performance of wick irrigation system using self-compensating benches with substrates for lettuce...

Performance of wick irrigation system using self-compensating troughs with substrates

for lettuce production

Rhuanito Soranz Ferrarezi* and Roberto Testezlaf

School of Agricultural Engineering, University of Campinas, Campinas, São Paulo, Brazil.

We thank Dr. Flávio Bussmeyer Arruda, Antonio Carlos Ferreira Filho, Maurício Madoglio

Sultani, Renato Traldi Salgado and Vicente Dias Martarello for technical collaboration, Dr.

Marc van Iersel for review of the manuscript and constructive criticism, the School of

Agricultural Engineering for donating the material for the assembly of the experimental plots,

the Hidrogood Horticultura Moderna Company for donating the self-compensating troughs,

and the National Council of Technological and Scientific Development (Ministry of Science

and Technology, Brazil) for a PhD scholarship to the first author. Funding for this research

was provided through the PRP/FAEPEX/UNICAMP (award no 261/10).

The authors declare that the mention of a trademark, proprietary product, or vendor does not

constitute a guarantee or warranty of the product and does not imply its approval to the

exclusion of other products or vendors that might also be suitable.

* Address correspondence to: 501 Cândido Rondon Avenue, 13083-875, Campinas, São

Paulo, Brazil. Email address: [email protected]

mailto:[email protected]

Performance of wick irrigation system using self-compensating troughs with substrates 1

for lettuce production 2

3

Abstract 4

Subirrigation systems in which water and nutrients are supplied to the substrate through wick 5

strips for upward nutrient solution (NS) movement can be a feasible alternative to improve 6

lettuce quality with low environmental pollution, enabling production with reduced labor and 7

electricity or in regions with high air temperature. The objective of this study was to compare 8

the performance of two wick irrigation system using self-compensating troughs filled with 9

either pine bark (WPB) or coconut coir (WCC) with nutrient film technique (NFT) 10

hydroponic system for greenhouse lettuce production. The daily monitoring of electrical 11

conductivity (EC) and pH allowed the management according to the recommended values for 12

optimal lettuce growth. The EC showed variation among troughs and salt accumulation in 13

substrates, with WPB exhibiting two-fold greater EC than WCC (ranging from 0.95 to 7.57 14

and from 0.68 to 3.67 dS∙m-1, respectively), while the pH values were stable over time. WCC 15

promoted greater root length and shoot diameter, while WPB produced shorter plants 16

compared to the other two treatments. NFT resulted in an 83% lower leaf area and 44% lower 17

root volume than WPB and WCC. The fresh and dry shoot masses with NFT were 58% and 18

24% lower than with WPB and WCC, respectively. The fresh root mass was also reduced in 19

NFT plants, which was 67% smaller than WCC and 59% smaller than WPB. Root dry mass 20

of NFT was 35% lower than the average of WPB and WCC. NO3-N, NH4-N, P, K, Ca, Mg, 21

S, B, Cu, Fe, Mn and Zn concentration in plant shoot and root at the end of the experiment as 22

well as the same nutrients, chloride, sodium and bicarbonate concentrations in substrate and 23

NS determined weekly differed among the treatments (P < 0.01). The EC and nutrient 24

concentration in the substrates increased over time. The wick irrigation system had higher 25

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productivity with both substrates than NFT, with higher yield and plant quality in WCC, 26

indicating its feasibility as an alternative greenhouse lettuce production system. However, 27

due to the salinity buildup, water and nutrition management needs to be optimized for self-28

compensating troughs to avoid an increase in substrate EC over time. 29

Keywords. Subirrigation, Hydroponics, Nutrient concentration, Lactuca sativa L. ‘Vanda’, 30

Greenhouse, NFT. 31

32

Introduction 33

Lettuce (Lactuca sativa L.) is the most consumed salad vegetable in Brazil (Santos et 34

al., 2010), representing 50% of all leafy vegetables commercialized in the food supply 35

distribution centers in the country (Moretti and Mattos, 2008). Currently, lettuce is grown 36

both in soil and hydroponic systems. In soil, the cultivation occurs in raised beds, where 37

plants are subjected to weather changes, which can result in plant yield and quality reduction 38

(Feltrim et al., 2009). Furthermore, consecutive years of crop production promotes the 39

contamination of soil and groundwater with nutrients and pesticides. The most used 40

hydroponics system in lettuce production is the nutrient film technique or NFT (Cometti et 41

al., 2008 and Feltrim et al., 2009). 42

NFT hydroponics promotes higher efficient use of greenhouse area and higher yield 43

(Santos et al., 2010), with better crop quality (Lopes et al., 2007 and Santos et al., 2010) and 44

shortened crop cycles due to better environmental control (Martins et al., 2009 and Santos et 45

al., 2010), allowing year-round cultivation and harvesting (Helbel Junior et al., 2008). The 46

advantages also include higher water and fertilizer use efficiency, with the possibility of NS 47

reuse, resulting in environmental preservation by reducing fertilizer and pesticide deposits in 48

soils and groundwater contamination (Martins et al., 2009 and Santos et al., 2010), and 49

reduced labor during crop production (Martins et al., 2009). However, hydroponics presents 50

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challenges for growers, as dependence on electric power for NS circulation and aeration, with 51

the risk of losing the entire production if a prolonged power outage occurs (Silva et al., 52

2005), and difficulty of adoption in regions with high air temperature due to high temperature 53

of the NS, which complicates plant establishment and management (Alberoni, 1998). The 54

requirement of technical knowledge and permanent technical support and the possibility of 55

pathogen dissemination due to NS recirculation are also major concerns (Resh, 2002). 56

To improve crop quality and reduce environmental pollution, new production systems 57

are being developed to enable lettuce cultivation with limited manpower and electricity, or in 58

regions with high air temperature. Subirrigation systems, in which water and nutrients are 59

supplied to the substrate through capillary action (Caron et al., 2005) and hydraulic 60

redistribution (Prieto et al., 2012) can be viable alternatives. 61

A wick irrigation system operates in a closed cycle, without runoff, permitting 62

appropriate plant nutrition and creating alternatives to improve production uniformity. These 63

systems show major advantages: 1) independence of electricity for operation (Andriolo et al., 64

2004); 2) high water and nutrient use efficiency (Son et al., 2006); 3) less need for 65

manpower, as the management is simplified compared with conventional cultivation, 66

providing cost reduction (Andriolo et al., 2004); 4) increase in the uniformity and quality of 67

production (Oh and Son, 2008); 5) water use savings (Laviola et al., 2007); and 6) 68

temperature control of the root system (Laviola et al., 2007). Wick irrigation systems can be 69

used for the cultivation of ornamental plants, such as chrysanthemums and poinsettias (Kang 70

et al., 2009), kalanchoe (Lee et al., 2010) and cyclamen (Oh and Son, 2008). Ferrarezi et al. 71

