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Journal of Plant Nutrition
ISSN: 0190-4167 (Print) 1532-4087 (Online) Journal homepage: http://www.tandfonline.com/loi/lpla20
Performance of wick irrigation system using self-
compensating troughs with substrates for lettuce
production
Rhuanito Soranz Ferrarezi & Roberto Testezlaf
To cite this article: Rhuanito Soranz Ferrarezi & Roberto Testezlaf (2016) Performance of wick
irrigation system using self-compensating troughs with substrates for lettuce production,
Journal of Plant Nutrition, 39:1, 150-164, DOI: 10.1080/01904167.2014.983127
To link to this article: http://dx.doi.org/10.1080/01904167.2014.983127
Accepted author version posted online: 17
Nov 2014.
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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, S~
ao Paulo, Brazil
ARTICLE HISTORY
Received 19 March 2013
Accepted 24 February 2014
ABSTRACT
Subirrigation systems in which water and nutrients are supplied to the
substrate through wick strips for upward nutrient solution (NS) movement can
be a feasible alternative to improve lettuce quality with low environmental
pollution, enabling production with reduced labor and electricity or in regions
with high air temperature. The objective of this study was to compare the
performance of two wick irrigation systems using self-compensating troughs
filled with either pine bark (WPB) or coconut coir (WCC) with nutrient film
technique (NFT) hydroponic system for greenhouse lettuce production. The
daily monitoring of electrical conductivity (EC) and pH allowed the experiment
management according to the recommended values for optimal lettuce
growth. The EC showed variation among troughs and salt accumulation in
substrates, with WPB exhibiting two times greater EC than WCC (ranging from
0.95 to 7.57 and from 0.68 to 3.67 dS¢m
¡1
, respectively), while the pH values
were stable over time. The WCC promoted greater root length and shoot
diameter, while WPB produced shorter plants compared to the other two
treatments. NFT resulted in an 83% lower leaf area and 44% lower root volume
than WPB and WCC. The fresh and dry shoot masses with NFT were 58% and
24% lower than with WPB and WCC, respectively. The fresh root mass was also
reduced in NFT plants, which was 67% smaller than WCC and 59% smaller
than WPB. Root dry mass of NFT was 35% lower than the average of WPB and
WCC. Nitrate (NO
3
)-nitrogen (N), ammonium (NH
4
)-N, phosphorus (P),
potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), copper (Cu),
iron (Fe), manganese (Mn), and zinc (Zn) concentrations in plant shoot and
root at the end of the experiment as well as the same nutrients, chloride,
sodium, and bicarbonate concentrations in substrate and NS determined
weekly differed among the treatments (P<0.01). The EC and nutrient
concentration in the substrates increased over time. The wick irrigation system
with both substrates resulted in higher productivity than NFT, with higher yield
and plant quality in WCC, indicating its feasibility as an alternative system for
lettuce production in greenhouses. However, due to the salinity buildup, water
and nutrition management needs to be optimized for self-compensating
troughs to avoid an increase in substrate EC over time.
KEYWORDS
subirrigation; hydroponics;
nutrient concentration;
Lactuca sativa L. ‘Vanda’,
greenhouse; NFT
Introduction
Lettuce (Lactuca sativa L.) is the most consumed salad vegetable in Brazil (Santos et al., 2010), repre-
senting 50% of all leafy vegetables commercialized in the food supply distribution centers in the coun-
try (Moretti and Mattos, 2008). Currently, lettuce is grown both in soil and hydroponic systems. In
CONTACT Rhuanito Soranz Ferrarezi rhuanito@terra.com.br School of Agricultural Engineering, University of Campinas, 501
C^
andido Rondon Street, Campinas, 13083-875 S~
ao Paulo, Brazil
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpla.
© 2016 Taylor and Francis Group, LLC
JOURNAL OF PLANT NUTRITION
2016, VOL. 39, NO. 1, 150–164
http://dx.doi.org/10.1080/01904167.2014.983127
Downloaded by [UVI Library] at 11:49 11 January 2016
soil, the cultivation occurs in raised beds, where plants are subjected to diverse weather conditions,
which can result in variable plant yields and quality reduction (Feltrim et al., 2009). Furthermore, con-
secutive years of crop production promotes the contamination of soil and groundwater with nutrients
and pesticides. The most used hydroponics system in lettuce production is the nutrient film technique
(NFT) (Cometti et al., 2008; Feltrim et al., 2009).
