed soilless systems were adopted.Adoption of these systems (especially CIPS) would eliminate saliniza-tion of soil and reduce water and fertilizer consumption. Althoughyields may be either comparable to, or less than, that of field production(especially in the cool season), water consumption is far less. Thisreduction of water use in this arid zone is beneficial where good-qualitywater is scarce and expensive.

CIPS is recommended as a potential growing system for vegetablesand small fruit due to its simplicity, high water use efficiency, recycla-bility of many of its components, requirements of low resource inputssuch as labor, and potential as an environmentally friendly technique.AERO can be suggested as a practical alternative for the conventionalsoil culture of strawberry due to water and soil conservation. However,the system demands costly inputs in terms of uninterrupted electricpower and technical know-how. Desalinized irrigation water is expen-sive and adds to the cost of greenhouse production, but generally pro-ductivity is considerably higher than field production and the amount of

FIGURE 13. Number of leaves over time for strawberry (Fragaria verscaL. var. Americana Porter) grown with different techniques. CIPS = closedinsulated pallet system, AERO = aeroponics, NFT = nutrient filmtechnique, and SOIL = soil-based cultivation, control. Lines around pointson the graph represent standard error.

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water needed is much less. With soilless culture the possibility exists tominimize water consumption for high cash crops in protected agricul-ture and utilization of protected systems can complement field cultiva-tion in this arid part of the world.

FIGURE 14. Chlorophyll index over time for strawberry (Fragaria versca L.var. Americana Porter) grown with different techniques. CIPS = closedinsulated pallet system, AERO = aeroponics, NFT = nutrient filmtechnique, and SOIL = soil-based cultivation, control. Lines around pointson the graph represent standard error.

TABLE 3. Earliness in flower initiation and fruiting in strawberries

Production technique

Flower Initiation(DAT)z

Fruit Intitiation(DAT)z

SOIL 20 31AERO 16 26CIPS 14 25NFT 14 24LSD0.05 2.6 3.1

zDAT = Days After Transplanting, CIPS = Closed Insulated Pal-let System, AERO = Aeroponics, NFT = Nutrient Film Techniqueand SOIL = soil-based cultivation, control.

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FIGURE 15. Mean fruit yield per plant for strawberry (Fragaria versca L.var. Americana Porter), grown with different techniques. CIPS = closedinsulated pallet system, AERO = aeroponics, NFT = nutrient filmtechnique, and SOIL = soil-based cultivation, control. Lines around pointson the graph represent standard error.

FIGURE 16. Mean daily water uptake per plant for strawberry (Fragariaversca L. var. Americana Porter), grown with different techniques. CIPS =closed insulated pallet system, AERO = aeroponics, NFT = nutrient filmtechnique, and SOIL = soil-based cultivation, control. Lines around pointson the graph represent standard error.

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