(2012) suggested that wick irrigation systems might be used in the production of vegetables 72

or condiment and aromatic plants. 73

Several studies using the wick irrigation system were performed with different 74

equipment for many crops and environmental conditions. The results from these studies 75

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revealed the optimum wick width and suitable water depth for wick contact (Kang et al., 76

2009), the wick length to improve water distribution (Lee et al., 2010 and Son et al., 2001), 77

the possibility of covering the substrate surface to reduce evaporation (Son et al., 2006), the 78

suitable size of the growing container (Lee et al., 2010), the substrate composition for 79

satisfactory root wetting and moisture maintenance (Lee et al., 2010 and Oh et al., 2007), the 80

possibility of disease incidence and spread (Lee et al., 2010 and Oh and Son, 2008), and 81

efficiency equipment use (Laviola et al., 2007). 82

At the present time, the Brazilian market only has one commercial wick system 83

available, called self-compensating troughs. This wick irrigation system was evaluated by 84

Ferrarezi et al. (2012), showing that the equipment had some imperfections in the lower 85

reservoir for NS storage, determining significant differences among the water depth, time and 86

filling volume, and uniformity of water distribution (UWD) in two commercial substrate 87

(pine bark and coconut coir, same systems used at this experiment). They found higher 88

moisture and UWD in pine bark. According to Andriolo et al. (2004), the use of substrates 89

allowed the reduction of approximately 92.4% of pump operation time compared with NFT, 90

simplifying both fertigation management and NS control. However, studies evaluating the 91

performance of the wick irrigation system for lettuce production using different substrates for 92

cultivation in Brazil remain scarce. The hypothesis of this research is that wick irrigation 93

system promotes higher lettuce production compared to NFT in greenhouses. 94

Thus, the objective of this study was to compare the performance of two wick 95

irrigation system using self-compensating troughs filled with either pine bark or coconut coir 96

with NFT for lettuce production in a greenhouse. This technical information can support 97

decision-making situations when wick or NFT systems are appropriate. 98

99

Material and Methods 100

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Location. The experiment was performed at the School of Agricultural Engineering 101

(FEAGRI), University of Campinas (UNICAMP), in Campinas, SP, Brazil, from June 22 to 102

July 20, 2010. Experimental plots were assembled in a Venlo-type greenhouse, covered with 103

150 μm-thick agricultural polyethylene film, with 18.2 x 6.4 x 3 m (length x wide x ceiling), 104

without roof vents, with a frontal and side 0.87 x 0.30 mm anti-aphid screen and a 40-cm 105

masonry bottom. 106

107

Plant material. Seedlings of lettuce ‘Vanda’ (Sakata Seeds, Bragança Paulista, SP, Brazil) 108

grown in Styrofoam trays with coconut coir substrate for 28 days were purchased from a 109

nursery (Selma Mudas, Bragança Paulista, SP, Brazil), and transplanted into the experimental 110

plots on June 18, 2010, and irrigated daily to ensure proper plant rooting. 111

112

Water and NS. Water was from the municipal system and had the following chemical 113

characteristics: pH = 7.1, EC = 0.2 dS∙m-1 and nutrients (mg∙L-1): NO3-N = 2.3, NH4-N = 0.4, 114

P = 1.5, K = 14.8, Ca = 13, Mg = 2.1, S = 1.7, B = 0.1, Cu = <0.01, Fe = 0.1, Mn = 0.02, Zn 115

= 0.01, chloride = 23.4, sodium = 12.3 and bicarbonate = 100.4. 116

The NS used throughout the experimental period was prepared using 3 mL∙L-1 of 117

FloriSol Veg (Conplant Ferti, Campinas, SP, Brazil) and 0.3 g∙L-1 of magnesium sulfate 118

(Produquímica, Suzano, SP, Brazil), with pH = 4.24, EC = 1.8 dS∙m-1 and the nutrient 119

concentrations (mg∙L-1): total-N = 198 (NO3-N = 174 and NH4-N = 24), P = 31, K = 187, Ca 120

= 143, Mg = 60, S = 36, B = 0.5, Cu = 0.5, Fe = 1.8, Mn = 0.5, Mo = 0.1, Ni = 0.1 and Zn = 121

0.2. The pH was kept between 5.5 to 6.5 using H3PO4 or KOH 1 N solution to maintain the 122

chelates in a stable form (Ferrarezi et al., 2007), with the daily replenishment criteria of 123

Furlani et al. (1999) and weekly replacement to avoid nutrient concentration fluctuations. 124

125

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Treatments and substrates. We evaluated three treatments: a wick irrigation system with 126

coconut coir substrate (WCC), a wick irrigation system with pine bark substrate (WPB), and 127

a nutrient film technique hydroponics system (NFT). The substrates used were coconut coir 128

Golden Grain Mix (Amafibra, Ananindeua, PA, Brazil) and pine bark Citrus 9 (Mec Plant, 129

Telêmaco Borba, PR, Brazil). Both substrates were analyzed prior to transplanting for macro 130

and micronutrient determination at the Substrate Analysis Laboratory (Instituto Agronômico 131

de Campinas, Campinas, SP, Brazil) using Sonneveld and van Elderen (1994) extraction 132

method (Table 1). 133

134

Wick irrigation system. The troughs for wick irrigation were made out of polypropylene and 135

were resistant to chemical action. The equipment consisted of two compartments: a lower 136

reservoir for NS storage (bottom) and a substrate deposition chamber (top), which were 137

interconnected by a wick strip of synthetic non-woven mat (SNWM) (Figure 1). This wick 138

conducted NS from the bottom to the top compartment, moistening the substrate and 139

supplying water and minerals to plants (Ferrarezi et al., 2012). 140

The complete wick irrigation system consisted of a 50 L-tank (Puma Tambores, 141

Piracicaba, SP, Brazil), 32 mm water supply hose (Tramontina, Recife, PE, Brazil), 2 L-142

micro reservoir and five self-compensating troughs (Hidrogood Horticultura Moderna, 143

Taboão da Serra, SP, Brazil) per experimental plot (Figure 2). These 0.175 x 4.0 x 0.7 m 144

(width x length x height) troughs were recommended for leafy vegetables production and had 145

a 26-L capacity in the substrate deposition chamber and 9-L in the lower reservoir for NS 146

storage. The micro reservoir had a mini float that regulated the solution flow from the tank 147

connected to the lower reservoir through polyvinyl chloride (PVC) pipes. The system supply 148

with NS was mediated by gravity, requiring leveled installation of troughs and micro 149

reservoir. As the plant absorbed water and nutrients from the substrate, the wick 150