Nutrient film technique hydroponics promotes efficient use of greenhouse area and higher yield
(Santos et al., 2010), with better crop quality (Lopes et al., 2007 and Santos et al., 2010) and shortened
crop cycles due to better environmental control (Martins et al., 2009; Santos et al., 2010), allowing
year-round cultivation and harvesting (Helbel Junior et al., 2008). The advantages also include higher
water and fertilizer use efficiency, with the possibility of NS reuse, resulting in environmental preserva-
tion by reducing fertilizer leaching, pesticide runoff and groundwater contamination (Martins et al.,
2009; Santos et al., 2010). There is also a potential for reducing labor use during crop production (Mar-
tins et al., 2009). However, hydroponics presents challenges for growers, as dependence on electric
power for nutrient solution (NS) circulation and aeration and the risk of losing the entire production if
a prolonged power outage occurs (da Silva et al., 2005), and difficulty of adoption in regions with high
air temperature due to high temperature of the NS, which complicates plant establishment and man-
agement (Alberoni, 1998). The requirement of technical knowledge and permanent support and the
possibility of pathogen dissemination due to NS recirculation are also major concerns (Resh, 2002).
To improve crop quality, enable lettuce cultivation in regions with limited manpower and electricity
or with high air temperatures, and reduce environmental pollution, new production systems are being
developed. Subirrigation systems in which water and nutrients are supplied to the substrate through
capillary action (Caron et al., 2005) and hydraulic redistribution (Prieto et al., 2012) can be viable
alternatives.
A wick irrigation system operates in a closed cycle, without runoff, permitting appropriate plant nutri-
tion and creating alternatives to improve production uniformity. These systems show major advantages:
1) independence of electricity for operation (Andriolo et al., 2004); 2) high water and nutrient use effi-
ciency (Son et al., 2006); 3) less need for manpower, as the management is simplified compared with con-
ventional cultivation, providing cost reduction (Andriolo et al., 2004); 4) increase in the uniformity and
quality of production (Oh and Son, 2008); 5) water savings (Laviola et al., 2007); and 6) temperature con-
trol of the root system (Laviola et al., 2007). Wick irrigation systems can be used for the cultivation of
ornamental plants, such as chrysanthemums and poinsettias (Kang et al., 2009), kalanchoe (Lee et al.,
2010) and cyclamen (Oh and Son, 2008). Ferrarezi et al. (2012) suggested that wick irrigation systems
might be used in the production of vegetables or condiment and aromatic plants.
Several studies using the wick irrigation system were performed with different equipment for many
crops and environmental conditions. The results from these studies revealed the optimum wick width
and suitable water depth for wick contact (Kang et al., 2009), the wick length to improve water distri-
bution (Lee et al., 2010; Son et al., 2001), the possibility of covering the substrate surface to reduce
evaporation (Son et al., 2006), the suitable size of the growing container (Lee et al., 2010), the substrate
composition for satisfactory root wetting and moisture maintenance (Lee et al., 2010; Oh et al., 2007),
the possibility of disease incidence and spread (Lee et al., 2010 and Oh and Son, 2008), and efficiency
equipment use (Laviola et al., 2007).
At the present time, the Brazilian market only has one commercial wick system available, called self-
compensating troughs. This wick irrigation system was evaluated by Ferrarezi et al. (2012), showing
that the equipment had some imperfections in the lower reservoir for NS storage, determining signifi-
cant differences among the water depth, time and filling volume, and uniformity of water distribution
(UWD) in two commercial substrate (pine bark and coconut coir, same systems used at this experi-
ment). They found higher moisture and UWD in pine bark. According to Andriolo et al. (2004), the
use of substrates allowed the reduction of approximately 92.4% of pump operation time compared
with NFT, simplifying both fertigation management and NS control. However, studies evaluating the
performance of the wick irrigation system for lettuce production using different substrates for cultiva-
tion in Brazil remain scarce. The hypothesis of this research is that wick irrigation system promotes
higher lettuce production compared to NFT in greenhouses.
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Thus, the objective of this study was to compare the performance of two wick irrigation systems
using self-compensating troughs filled with either pine bark or coconut coir with NFT for lettuce pro-
duction in a greenhouse. This technical information can support decision-making situations when
wick or NFT systems are appropriate.
Material and methods
Location
The experiment was performed at the School of Agricultural Engineering (FEAGRI), University of
Campinas (UNICAMP), in Campinas, SP, Brazil, from 22 June to 20 July 2010. Experimental plots
were assembled in a Venlo-type greenhouse, covered with 150 mm-thick agricultural polyethylene film,
with 18.2£6.4£3 m (length x wide x ceiling), without roof vents, with a 0.87x0.30-mm frontal and side
anti-aphid screen and a 40-cm masonry bottom.
Plant material
Seedlings of lettuce ‘Vanda’(Sakata Seeds, Bragan¸ca Paulista, SP, Brazil) grown in Styrofoam trays with
coconut coir substrate for 28 days were purchased from a nursery (Selma Mudas, Bragan¸ca Paulista,
SP, Brazil), and transplanted into the experimental plots on 18 June 2010, and irrigated daily to ensure
proper plant rooting.