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automatically replenished the solution. Thus, the plant regulated the solution flow to the 151

substrate by the difference in total potential and capillary action, without requiring automated 152

controls, pumps, emitters, etc (Ferrarezi et al., 2012). One plot with five troughs was 153

assembled for each wick treatment tested (one with coconut coir and another with pine bark 154

substrate). The countertop was 1.2 x 4.0 m (width x length) and completely leveled. The 155

seedlings were spaced every 0.25 m, totaling 15-16 plants per trough. 156

157

NFT hydroponic system. The NFT system was composed of an underground 250 L-tank 158

(Acqualimp, Valinhos, SP, Brazil), an 0.85 HP irrigation pump (Hydrobloc C800T, KSB, 159

Várzea Paulista, SP, Brazil), timer (MT-2001, Didziel, São Paulo, SP, Brazil), 32 mm-water 160

supply pipe (Tigre, Joinville, SC, Brazil), five 90 mm x 4 m (width x length) trapezoidal 161

hydroponic channels (Hidrogood Horticultura Moderna, Taboão da Serra, SP, Brazil) and 75 162

mm-drain pipe (Tigre, Joinville, SC, Brazil). The countertop was 1.2 x 4.0 m (width x 163

length), with a 6% slope to allow NS return to the tank and a 1 L∙min-1 flow rate per channel, 164

both recommended by Furlani et al. (1999) for Brazilian conditions. The seedlings were 165

spaced every 0.25 m, totaling 15-16 plants per channel. During the first 10 days of the 166

experiment, a timer activated the pump for 5 min at 15-min intervals from 7 am to 5 pm due 167

to the small plant size. From day after transplant (DAT) 11 until the end of the experiment, 168

the pump was turned on continuously from 7 am until 5 pm because lettuce grown in high 169

temperature regions require a continuous supply of NS (Graves, 1983 and Graves and Hurd, 170

1983) or intervals of up to 5 min to promote adequate plant watering and nutrition (Zanella et 171

al., 2008). From 5 pm to 7 am, the system was irrigated for 5 min every 2 h. 172

173

Parameters evaluated. The temperature and relative humidity inside the greenhouse were 174

monitored every 5 min using a digital thermo-hygrometer (HT-4000, ICEL, Manaus, AM, 175

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Brazil) mounted at the same height as the self-compensating troughs (0.7 m above the soil 176

surface). All recordings throughout the experimental period were stored in a data logger. 177

The EC and pH in the substrates and in the NS from NFT and wick tanks were daily 178

monitored. For the substrates, we used an adaptation of the 1:1.5 Dutch extraction method 179

from Sonneveld and van Elderen (1994): removal of 100 mL sample from each substrate, 180

addition of 150 mL of tap water, stirring for 30 minutes and standing for 30 minutes. For the 181

tanks NS analyses, a sample from the NFT treatment was withdrawn from each channel, and 182

a sample from each wick irrigation system was directly collected from each tank. The 183

solutions were then transferred to individual test tubes, and EC and pH readings were taken 184

(DM-31 conductivity meter and a DM-21 pH meter, Digimed, São Paulo, SP, Brazil). When 185

the substrate EC reached values higher than double recommended for lettuce production, 186

equals to 4 dS∙m-1 in the average of the three troughs, we added only tap water in the WPB 187

and WCC tanks or leached all the substrate in the troughs with tap water, to avoid plant 188

damage caused by salt excess. Tap water applications to replace NS occurred on DAT 7, 10 189

and 14 in WPB and day 14 in WCC. Substrate leaching was performed on DAT 9 and 12 190

only in WPB. 191

The biometric parameters – root length, shoot diameter and height, root volume 192

(determined through water volume displacement in a graduated cylinder, according to 193

Sant’ana et al., 2003), number of leaves, and leaf area of all experimental plants (determined 194

using a Li-Cor 3100 leaf area meter, from Li-Cor, Lincoln, Nebraska, USA) – were taken at 195

DAT 28. The plants were then separated into shoots (leaves + stems) and roots for shoot 196

(SFM) and root (RFM) fresh mass determination. This material was dried in an 85 °C oven 197

with forced circulation (MA 037, Marconi Equipamentos de Laboratório Ltda, Piracicaba, 198

SP, Brazil) to obtain shoot (SDM) and root (RDM) dry mass. The plant yield based on fresh 199

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and dry mass was expressed per unit area. The leaf water content was calculated as [(SFM - 200

SDM) / SFM] x 100%. 201

Chemical analysis of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn and Zn were performed at 202

harvest in shoot and root, substrate and NS samples at the Soil, Plant and Substrate Analysis 203

Laboratory (Instituto Agronômico de Campinas, Campinas, SP, Brazil). For shoot and root 204

we used the method described by Bataglia et al. (1983) in three plants per replication from 205

the same samples used for the fresh and dry mass determination. For substrate we used the N 206

steam distillation method indicated by Cantarella and Trivelin (2001) and inductively coupled 207

plasma optical emission spectrometry (ICP-OES) for the other nutrients. Three substrate 208

samples per replication were collected weekly, with solution extraction being performed 209

according to the 1:1.5 Dutch method (Sonneveld and van Elderen, 1994). We used the same 210

method for NS, plus chloride determination by ion-selective electrode, sodium using 211

photometry, and bicarbonate through potentiometric titration, in samples collected weekly 212

after water replenishment and before the weekly replacement. 213

214

Experimental design and statistical analysis. The experimental design was a completely 215

randomized block, with three treatments and three replications. Twelve plants were harvested 216

from the center three troughs/channels for the biometric analysis, totaling 36 plants per 217

treatment. All results were tested using the Shapiro-Wilk normality test and transformed 218

adequately when necessary. The biometric parameters, plant yield, shoot:root ratio, leaf water 219

content and tissue nutrient concentration data (shoot and root) were subjected to analysis of 220

variance and Tukey’s mean separation (SAS 9.2, SAS Institute, Cary, NC). Over time 221

changes in nutrient concentration in the NS and substrates were analyzed by regression 222

models (Sigma Plot 11, Jandel Scientific, Corte Madera, CA). The results were considered 223

significant when P < 0.05. 224

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225

Results and Discussion 226

Climatic parameters 227

The high temperature in the greenhouse varied between 45 to 50 °C from DAT 1 to 228

16, and then decreased due to weather conditions (Figure 3), exceeding the optimum range of 229