Water and NS
The water we used was from the municipal system and had the following chemical characteristics: pH
D7.1, electrical conductivity (EC) D0.2 dS¢m
¡1
and nutrients (mg¢L
¡1
): nitrate (NO
3
)-nitrogen (N)
D2.3, ammonium (NH
4
)-N D0.4, phosphorus (P) D1.5, potassium (K) D14.8, calcium (Ca) D13,
magnesium (Mg) D2.1, sulfur (S) D1.7, boron (B) D0.1, copper (Cu) D<0.01, iron (Fe) D0.1, man-
ganese (Mn) D0.02, zinc (Zn) D0.01, chloride D23.4, sodium (Na) D12.3 and bicarbonate D100.4.
The NS used throughout the experimental period was prepared using 3 mL¢L
¡1
of FloriSol Veg
(Conplant Ferti, Campinas, SP, Brazil) and 0.3 g¢L
¡1
of magnesium sulfate (Produqu
ımica, Suzano,
SP, Brazil), with pH D4.24, EC D1.8 dS¢m
¡1
and the nutrient concentrations (mg¢L
¡1
): total-N D
198 (NO
3
-N D174 and NH
4
-N D24), P D31, K D187, Ca D143, Mg D60, S D36, B D0.5, Cu D
0.5, Fe D1.8, Mn D0.5, Mo D0.1, nickel (Ni) D0.1 and Zn D0.2. The pH was kept between 5.5 to
6.5 using phosphoric acid (H
3
PO
4
) or potassium hydroxide (KOH) 1 N solution to maintain the che-
lates in a stable form (Ferrarezi et al., 2007), with daily replenishment (Furlani et al., 1999) and weekly
replacement to avoid nutrient concentration fluctuations.
Treatments and substrates
We evaluated three treatments: a wick irrigation system with coconut coir substrate (WCC), a wick
irrigation system with pine bark substrate (WPB), and a nutrient film technique hydroponics system
(NFT). The substrates used were coconut coir Golden Grain Mix (Amafibra, Ananindeua, PA, Brazil)
and pine bark Citrus 9 (Mec Plant, Tel^
emaco Borba, PR, Brazil). Both substrates were analyzed prior
to transplanting for macro and micronutrient determination at the Substrate Analysis Laboratory
(Instituto Agron^
omico de Campinas, Campinas, SP, Brazil) using Sonneveld and van Elderen (1994)
extraction method (Table 1).
Wick irrigation system
The troughs for wick irrigation were made out of polypropylene and were resistant to chemical action.
The equipment consisted of two compartments: a lower reservoir for NS storage (bottom) and a
152 R. S. FERRAREZI AND R. TESTEZLAF
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substrate deposition chamber (top), which were interconnected by a wick strip of synthetic non-woven
mat (SNWM) (Figure 1). This wick conducted NS from the bottom to the top compartment, wetting
the substrate and supplying water and minerals to plants (Ferrarezi et al., 2012).
The complete wick irrigation system consisted of a 50-L tank (Puma Tambores, Piracicaba, SP,
Brazil), 32-mm water supply hose (Tramontina, Recife, PE, Brazil), 2-L micro reservoir and five
self-compensating troughs (Hidrogood Horticultura Moderna, Tabo~
ao da Serra, SP, Brazil) per
experimental plot (Figure 2). These 0.175£4.0£0.7 m (width x length x height) troughs were rec-
ommended for leafy vegetables production and had a 26-L capacity in the substrate deposition
chamber and 9-L in the lower reservoir for NS storage. The micro-reservoir had a mini float that
regulated the solution flowing from the tank connected to the lower reservoir through polyvinyl
chloride (PVC) pipes. The NS supply was mediated by gravity, requiring leveled installation of
troughs and micro-reservoir. As the plant absorbed water and nutrients from the substrate, the
wick automatically replenished the solution. Thus, the plant regulated the solution flow to the
substrate by the difference in total potential and capillary action, without requiring automated
controls, pumps, emitters, etc. (Ferrarezi et al., 2012). One plot with five troughs was assembled
for each wick treatment tested (one with coconut coir and another with pine bark substrate).
The countertop was 1.2£4.0 m (width x length) and completely leveled. The seedlings were
spaced every 0.25 m, totaling 15–16 plants per trough.
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 NO
3
-N NH
4
-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
Figure 1. Schematic of the self-compensating trough, showing A) the front view, B) cross-section (section C-C0), 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.
JOURNAL OF PLANT NUTRITION 153
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NFT hydroponic system
The NFT system was composed of an underground 250-L tank (Acqualimp, Valinhos, SP, Brazil), an
0.85-HP irrigation pump (Hydrobloc C800T, KSB, V
arzea Paulista, SP, Brazil), timer (MT-2001, Did-
ziel, S~
ao Paulo, SP, Brazil), 32-mm water supply pipe (Tigre, Joinville, SC, Brazil), five 90 mm x 4 m
(width x length) trapezoidal hydroponic channels (Hidrogood Horticultura Moderna, Tabo~
ao da Serra,
SP, Brazil) and 75-mm drain pipe (Tigre, Joinville, SC, Brazil). The countertop was 1.2£4.0 m (width x
length), with a 6% slope to allow NS return to the tank and a 1 L¢min
¡1
flow rate per channel, both rec-
ommended by Furlani et al. (1999) for Brazilian conditions. The seedlings were spaced every 0.25 m,
totaling 15–16 plants per channel. During the first 10 days of the experiment, a timer activated the
pump for 5 min at 15-min intervals from 7 am to 5 pm due to the small plant size. From day after
transplant (DAT) 11 until the end of the experiment, the pump was turned on continuously from 7 am
until 5 pm because lettuce grown in high temperature regions require a continuous supply of NS
(Graves, 1983; Graves and Hurd, 1983) or intervals of up to 5 min to promote adequate plant watering
and nutrition (Zanella et al., 2008). From 5 pm to 7 am, the system was irrigated for 5 min every 2 h.
Parameters evaluated
The temperature and relative humidity inside the greenhouse were monitored every 5 min using a digi-
tal thermo-hygrometer (HT-4000, ICEL, Manaus, AM, Brazil) mounted at the same height as the self-
compensating troughs (0.7 m above the soil surface). All recordings throughout the experimental
period were stored in a data logger.
The EC and pH in the substrates and in the NS from NFT and wick tanks were monitored daily. For
the substrates, an adaptation of the 1:1.5 Dutch extraction method from Sonneveld and van Elderen
(1994) was used: removal of 100 mL sample from each substrate, addition of 150 mL of tap water, stir-
ring for 30 minutes and standing for 30 minutes. For the NS analyses, a sample from the NFT treat-
ment was collected from each channel, and a sample from each wick irrigation system was directly
collected from each tank. The solutions were then transferred to individual test tubes, and EC and pH
readings were taken (DM-31 conductivity meter and a DM-21 pH meter, Digimed, S~
ao Paulo, SP, Bra-
zil). When the substrate EC reached values higher than the double recommended for lettuce produc-
tion, equals to 4 dS¢m
¡1
in the average of the three troughs, only tap water was added in the WPB and
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.
154 R. S. FERRAREZI AND R. TESTEZLAF
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WCC tanks or leached all the substrate in the troughs with tap water, to avoid plant damage caused by
salt excess. Tap water applications to replace NS occurred on DAT 7, 10, and 14 in WPB, and DAT 14
in WCC. Substrate leaching was performed on DAT 9 and 12 only in WPB.
The biometric parameters –root length, shoot diameter and height, root volume (determined
through water volume displacement in a graduated cylinder, according to Sant’ana et al., 2003), num-
ber of leaves, and leaf area of all experimental plants (determined using a Li-Cor 3100 leaf area meter,
from Li-Cor, Lincoln, NE, USA) –were taken at DAT 28. The plants were then separated into shoots
(leaves Cstems) and roots for shoot (SFM) and root (RFM) fresh mass determination. This material
was dried in an 85C oven with forced circulation (MA 037, Marconi Equipamentos de Laborat
orio
Ltda, Piracicaba, SP, Brazil) to obtain shoot (SDM) and root (RDM) dry mass. The plant yield based
on fresh and dry mass was expressed per unit area. The leaf water content was calculated as [(SFM -
SDM) / SFM] x 100%.
Chemical analysis of N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn were performed at harvest in shoot
and root, substrate, and NS samples at the Soil, Plant, and Substrate Analysis Laboratory (Instituto
Agron^
omico de Campinas, Campinas, SP, Brazil). For shoot and root, the method described by Bata-
glia et al. (1983) was used in three plants per replication from the same samples used for the fresh and
dry mass determination. For substrate, the N steam distillation method indicated by Cantarella and
Trivelin (2001) was used, and inductively coupled plasma optical emission spectrometry (ICP-OES)
was used for the other nutrients. Three substrate samples per replication were collected weekly, with
solution extraction being performed according to the 1:1.5 Dutch method (Sonneveld and van Elderen,
1994). The same method for NS, plus chloride determination by ion-selective electrode, sodium using
photometry, and bicarbonate through potentiometric titration was used in samples collected weekly
after water replenishment and before the weekly replacement.
Experimental design and statistical analysis
The experimental design was a completely randomized block, with three treatments and three replica-
tions. Twelve plants were harvested from the center three troughs/channels for the biometric analysis,
totaling 36 plants per treatment. All results were tested using the Shapiro-Wilk normality test and
transformed adequately when necessary. The biometric parameters, plant yield, shoot: root ratio, leaf
water content and tissue nutrient concentration data (shoot and root) were subjected to analysis of var-
iance and Tukey’s mean separation (SAS 9.2, SAS Institute, Cary, NC, USA). Over time, changes in
nutrient concentration in the NS and substrates were analyzed by regression models (Sigma Plot 11,
Jandel Scientific, Corte Madera, CA). The results were considered significant when P<0.05.