15-25 °C recommended by Helbel Junior et al. (2008), Santos et al. (2009), and Martinez 230

(2006) for lettuce. There was a decrease in temperature and an increase in relative humidity 231

in the final third of experimental period, because of cooler weather. 232

We detected a negative effect of the temperature in the NFT treatment, producing 233

smaller plants than the substrate treatments, as a consequence of the air (Figure 3) and the NS 234

temperature. The averaged weekly temperature of the NS in the NFT tank was 32 °C, and in 235

wick irrigation system tanks was 28 °C (data not shown). All temperatures exceeded the 236

range of 18-24 °C for summer and 10-16 °C for winter recommended by Alberoni (1998) to 237

maintain a higher oxygen concentration for root respiration and metabolic reactions in the 238

roots (Helbel Junior et al., 2008). López-Pozos et al. (2011) indicated that low oxygenation in 239

recirculating hydroponics induces root hypoxia as a result of low oxygen solubility, 240

especially in warm climates, reducing crop yield. According to Santos et al. (2009), high 241

temperatures of NS can negatively influence lettuce plant architecture, weight, quality, and 242

yield. Our greenhouse did not provide any temperature control and the frontal side was built 243

with an anti-aphid screen, which reduced the air movement and can contributed to heating. 244

We used this screen because this greenhouse was set up for citrus seedling production, 245

following the vegetable sanitary protection guidelines and plant protection conformity 246

certification for citrus seedlings production in São Paulo State (Coordenadoria de Defesa 247

Agropecuária do Estado de São Paulo, 2005). One of the reasons for the high NS 248

temperatures could be the pump overheating due to its over sizing for the small dimensions of 249

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the experimental plot and the metal pump casing which warmed the solution during 250

continuous pumping. 251

252

Daily monitoring of the EC and pH 253

The EC varied among the troughs throughout the experimental period as a result of 254

salt accumulation in the WPB and WCC substrates (Figure 4). In WPB, EC was more than 255

twice than that in WCC (ranged from 0.95 to 7.57 and from 0.68 to 3.67 dS∙m-1, 256

respectively), perhaps due to the increased evaporation from the growing media as compared 257

with WCC (Lopes et al., 2007). These EC values were higher than recommended for lettuce 258

by Furlani et al. (1999) (1.6 to 1.8 dS∙m-1) and Castellane and Araújo (1995) (up to 2.5 dS∙ 259

m-1). This increase in EC was faster at the beginning of the experiment (DAT 7) because the 260

plants did not fully cover the substrate surface, thus increasing evaporation. However, EC 261

also increased in the middle of the experiment in WCC (DAT 13). The salt accumulation in 262

WPB induced typical edge-burn symptoms in older leaves due to salt excess. 263

When plants are subirrigated, an increase in the EC at the upper substrate layer is 264

frequently observed due to the evaporation and salt concentration (Dole et al., 1994; Argo 265

and Biernbaum, 1995; Rouphael and Colla, 2005; and Rouphael et al., 2006). Santos et al. 266

(2010) showed that high EC can reduce the number of lettuce leaves, stem diameter, shoot 267

fresh and dry mass, and water content. 268

The most common management strategies used to reduce EC include the use of NS 269

with lower EC, periodic substrate leaching, or addition of tap water to the tanks. We used the 270

last two strategies to reduce the EC of the substrate when it increased over the recommended. 271

We leached the substrates on DAT 8 and 11, and used tap water instead of NS on DAT 7, 11, 272

and 14, effectively reducing the concentration of all nutrients in WPB, with a consequent 273

reduction in pH and EC (Figure 4). Therefore, the EC of the NS was close to zero twice in 274

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WPB and once in WCC (Figure 4), allowing the EC reduction in the substrate and plant 275

growth recovery. However, this substrate EC subsequently increased again, which could be a 276

challenge to growers due to the constant requirement of monitoring and management of EC 277

to avoid plant damage (Figure 4). Furthermore, this procedure was time consuming, resulting 278

in significant volumes of water wasted to the environment due to disposal of the NS in the 279

greenhouse soil, which can be the major limitation of the wick irrigation system. In addition, 280

the use of tap water in substrate-grown crops may introduces bicarbonates at high 281

concentrations depending also on the bicarbonate concentration in the irrigation water which 282

in most cases is excessively high, thereby resulting in too high pH levels in the root zone, 283

being an undesired impact. In the present study, the bicarbonate concentration in the 284

irrigation water was not very high. 285

The pH of the NS showed spikes in the WPB treatment due to the use of tap water in 286

the tank for substrate leaching to reduce EC in the self-compensating troughs (Figure 4, 287

WPB). In addition, the pH of the NS in the WCC treatment was higher than WPB during the 288

entire production cycle, and spiked when tap water was added to the tanks (Figure 4, WCC). 289

Measurements in the NFT treatments were relatively consistent throughout the experimental 290

period, as a result of using the same NS in all channels (Figure 4, NFT). 291

292

Biometric parameters 293

At harvest, the WCC treatment resulted in 13% longer roots than WPB and 61% 294

longer than NFT (Table 2, P < 0.0001). Those were similar to the results of Silva et al. 295

(2005). But NFT was approximately one-third lower than the other two substrates. A similar 296

effect was observed with shoot diameter in WCC, which was 6% larger than WPB and 27% 297

larger than with NFT (Table 2, P < 0.0001). The shoot diameter responses for WPB and 298

WCC were similar to those observed by Santos et al. (2010), and higher than reported by 299

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Feltrim et al. (2009) and Helbel Junior et al. (2008). However, NFT plants had smaller shoot 300

diameter than that observed by either of these authors. The WPB treatment had shorter plants 301

than the other two treatments (Table 2, P = 0.0069). 302

The plants from the NFT treatment produced 83% less root volume and 44% smaller 303

leaf area than the average of the WPB and WCC treatments (Table 2, P < 0.0001). These 304

results differ from those of Silva et al. (2005), who found no difference for these variables 305

between the hydroponic and the capillary wick system. Root volume and leaf area (Table 2, P 306

< 0.0001) were higher than those found by Silva et al. (2005), who also used wick irrigation, 307

similar to those obtained by Santos et al. (2010) for ‘Vera’. But our results were 50% lower 308

than those of Feltrim et al. (2009) and Zanella et al. (2008), most likely due to the shorter 309

crop cycle (28 days) in our experiment. The number of leaves did not differ among the 310

treatments (Table 2, P > 0.05). 311

The NFT treatment produced plants with 58% and 24% lower SFM and SDM, 312

respectively, than with both substrates (Table 2, P < 0.0001). Comparing these results with 313

other studies using hydroponics, the SFM in NFT (54.1 g∙plant-1) was similar to the reported 314

by Santos et al. (2010) (58 g∙plant-1) and lower than Feltrim et al. (2009) (338.99 g∙plant-1) 315

and Helbel Junior et al. (2008) (413.4 g∙plant-1). In WPB and WCC substrates (≈130 g∙ 316

plant-1), SFM was three times higher than observed by Silva et al. (2005) (≈40 g∙plant-1). The 317