Results and discussion
Climatic parameters
The high temperature in the greenhouse varied between 45 to 50C from DAT 1 to 16, and then
decreased due to weather conditions (Figure 3), exceeding the optimum range of 15–25C recom-
mended by Helbel Junior et al. (2008), dos Santos et al. (2009), and Martinez (2006) for lettuce. There
was a decrease in temperature and an increase in relative humidity in the final third of experimental
period because of cooler weather.
A negative effect of the temperature in the NFT treatment was detected, resulting in smaller plants
than the substrate treatments, as a consequence of the air (Figure 3) and the NS temperature. The aver-
aged weekly temperature of the NS in the NFT tank was 32C, and in wick irrigation system tanks was
28C (data not shown). All temperatures exceeded the range of 18–24C for summer and 10–16C for
winter recommended by Alberoni (1998) to maintain a higher oxygen concentration for root respira-
tion and metabolic reactions in the roots (Helbel Junior et al., 2008). L
opez-Pozos et al. (2011) indi-
cated that low oxygenation in recirculating hydroponics induces root hypoxia as a result of low oxygen
solubility, especially in warm climates, reducing crop yield. According to dos Santos et al. (2009), high
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temperatures of NS can negatively influence lettuce plant architecture, weight, quality, and yield. The
greenhouse did not provide any temperature control and the frontal side was built with an anti-aphid
screen, which reduced the air movement and can contributed to heating. This screen was used because
this greenhouse was set up for citrus seedling production, following the vegetable sanitary protection
guidelines and plant protection conformity certification for citrus seedlings production in S~
ao Paulo
State (Coordenadoria de Defesa Agropecu
aria do Estado de S~
ao Paulo, 2005). One of the reasons for
the high NS temperatures could be the pump overheating due to its over sizing for the small dimen-
sions of the experimental plot and the metal pump casing, which warmed the solution during continu-
ous pumping.
Daily monitoring of the EC and pH
The EC varied among the troughs throughout the experimental period as a result of salt accumulation
in the WPB and WCC substrates (Figure 4). In WPB, EC was more than twice than that in WCC
(ranged from 0.95 to 7.57 and from 0.68 to 3.67 dS¢m
¡1
, respectively), perhaps due to the increased
evaporation from the growing media as compared with WCC (Lopes et al., 2007). These EC values
were higher than recommended for lettuce by Furlani et al. (1999) (1.6 to 1.8 dS¢m
¡1
) and Castellane
and Ara
ujo (1995) (up to 2.5 dS¢m
¡1
). This increase in EC was faster at the beginning of the experi-
ment (DAT 7) because the plants did not fully cover the substrate surface, thus increasing evaporation.
However, EC also increased in the middle of the experiment in WCC (DAT 13). The salt accumulation
in WPB induced typical edge-burn symptoms in older leaves due to salt excess.
When plants are subirrigated, an increase in the EC at the upper substrate layer is frequently
observed due to the evaporation and salt concentration (Dole et al., 1994; Argo and Biernbaum, 1995;
Rouphael and Colla, 2005; Rouphael et al., 2006). Santos et al. (2010) showed that high EC can reduce
the number of lettuce leaves, stem diameter, shoot fresh and dry mass, and water content.
The most common management strategies used to reduce EC include the use of NS with lower EC,
periodic substrate leaching, or addition of tap water to the tanks. The last two strategies were used to
reduce the EC of the substrate when it increased over the recommended. The substrates were leached
on DAT 8 and 11, and we used tap water instead of NS on DAT 7, 11, and 14, effectively reducing the
concentration of all nutrients in WPB, with a consequent reduction in pH and EC (Figure 4). There-
fore, the EC of the NS was close to zero twice in WPB and once in WCC (Figure 4), allowing the EC
reduction in the substrate and plant growth recovery. However, this substrate EC subsequently
increased again, which could be a challenge to growers due to the constant requirement of monitoring
and management of EC to avoid plant damage (Figure 4). Furthermore, this procedure was time con-
suming, resulting in significant volumes of water wasted to the environment due to disposal of the NS
in the greenhouse soil, which can be the major limitation of the wick irrigation system. In addition, the
Figure 3. Temperature and relative humidity inside the greenhouse during the experimental period. Horizontal dotted lines indicate
the maximum (25C) and the minimum (15C) temperature values for optimal lettuce growth.
156 R. S. FERRAREZI AND R. TESTEZLAF
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use of tap water in substrate-grown crops may introduces bicarbonates at high concentrations depend-
ing also on the bicarbonate concentration in the irrigation water, which in most cases is excessively
high, thereby resulting in very high pH levels in the root zone, being an undesired impact. In the pres-
ent study, the bicarbonate concentration in the irrigation water was not very high.
The pH of the NS showed spikes in the WPB treatment due to the use of tap water in the tank for
substrate leaching to reduce EC in the self-compensating troughs (Figure 4, WPB). In addition, the pH
of the NS in the WCC treatment was higher than WPB during the entire production cycle, and spiked
when tap water was added to the tanks (Figure 4, WCC). Measurements in the NFT treatments were
relatively consistent throughout the experimental period, as a result of using the same NS in all chan-
nels (Figure 4, NFT).