SDM treatments grown in substrates was two times higher than that observed in Martins et al. 318

(2009) (equal to 5.68 g plant-1 at 30 days after transplanting), and five times greater than 319

Silva et al. (2005); notably, similar results were reported by Cometti et al. (2008) and Zanella 320

et al. (2008). 321

RFM was also reduced in NFT treatment, which was 67% lower than WCC and 59% 322

lower than WPB (Table 2, P < 0.0001). The RDM of NFT-treated plants were 35% lower 323

than the average of WPB and WCC (Table 2, P < 0.0001). Probably the high temperatures 324

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inside the greenhouse and from the NFT NS might have accelerated the lettuce cultivation 325

cycle, resulting in smaller plants than observed in other studies using this crop (Helbel Junior 326

et al., 2008). 327

The lettuce yields in WPB and WCC treatments did not differ statistically, but were 328

60% and 30% higher, than in NFT on a fresh and dry basis, respectively (Table 3, P < 329

0.0001). Comparing with other studies, ‘Vanda’ lettuce yield in the present study were lower 330

than those for ‘Isabella’ (5.12 kg∙m-2, Martins et al., 2009) and ‘Veronica’ (5.77 kg∙m-2, 331

Faquin et al., 1996), but higher than the yield obtained with the conventional soil system (1.1 332

kg∙m-2, Grangeiro et al., 2006). The yield for treatments with WPB (3.844 kg∙m-2) and WCC 333

(4.078 kg∙m-2) were higher in this study than for the cultivars ‘Marisa’, ‘Verônica’, ‘Veneza 334

Roxa’ and ‘Vera’ used by Feltrim et al. (2009) (3.29 kg∙m-2) and ‘Regina’ and ‘Mimosa’ by 335

Andriolo et al. (2004) (3.1 kg∙m-2), both using pine bark substrate, because of the growth 336

reduction caused by high temperatures in summer time. 337

The shoot:root ratio differed among treatments, with WPB having the lowest values 338

(Table 3, P = 0.0147). These results were similar to those obtained by Santos et al. (2010). 339

The leaf water content was comparable to that reported by Santos et al. (2010), which was 340

about 8% lower in WCC compared with other growing medias (Table 3, P < 0.0001). 341

The NFT induced the lowest root length, shoot diameter and height, root volume, leaf 342

area, shoot (SFM) and root (RFM) fresh mass and shoot (SDM), root (RDM) dry mass (Table 343

2) and lower plant yield (Table 3) at harvest compared with the lettuce grown in substrate, 344

probably because of the high temperature of the NS in contact with plant roots. Conversely, 345

the lettuce grew exuberantly in the WPB and WCC treatments (Table 3), showing salability 346

and higher quality than NFT. Probably both substrates provided an increase in the oxygen 347

concentration at the root system due to the porous space between particles, reducing the 348

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negative effects of the high NS temperatures. Unfortunately this study measured neither the 349

temperature nor the oxygen content in the NS. 350

351

Shoot and root macro and micronutrient concentrations 352

There were no visual symptoms of nutrient toxicity or deficiency in plants throughout 353

the experimental period, except for the salt accumulation in WPB, which induced typical 354

edge-burn symptoms in older leaves, probably caused by high EC in this substrate at the 355

beginning of experiment. 356

The shoot macronutrient analysis indicated that N, Ca and Mg concentrations were 357

higher in the WPB treatment and that P and K concentrations were lower in NFT compared 358

with other substrates (Table 4). The S concentration was 35% higher in NFT compared with 359

WPB and WCC. These values were similar to those observed by Martins et al. (2009) and 360

Lopes et al. (2007) and were consistent with the values recommended by Silva (1999) and 361

Trani and Raij (1997), with the exception of Ca, which was slightly below the recommended 362

range (15 to 25 g∙kg-1). The shoot macronutrient concentrations were lower in NFT compared 363

with the plants grown in wick substrates, probably due to the lower growth caused by the 364

temperature of the NS (Table 4). Helbel Junior et al. (2008) cited that high NS temperatures 365

can induce plant root damage, causing reduction in the nutrients uptake and consequently in 366

the growth because of feed deficiency. 367

An analysis of the shoot micronutrient concentrations in lettuce revealed that WPB 368

resulted in a B concentration that was 29% lower than in the other treatments (Table 4). The 369

Cu concentration in the NFT treatment was 11.2 times greater than WPB and 5.5 times 370

greater than WCC, and the Zn concentration was 4.2 times higher in the NFT than the other 371

substrates. The WCC treatment showed the highest values for Fe, which was 39% higher than 372

WPB and 24% than NFT (Table 4). There was no significant difference among substrates for 373

of 24

the shoot Mn concentration. The results were consistent with those indicated by Silva (1999) 374

and Trani and Raij (1997). However, the Cu and Zn values were higher than the optimal level 375

indicated by these authors. 376

The root macronutrient concentrations were 73% higher for N, 82% for P, 60% for K 377

and 70% for S in NFT compared with substrates (Table 4). However, the Ca and Mg 378

concentrations were 41% and 58% higher, respectively, in WPB than in other treatments 379

(Table 4). 380

The root micronutrient concentrations with NFT were higher for B (2 times higher), 381

Cu (153 times higher), Fe (2 times higher) and Zn (31 times higher) than with the other 382

substrates (Table 4). This result was most likely due to the incomplete removal of these 383

elements during the substrate washing procedures in the lab, accumulating more nutrients in 384

the roots due to the direct contact with NS. In contrast, lettuce roots grown with NFT had the 385

lowest Mn concentration, with 28% higher values in WCC and 48% higher in WPB (Table 386

4). 387

The results on nutrient concentrations in the plant tissues were not only associated 388

with technical characteristics of the tested wick systems and concomitant plant physiological 389

implications, but also rather to differences in the nutrient supplied in each treatment. We 390

applied tap irrigation water several times in the wick irrigation system, which had a quite 391

different composition than the NS, in order to leach out salts as recommended by the 392

manufacturer, while in the NFT system we only applied NS. Thus, the performance of the 393

wick irrigation treatments could have been biased by operations that were not inherent to the 394

system, but had to be performed to reduce substrate EC. The frequency of tap water 395

application still unknown by growers. 396

397

Substrate macro and micronutrient concentrations 398

of 24

The macronutrient concentrations differed between the two substrates (Figure 5). 399