Biometric parameters
At harvest, the WCC treatment resulted in 13% longer roots than WPB and 61% longer than NFT
(Table 2,P<0.0001). Those were similar to the results of Silva et al. (2005). NFT was approximately
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.
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one-third lower than the other two substrates. A similar effect was observed with shoot diameter in
WCC, which was 6% larger than WPB and 27% larger than with NFT (Table 2,P<0.0001). The shoot
diameter responses for WPB and WCC were similar to those observed by Santos et al. (2010), and
higher than reported by Feltrim et al. (2009) and Helbel Junior et al. (2008). However, NFT plants had
smaller shoot diameter than that observed by these authors. The WPB treatment had shorter plants
than the other two treatments (Table 2,PD0.0069).
The plants from the NFT treatment produced 83% less root volume and 44% smaller leaf area than
the average of the WPB and WCC treatments (Table 2,P<0.0001). These results differ from those of
da Silva et al. (2005), who found no difference for these variables between the hydroponic and the cap-
illary wick system. Root volume and leaf area (Table 2,P<0.0001) were higher than those found by
da Silva et al. (2005), who also used wick irrigation, similar to those obtained by Santos et al. (2010) for
‘Vera’. The present results were 50% lower than those of Feltrim et al. (2009) and Zanella et al. (2008),
most likely due to the shorter crop cycle (28 days) in the present experiment. The number of leaves did
not differ among the treatments (Table 2,P>0.05).
The NFT treatment produced plants with 58% and 24% lower SFM and SDM, respectively, than
with both substrates (Table 2,P<0.0001). Comparing these results with other studies using hydro-
ponics, the SFM in NFT (54.1 g¢plant
¡1
) was similar to the reported by Santos et al. (2010) (58
g¢plant
¡1
) and lower than Feltrim et al. (2009) (338.99 g¢plant
¡1
) and Helbel Junior et al. (2008) (413.4
g¢plant
¡1
). In WPB and WCC substrates (130 g¢plant
¡1
), SFM was three times higher than observed
by Silva et al. (2005)(40 g¢plant
¡1
). The SDM treatments grown in substrates was two times higher
than that observed in Martins et al. (2009) (equal to 5.68 g plant
¡1
at 30 days after transplanting), and
five times greater than da Silva et al. (2005); notably, similar results were reported by Cometti et al.
(2008) and Zanella et al. (2008).
RFM was also reduced in NFT treatment, which was 67% lower than WCC and 59% lower than
WPB (Table 2,P<0.0001). The RDM of NFT-treated plants was 35% lower than the average of WPB
and WCC (Table 2,P<0.0001). Probably the high temperatures inside the greenhouse and from the
NFT NS might have accelerated the lettuce cultivation cycle, resulting in smaller plants than observed
in other studies with this crop (Helbel Junior et al., 2008).
The lettuce yields in WPB and WCC treatments did not differ statistically, but were 60% and 30%
higher than in NFT on a fresh and dry basis, respectively (Table 3,P<0.0001). Comparing with other
studies, ‘Vanda’lettuce yields in the present study were lower than those for ‘Isabella’(5.12 kg¢m
¡2
,
Martins et al., 2009)and‘Veronica’(5.77 kg¢m
¡2
, Faquin et al., 1996), but higher than the yield
obtained with the conventional soil system (1.1 kg¢m
¡2
, Grangeiro et al., 2006). The yield for treat-
ments with WPB (3.844 kg¢m
¡2
) and WCC (4.078 kg¢m
¡2
) were higher in this study than for the culti-
vars ‘Marisa’,‘Ver^
onica’,‘Veneza Roxa’and ‘Vera’used by Feltrim et al. (2009) (3.29 kg¢m
¡2
) and
‘Regina’and ‘Mimosa’by Andriolo et al. (2004) (3.1 kg¢m
¡2
), both using pine bark substrate, because
of the growth reduction caused by high temperatures in summer time.
Table 2. Root length, shoot diameter and height, root volume, number of leaves, leaf area, 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
Leaf
area
SFM SDM RFM RDM
(cm) (cm) (cm)
z
(mL) leaves (cm
2
)(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 xx. Means followed by different letters in the columns differ by Tukey’s test
according to the indicated probability (P). OBS.: NS Dnot significant at 5% probability in Tukey’s test.
158 R. S. FERRAREZI AND R. TESTEZLAF
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The shoot:root ratio differed among treatments, with WPB having the lowest values (Table 3,PD
0.0147). These results were similar to those obtained by Santos et al. (2010). The leaf water content was
comparable to that reported by Santos et al. (2010), which was about 8% lower in WCC compared
with other growing medias (Table 3,P<0.0001).