Compared to the initial nutrient levels in the substrates (Table 1), all nutrients increased with 400

nutrient solution supply, while pH decreased due to the acidifying characteristic of the used 401

NS. In general, pH, EC, NO3-N, Ca, Mg, and S were higher in WPB, while NH4-N, P, and K 402

were higher in WCC (Figure 5). 403

Substrate concentrations of Mn and chloride were higher in WPB, while B, Cu, Fe, Zn 404

and sodium were higher in WCC (Figure 5). There was a quadratic pattern of B, Fe and Zn 405

concentrations, with a reduction of concentrations in the final growth period probably by the 406

increasing use by plants in this phase. Consistently, there was an increase in the Fe 407

concentration in the substrate over the experimental period, but concentrations were lower 408

than recommended by Furlani (1998) and Furlani et al. (1999). High concentrations of 409

chloride and sodium were observed with both substrates, which were reduced by leaching and 410

tap water use instead of NS (Figure 5). 411

The increase in EC caused by the evaporation and salt accumulation increased the 412

substrate macro and micronutrient concentrations (Figure 5). This phenomenon is well 413

described in the literature, especially in the upper substrate layer (already cited in the pH and 414

EC discussion section). Unfortunately, we did not measure the EC or the nutrient 415

concentrations in layers, since the substrate thickness was less than 6 cm, what made the 416

layered measurements difficult. A decrease in EC and macronutrient concentrations on the 417

last growing day (DAT 29) was observed by the increased NS consumption from high plant 418

growth during this period (Figure 4), without reducing plant growth at the harvest. Both 419

substrate leaching and tap water application in the tank instead of NS did not significantly 420

reduce the substrate micronutrient concentrations (Figure 5). Another possible way to reduce 421

the substrate macro and micronutrient concentrations to avoid plant damages would be the 422

of 24

use of less concentrated NS with a lower EC, as the evaporation concentrates the nutrients 423

and increases the EC. 424

425

NS macro and micronutrients concentration 426

Weekly macronutrient concentrations of the NS varied according to the tank analyzed 427

(Figure 6). NO3-N, P, K, Ca, Mg and S values were higher in the NFT tank, and the pH and 428

NH4-N were higher in the WPB and WCC tanks. The EC was similar in both NS used (Figure 429

6). The P concentrations shown in Figure 6 were close to those recommended by Furlani 430

(1998) and Furlani et al. (1999) for lettuce. Concentrations of S were 50% lower than 431

recommended. There was a linear increase in the S concentration in the WPB and WCC tanks 432

over time (Figure 6). 433

There also were differences in weekly micronutrient concentrations in the NS among 434

tanks (Figure 6). Cu and Zn concentrations were higher in the NFT tank, while the values of 435

Fe, bicarbonate and chloride were higher in the WPB and WCC tanks. All the micronutrient 436

results presented in Figure 6 were close to the values recommended by Furlani (1998) and 437

Furlani et al. (1999) for lettuce, with the exception of Fe, which showed a value 30% lower 438

than recommended. There was a linear increase in Cu concentration over time in the NFT 439

tank and a quadratic trend over time in Fe in the WPB and WCC tanks (Figure 6). 440

Bicarbonate concentration was lower in the NFT treatment on DAT 15 and 22, 441

returning to the initial values of original water concentration at 29 DAT (Figure 6). In 442

general, this concentration was similar to the amounts supplied by the tap water. Chloride 443

was 7-8 times greater than the initial water concentration, and sodium was almost twice as 444

much as was initially present in the water (Figure 6). Bicarbonate, chloride and sodium 445

present in this experiment are within the acceptable limits indicated by Furlani (1998) and 446

Furlani et al. (1999) and did not cause any damage to plants. 447

of 24

The NS macro and micronutrients concentration were determined prior to the 448

replacement, and showed a significant increase in S, Cu, Fe, Mn, Zn and Na over time, 449

probably caused by the reduction of plant uptake as an effect of the higher temperature of NS 450

in NFT or yet by a higher supply than needed (Figure 6). 451

452

Conclusions 453

The wick irrigation system with self-compensating troughs, irrespective of substrate, 454

showed higher lettuce yield than the NFT system. However, the EC in WCC was more stable 455

than in WPB, facilitating nutritional management during the crop cycle without causing 456

salinity damage to the plants. Wick irrigation systems resulted in lettuce salable plants, being 457

an alternative for regions with high temperatures because of the substrate cooling effect, 458

limited manpower and electrical power. But the obtained biometric results did not prove a 459

standard technical superiority of the wick irrigation system over NFT but merely indicated 460

that, under the specific conditions applied in this experiment, the NFT system performed 461

poorly. Further investigations should be conducted in different seasons and with other 462

cultivars, trying to establish the water and nutrient management guidelines suitable for 463

different substrates to improve the utilization of this technology. 464

465

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Table 1. Hydrogen potential (pH), electrical conductivity (EC), and macro and micronutrient concentrations of pine bark and coconut coir

substrates. The results shown the average of three replications.

Substrate pH

EC NO3-N NH4-N P K Ca Mg S B Cu Fe Mn Zn Cl Na

(dS∙m-1) ----------------------------------------------------------- mg∙L-1 -----------------------------------------------------------

Pine bark 6.4 1 48.7 3.7 6.6 48.5 97.9 32.7 61.5 0.01 < 0.01 0.1 0.01 0.01 28.0 3.3

Coconut coir 5.6 0.3 0.4 0.2 1.5 94.7 6.5 1.9 6.5 0.30 0.05 0.9 0.04 0.10 16.3 4.4

of 4

Table 2. Root length, shoot diameter and height, root volume, leaf area, number of leaves, shoot (SFM) and root (RFM) fresh mass and shoot

(SDM) and root (RDM) dry mass at harvest of lettuce cv. ‘Vanda’ cultivated in different growing medias. The results shown the average of three

replications (twelve plants in each of the three troughs/channels).