The NFT induced the lowest root length, shoot diameter and height, root volume, leaf area, shoot
(SFM) and root (RFM) fresh mass and shoot (SDM), root (RDM) dry mass (Table 2) and lower plant
yield (Table 3) at harvest compared with the lettuce grown in substrate, probably because of the high
temperature of the NS in contact with plant roots. Conversely, the lettuce grew exuberantly in the
WPB and WCC treatments (Table 3), showing salability and higher quality than NFT. Probably both
substrates provided an increase in the oxygen concentration at the root system due to the porous space
between particles, reducing the negative effects of the high NS temperatures. Unfortunately, this study
measured neither the temperature nor the oxygen content in the NS.
Shoot and root macro- and micronutrient concentrations
There were no visual symptoms of nutrient toxicity or deficiency in plants throughout the experimental
period, except for the salt accumulation in WPB, which induced typical edge-burn symptoms in older
leaves, probably caused by high EC in this substrate at the beginning of experiment.
The shoot macronutrient analysis indicated that N, Ca, and Mg concentrations were higher in the
WPB treatment and that P and K concentrations were lower in NFT compared with other substrates
(Table 4). The S concentration was 35% higher in NFT compared with WPB and WCC. These values
were similar to those observed by Martins et al. (2009) and Lopes et al. (2007) and were consistent
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).
Plant yield
Growing media Fresh basis (kg¢m
¡2
) Dry basis (kg¢m
¡2
) Shoot/root ratio Leaf water content (%)
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).
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
media
NPKCaMgSBCu
x
Fe Mn Zn
(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/xx.
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 Dnot
significant at 5% probability in Tukey’s test. VC Dvariation coefficient.
JOURNAL OF PLANT NUTRITION 159
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with the values recommended by Silva (1999) and Trani and Raij (1997), with the exception of Ca,
which was slightly below the recommended range (15 to 25 g¢kg
¡1
). The shoot macronutrient concen-
trations were lower in NFT compared with the plants grown in wick substrates, probably due to the
lower growth caused by the temperature of the NS (Table 4). Helbel Junior et al. (2008) cited that high
NS temperatures can induce plant root damage, causing reduction in the nutrients uptake and conse-
quently in the growth because of feed deficiency.
An analysis of the shoot micronutrient concentrations in lettuce revealed that WPB resulted in a B
concentration that was 29% lower than in the other treatments (Table 4). The Cu concentration in the
NFT treatment was 11.2 times greater than WPB and 5.5 times greater than WCC, and the Zn concen-
tration was 4.2 times higher in the NFT than the other substrates. The WCC treatment showed the
highest values for Fe, which was 39% higher than WPB and 24% than NFT (Table 4). There was no sig-
nificant difference among substrates for the shoot Mn concentration. The results were consistent with
those indicated by Silva (1999) and Trani and Raij (1997). However, the Cu and Zn values were higher
than the optimal level indicated by these authors.
The root macronutrient concentrations were 73% higher for N, 82% for P, 60% for K and 70% for S
in NFT compared with substrates (Table 4). However, the Ca and Mg concentrations were 41% and
58% higher, respectively, in WPB than in other treatments (Table 4).
The root micronutrient concentrations with NFT were higher for B (two times higher), Cu
(153 times higher), Fe (two times higher), and Zn (31 times higher) than with the other substrates
(Table 4). This result was most likely due to the incomplete removal of these elements during the sub-
strate washing procedures in the lab, accumulating more nutrients in the roots due to the direct contact
with NS. In contrast, lettuce roots grown with NFT had the lowest Mn concentration, with 28% higher
values in WCC and 48% higher in WPB (Table 4).
The results on nutrient concentrations in the plant tissues were not only associated with technical
characteristics of the tested wick systems and concomitant plant physiological implications, but also
rather to differences in the nutrient supplied in each treatment. Tap irrigation water was applied sev-
eral times in the wick irrigation system, which had a quite different composition than the NS, in order
to leach out salts as recommended by the manufacturer, while in the NFT system only applied NS was
applied. Thus, the performance of the wick irrigation treatments could have been biased by operations
that were not inherent to the system, but had to be performed to reduce substrate EC. The frequency
of tap water application is still unknown by growers.
Substrate macro- and micronutrient concentrations
The macronutrient concentrations differed between the two substrates (Figure 5). Compared to the ini-
tial nutrient levels in the substrates (Table 1), all nutrients increased with nutrient solution supply,
while pH decreased due to the acidifying characteristic of the NS used. In general, pH, EC, NO
3
-N, Ca,
Mg, and S were higher in WPB, while NH
4
-N, P, and K were higher in WCC (Figure 5).
Substrate concentrations of Mn and chloride were higher in WPB, while B, Cu, Fe, Zn, and sodium
were higher in WCC (Figure 5). There was a quadratic pattern of B, Fe and Zn concentrations, with a
reduction of concentrations in the final growth period probably by the increasing use by plants in this
phase. Consistently, there was an increase in the Fe concentration in the substrate over the experimen-
tal period, but concentrations were lower than recommended by Furlani (1998) and Furlani et al.