Growing

media

Root

length

Shoot

diameter

Shoot

height

Root

volume Number of

leaves

Leaf area SFM SDM RFM RDM

(cm) (cm) (cm) z (mL) (cm2) --------------------- g∙plant-1 ---------------------

Pine bark 28.3 b 34.2 b 16.4 b 35.4 a 19.4 a 2.1 a 128.3 a 10.1 a 25.5 b 8.4 a

Coconut coir 32.4 a 36.4 a 17.9 a 38.8 a 20.6 a 2.2 a 131.3 a 11.1 a 31.8 a 8.0 a

NFT 12.5 c 26.5 c 17.6 a 6.1 b 19.6 a 1.2 b 54.9 b 8.1 b 10.5 c 5.3 b

Var. Coef. (%) 23.93 7.95 6.17 35.76 19.10 28.43 32.95 23.97 29.59 18.75

P <0.0001 <0.0001 0.069 <0.0001 NS <0.0001 <0.0001 <0.0001 <0.0001 <0.0001

z Analysis of variance performed with data transformed to √x. Means followed by different letters in the columns differ by Tukey’s test

according to the indicated probability (P). OBS.: NS = Not significant at 5% probability in Tukey’s test.

of 4

Table 3. Plant yield in fresh and dry basis, shoot/root ratio and leaf water content at harvest of lettuce plants cv. ‘Vanda’ cultivated in different

growing medias. The results show the average of three replications (twelve plants in each of the three troughs/channels).

Growing media

Plant yield

Shoot/root ratio Leaf water content (%) Fresh basis (kg∙m-2) Dry basis (kg∙m-2)

Pine bark 3.84 a 0.46 a 1.26 b 90.92 a

Coconut coir 4.08 a 0.47 a 1.54 a 84.50 b

NFT 1.63 b 0.33 b 1.43 ab 91.12 a

Var. Coef. (%) 30.51 16.29 29.27 4.59

P <0.0001 <0.0001 0.0147 <0.0001

Means followed by different letters in the columns differ by Tukey’s test according to the indicated probability (P).

of 4

Table 4. Shoot and root macro and micronutrient concentrations at harvest of lettuce cv. ‘Vanda’ cultivated in different growing medias. The

results show the average of three replications.

Tissue

Growing N P K Ca Mg S B Cu x Fe Mn Zn

media ----------------------- g∙kg-1 of dry weight -------------------- ------------------- mg∙kg-1 of dry weight ------------------

Shoot

Pine bark 50.4 a 7.0 a 68.9 a z 14.7 a 4.8 a 3.3 b 29.6 b 3.9 c 268.0 c 84.7 a z 58.5 b

Coconut coir 46.4 b 6.7 a 87.3 a z 10.7 b 3.2 b 3.3 b 39.4 a 7.9 b 437.0 a 155.7 a z 54.8 b

NFT 44.1 b 4.7 b 36.8 b z 12.2 b 2.7 b 5.1 a 40.9 a 43.6 a 331.3 b 151.7 a z 234.7 a

VC (%) 3.39 11.41 6.61 5.81 6.37 1.92 8.07 5.70 6.10 24.14 11.84

P 0.0079 0.0156 0.0005 0.0014 <0.0001 <0.0001 0.0066 <0.0001 0.0002 NS <0.0001

Root

Pine bark 9.8 b z 1.8 b z 7.0 c 12.7 a z 6.2 a 1.5 b x 27.6 b 17.0 c 7.391.7 b 118.3 a 33.3 b

Coconut coir 11.9 b z 2.2 b z 18.7 b 7.4 b z 3.6 b 1.4 b x 34.9 b 23.3 b 6.124.3 b 84.7 b 35.3 b

NFT 40.4 a z 11.6 a z 31.7 a 7.6 b z 1.6 c 4.9 a x 62.8 a 3,061.6 a 12,203.7 a 61.0 c 1,058.8 a

VC (%) 5.52 9.52 11.53 4.94 8.95 25.10 13.51 5.98 12.91 7.91 25.46

P <0.0001 0.0001 <0.001 0.0012 <0.0001 0.0003 0.0006 <0.0001 0.0012 0.0002 <0.0001

z Analysis of variance performed with data transformed to 1/√x. x Analysis of variance performed with data transformed to log(x). Means

followed by different letters in the columns differ by Tukey’s test according to the indicated probability (P). OBS.: NS = Not significant at 5%

probability in Tukey’s test. VC = Variation coefficient.

of 6

Figure 1. Schematic of the self-compensating trough, showing (A) the front view, (B) cross-

section (section C-C’), and (C) sectional side view. Dimensions in mm. The compartments

are also indicated: (1) substrate deposition chamber, (2) wick strips of synthetic non-woven

mat (SNWM), (3) orifice for SNWM insertion spaced every 0.4 m, (4) lower reservoir for

nutrient solution storage, and (5) drainage orifice.

3 1

4 2

Section c-c’

4

2

c 3

c’ 1

3

2

4

5

1

A

B

C

of 6

Figure 2. Wick irrigation system with leveled self-compensating troughs installed on a wood

support, micro reservoir with height regulation using mini float switch and tank.

Self-compensating troughs

Micro reservoir with

height regulation using

mini float switch

50 L-tank

Nutrient solution supply system

of 6

Days after transplanting (DAT)

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Rela

tive h

um

idit

y (

%)

10

20

30

40

50

60

70

80

90

100T

em

pera

ture

(oC

)

0

10

20

30

40

50

60

Relative humidity

Temperature

Figure 3. Temperature and relative humidity inside the greenhouse during the experimental

period. Horizontal dotted lines indicate the maximum (25 oC) and the minimum (15 oC)

temperature values for optimal lettuce growth.

of 6

1 3 5 7 911

13

15

17

19

21

23

25

27

29

4

5

6

7

8

9

2D Graph 2

pH

4

5

6

7

8

9

4

5

6

7

8

9Pine bark/

WPB

Hydroponics/

NFT

Coconut coir/

WCC

0

2

4

6

8Pine bark/

WPB

Ele

ctr

ica

l c

on

du

cti

vit

y,

EC

(m

S. c

m-1

)

0

2

4

6

8


1 3 5 7 911

13

15

17

19

21

23

25

27

290

2

4

6

8NS

Rep. 1

Rep. 2

Rep. 3

Hydroponics/

NFT

Coconut coir/

WCC

Figure 4. Variation of the hydrogen potential (pH) and electrical conductivity (EC) values of

pine bark (WPB) and coconut coir (WCC) substrates and hydroponics (NFT) nutrient

solution (NS). The black arrows indicate the addition of tap water to the tanks. The gray

arrows indicate substrate leaching with water to reduce the EC. The white arrows indicate

weekly replacement of NS to avoid nutrient concentration fluctuations.

of 6

N-N

itra

te,

N-N

O3 (

mg

. L-1)

20

40

60

80

100

120

140

160

180

Pine bark (WPB)

Coconut coir (WCC)

pH

4.6

4.8

5.0

5.2

5.4

5.6

5.8

6.0

6.2

N.S.