(1999). High concentrations of chloride and sodium were observed with both substrates, which were
reduced by leaching and tap water use instead of NS (Figure 5).
The increase in EC caused by the evaporation and salt accumulation increased the substrate macro
and micronutrient concentrations (Figure 5). This phenomenon is well described in the literature,
especially in the upper substrate layer (already cited in the pH and EC discussion section). Unfortu-
nately, the EC or the nutrient concentrations in layers was not measured, since the substrate thickness
was less than 6 cm, what made the layered measurements difficult. A decrease in EC and macronutrient
concentrations on the last growing day (DAT 29) was observed by the increased NS consumption from
high plant growth during this period (Figure 4), without reducing plant growth at the harvest. Both
160 R. S. FERRAREZI AND R. TESTEZLAF
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substrate leaching and tap water application in the tank instead of NS did not significantly reduce the
substrate micronutrient concentrations (Figure 5). Another possible way to reduce the substrate macro
and micronutrient concentrations to avoid plant damages would be the use of less concentrated NS
with a lower EC, as the evaporation concentrates the nutrients and increases the EC.
NS macro- and micronutrient concentrations
Weekly macronutrient concentrations of the NS varied according to the tank analyzed (Figure 6). NO
3
-
N, P, K, Ca, Mg, and S values were higher in the NFT tank, and the pH and NH
4
-N were higher in the
WPB and WCC tanks. The EC was similar in both NS used (Figure 6). The P concentrations shown in
Figure 6 were close to those recommended by Furlani (1998) and Furlani et al. (1999) for lettuce. Con-
centrations of S were 50% lower than recommended. There was a linear increase in the S concentration
in the WPB and WCC tanks over time (Figure 6).
There also were differences in weekly micronutrient concentrations in the NS among tanks
(Figure 6). Cu and Zn concentrations were higher in the NFT tank, while the values of Fe, bicarbonate
and chloride were higher in the WPB and WCC tanks. All the micronutrient results presented in
Figure 6 were close to the values recommended by Furlani (1998) and Furlani et al. (1999) for lettuce,
with the exception of Fe, which showed a value 30% lower than recommended. There was a linear
increase in Cu concentration over time in the NFT tank and a quadratic trend over time in Fe in the
WPB and WCC tanks (Figure 6).
Bicarbonate concentration was lower in the NFT treatment on DAT 15 and 22, returning to the ini-
tial values of original water concentration at 29 DAT (Figure 6). In general, this concentration was
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).
JOURNAL OF PLANT NUTRITION 161
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similar to the amounts supplied by the tap water. Chloride was 7–8 times greater than the initial water
concentration, and sodium was almost twice as much as was initially present in the water (Figure 6).
Bicarbonate, chloride and sodium present in this experiment are within the acceptable limits indicated
by Furlani (1998) and Furlani et al. (1999) and did not cause any damage to plants.
The NS macro and micronutrients concentration were determined prior to the replacement, and
showed a significant increase in S, Cu, Fe, Mn, Zn, and Na over time, probably caused by the reduction
of plant uptake as an effect of the higher temperature of NS in NFT or yet by a higher supply than
needed (Figure 6).
Conclusions
The wick irrigation system with self-compensating troughs, irrespective of substrate, showed higher let-
tuce yield than the NFT system. However, the EC in WCC was more stable than in WPB, facilitating
nutritional management during the crop cycle without causing salinity damage to the plants. Wick irri-
gation systems resulted in lettuce salable plants, being an alternative for regions with high temperatures
because of the substrate cooling effect, limited manpower and electrical power. The obtained biometric
results did not prove a technical superiority of the wick irrigation system over NFT, but merely indi-
cated that, under the specific conditions applied in this experiment, the NFT system performed poorly.
Further investigations should be conducted in different seasons and with other cultivars, trying to
establish the water and nutrient management guidelines suitable for different substrates to improve the
utilization of this technology.
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 replica-
tions §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).
162 R. S. FERRAREZI AND R. TESTEZLAF
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Acknowledgments
We thank Dr. Fl
avio Bussmeyer Arruda, Antonio Carlos Ferreira Filho, Maur
ıcio Madoglio Sultani, Renato Traldi Sal-
gado and Vicente Dias Martarello for the technical collaboration, Dr. Marc W. van Iersel for reviewing the manuscript
and the constructive criticism, Antonio Carlos Ferreira Filho for making the figures using Google Sketchup, the Board of
Directors of the School of Agricultural Engineering for donating the material for the assembly of the experimental plots,
and the Hidrogood Horticultura Moderna Company for donating the self-compensating troughs.
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.
Funding
The National Council of Technological and Scientific Development (Ministry of Science and Technology, Brazil) pro-
vided a PhD scholarship to the first author. Funding for this research was provided through the PRP/FAEPEX/UNI-
CAMP (award no 261/10).
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