Ele

ctr

ical co

nd

ucti

vit

y (

mS

. cm

-1)

0.5

1.0

1.5

2.0

2.5

3.0

EC WCC = 0.446 + 0.115*DAT - 0.00316*DAT2

R2 = 0.48

P = 0.019

N-A

mo

nia

cal, N

-NH

4 (

mg

. L-1)

-5

0

5

10

15

20

25

30

N-NH4 WCC = 7.082 + 1.710*DAT - 0.0554*DAT2

R2 = 0.56

P = 0.039

Ph

osp

oru

s,

P (

mg

. L-1)

15

20

25

30

35

40

45

P WCC = 13.985 + 3.165*DAT - 0.0996*DAT2

R2 = 0.55

P = 0.032P

ota

ssiu

m,

K+ (

mg

. L-1)

100

150

200

250

300

350

400

450

K+

WCC = 88.433 + 35.903*DAT - 1.000*DAT2

R2 = 0.72

P = 0.001

N.S.

Calc

ium

, C

a+

2 (

mg

. L-1)

0

50

100

150

200

250

N.S.

Mag

nesiu

m,

Mg

+2 (

mg

. L-1)

0

20

40

60

80

N.S.

Su

lfu

r, S

-SO

4 (

mg

. L-1)

0

20

40

60

80

100

S-SO4 WCC = 8.482 - 0.152*DAT

R2 = 0.42

P = 0.022 Bo

ron

, B

(m

g. L

-1)

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7B WCC = 0.133 + 0.0373*DAT - 0.000998*DAT

2

R2 = 0.50

P = 0.015

Co

pp

er,

Cu

+2 (

mg

. L-1)

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Iro

n,

Fe

+2 (

mg

. L-1)

-0.5

0.0

0.5

1.0

1.5

2.0

Fe+2

WPB = 0.661 - 0.0517*

DAT + 0.00160*DAT2

Fe+2

WCC = - 0.0703 + 0.0409*DAT

R2 = 0.774

P < 0.0001

R2 = 0.603

P = 0.016


8 15 22 29

Man

gan

ese,

Mn

+2 (

mg

. L-1)

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

N.S.


8 15 22 29

Zin

c,

Zn

+2 (

mg

. L-1)

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

Zn+2

WCC = -0.190 +

0.0419*DAT - 0.00104*DAT2

R2 = 0.60

P = 0.001


8 15 22 29

Ch

lori

de,

Cl- (

mg

. L-1)

150

200

250

300

350

Cl- WCC = 12.439 + 22.373*DAT - 0.554*DAT

2

R2 = 0.70

P = 0.003


8 15 22 29

So

diu

m,

Na

+ (

mg

. L-1)

15

20

25

30

35

40

Na+ WCC = 6.125 + 2.819*DAT - 0.0669*DAT

2

R2 = 0.63

P = 0.015

Cu+2

WPB = 0.00605 + 0.000154*Dia

R2 = 0.38

P = 0.034

Figure 5. Weekly hydrogen potential (pH), electrical conductivity (EC), macro and

micronutrients, chloride and sodium concentrations determined in different substrates with

lettuce cv. ‘Vanda’ plants. Each point indicates the average of three replications ± standard

error. The absence of regression lines indicates no significant trend (P > 0.05).

of 6

Mag

nesiu

m,

Mg

+2 (

mg

. L-1)

26

28

30

32

34

36

38

40

Su

lfu

r, S

-SO

4 (

mg

. L-1)

11.0

11.5

12.0

12.5

13.0

13.5

14.0

14.5

15.0

NFT tank

WPB/WCC tank

Ph

osp

oru

s,

P (

mg

. L-1)

20

22

24

26

28

30

32

P WPB and WCC tank = 31.7433 -

0.6807*DAT + 0.0183*DAT2

R2 = 0.9995

P = 0.0228

S-SO4 NFT tank =

10.3905 + 0.1418*DAT

R2 = 0.9501

P = 0.0253

pH

4.4

4.6

4.8

5.0

5.2

5.4

5.6

5.8

6.0

6.2

6.4

6.6

Ele

ctr

ical co

nd

uti

vit

y,

EC

(m

S. c

m-1)

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

Nit

rog

en

, N

(m

g. L

-1)

0

20

40

60

80

100

120

140

160

180

200

N-NO3 NFT

N-NO3 wick tanks

N-NH4 NFT

N-NH4 wick tanks

Po

tassiu

m,

K+ (

mg

. L-1)

190

200

210

220

230

240

250

Calc

ium

, C

a+

2 (

mg

. L-1)

125

130

135

140

145

150

155

160

N.S. N.S. N.S.

N.S. N.S.N.S.

Co

pp

er,

Cu

+2 (

mg

. L-1)

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Iro

n,

Fe

+2 (

mg

. L-1)

0.5

1.0

1.5

2.0

2.5

3.0 Fe+2

PB and CC tank = 1.6942 -

0.0496*DAT + 0.0029*DAT2

R2 = 0.9997

P = 0.0174

Man

gan

ese,

Mn

+2 (

mg

. L-1)

0.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48Mn

+2 PB and CC tank = 0.4672 - 0.0149*DAT +

0.0004*DAT2

R2 = 0.9999

P = 0.0122

Cu+2

NFT tank = - 0.1841 + 0.1011*DAT

R2 = 0.9750

P = 0.0126

Bo

ron

, B

(m

g. L

-1)

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48

0.50

N.S.


8 15 22 29

Zin

c,

Zn

+2 (

mg

. L-1)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5Zn

+2 NFT tank = - 0.4536 + 0.0879*DAT

R2 = 0.9361

P = 0.0325


8 15 22 29

Bic

arb

on

ate

(m

g. L

-1)

0

20

40

60

80

100

120

N.S.


8 15 22 29

So

diu

m,

Na

+ (

mg

. L-1)

16

18

20

22

24

26

28Na

+ NFT tank = 16.0936 + 0.3276*DAT

R2 = 0.9998

P < 0.0001

R2 = 0.9512

P = 0.0247

Na+ WPB and WCC tank =

14.4859 + 0.3326*DAT


8 15 22 29

Ch

lori

de,

Cl- (

mg

. L-1)

100

120

140

160

180

200

N.S.

Figure 6. Weekly hydrogen potential (pH), electrical conductivity (EC), macro and

micronutrients, bicarbonate, chloride and sodium concentrations at different nutrient

solutions used for lettuce cv. ‘Vanda’ cultivation. Each point indicates the average of three

replications ± standard error. There were no significant regression curves for nutrients in the

NFT tank. The absence of regression lines indicates no significant trend (P > 0.05).

performance of wick irrigation system using self-compensating benches with substrates for lettuce...

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