Endive production under different hydroponic systems and electrical conductivities of the nutrient solution¹

Produção de chicória em diferentes sistemas hidropônicos e valores de condutividade elétrica da solução nutritiva

ABSTRACT

Soilless cultivation can be performed using different hydroponic systems, and each system has its own particularities and adaptation according to the crop and environmental conditions. The aim of this study was to evaluate the production of endive grown in hydroponic systems and subjected to different electrical conductivities of the nutrient solution. The research was conducted in a greenhouse, adopting a split-plot design, with the plots represented by the hydroponic systems (nutrient film technique (NFT), semi-hydroponic (SH) and deep flow technique (DFT)), and the subplots by electrical conductivities (2.90 and 1.6 dS m^-1). The following variables were evaluated: stem diameter, plant height, number of leaves, leaf area, shoot fresh mass, root fresh mass, total fresh mass, shoot dry mass, root dry mass, total dry mass, leaf succulence and specific leaf area. The semi-hydroponic system promotes greater development of endive regardless of the concentration of the nutrient solution. Nutrient solutions with an EC of 1.6 dS m^-1 are recommended for the SH and DFT systems, and nutrient solutions with an EC of 2.9 dS m^-1 are recommended for the NFT system.

Key words:
Cichorium endivia L.; soilless cultivation; NFT system; DFT system; semi-hydroponic

HIGHLIGHTS:

Endive plants’ growth is influenced by cultivation systems.

The semi-hydroponic system provides better environmental conditions for plants.

Increasing EC increases succulence in the NFT system, but it is reduced in the DFT system.

RESUMO

O cultivo sem solo pode ser realizado utilizando diferentes sistemas hidropônicos, sendo que cada sistema apresenta suas particularidades e adaptação conforme a cultura e as condições ambientais. O objetivo deste trabalho foi avaliar a produção de chicória cultivada em sistemas hidropônicos e submetida a diferentes valores de condutividade elétrica da solução nutritiva. A pesquisa foi conduzida em casa de vegetação, adotando-se o delineamento em parcelas subdivididas, sendo as parcelas representadas pelos sistemas hidropônicos (técnica de filme de nutrientes (NFT), semi-hidropônico (SH) e técnica de fluxo profundo (DFT)), e as subparcelas pelos valores de condutividade elétrica (2,90 e 1,6 dS m^-1). Foram avaliadas as seguintes variáveis: diâmetro do caule, altura da planta, número de folhas, área foliar, massa fresca da parte aérea, massa fresca da raiz, massa fresca total, massa seca da parte aérea, massa seca da raiz, massa seca total, suculência foliar e área foliar específica. O sistema semi-hidropônico proporciona maior desenvolvimento da escarola independentemente da concentração da solução nutritiva. Recomenda-se soluções nutritiva com CE de 1,6 dS m^-1 para os sistemas SH e DFT, e CE de 2,9 dS m^-1 para o sistema NFT.

Palavras-chave:
Cichorium endivia L.; cultivo sem solo; sistema NFT; sistema DFT; semi-hidropônico

Introduction

Endive (Cichorium endivia L.) is a vegetable of the Asteraceae family, whose leaves are rich in bioactive compounds with antidiabetic, immunomodulatory, and antioxidant functions, in addition to promoting good digestion and reducing the risk of gastrointestinal diseases (Perović et al., 2021; Pouille et al., 2022; Moscatello et al., 2023).

Although it is mainly grown under open-air conditions, endive has the potential to be produced hydroponically. In hydroponic cultivation, essential nutrients are supplied via nutrient solution, using salts with a higher degree of purity and solubility (Velazquez-Gonzalez et al., 2022). This cultivation system makes it possible to significantly increase overall agricultural production using minimum resources, especially cultivation space and water consumption (Chowdhury et al., 2024).

Among the main existing hydroponic cultivation systems, the systems in which plants are grown in a liquid medium using an aqueous solution stand out (nutrient film technique (NFT) and deep flow technique (DFT)), and there are also systems using solid media, in which plants are grown in substrates housed in containers and fertigated by drip irrigation, also called semi-hydroponic (SH) (Nunes et al., 2020; Sausen et al., 2020; Chowdhury et al., 2024; Góis et al., 2024; Oliveira et al., 2024).

In Brazil, the NFT system is the most widely adopted in the cultivation of leafy vegetables, being used by around 90% of producers (Oliveira et al., 2024). However, studies have been conducted testing other hydroponic systems, such as Góis et al. (2024) working with lettuce, and Oliveira et al. (2024) working with pak choi, in the NFT, DFT and SH systems, which showed that the SH system provides greater plant growth. Furthermore, these authors observed that plants grown in the SH system showed a positive and linear response to the increase in electrical conductivity (EC) of the nutrient solution, while in the NFT system the plants showed less tolerance to EC. Each system has its own peculiarities, in such a way that they provide different conditions for the development of the root system and can consequently affect the development and productivity of plants.

Yang et al. (2024), working with lettuce crop grown in two hydroponic systems (NFT and DFT), observed that the NFT system promoted higher yield, but more severe tip burn symptoms than DFT. In addition, these authors found that the DFT system promoted higher concentrations of antioxidants (vitamin C, total carotenoids, non-acidified phenols and total chlorophyll) than NFT.

In a study with endive, the NFT and DFT systems using brackish water to prepare the nutrient solution, Silva et al. (2020) observed no difference between the systems under conditions without salt stress (electrical conductivity of 0.34 dS m^-1). However, these authors observed that, under saline conditions with NaCl concentration of up to 3.0 dS m^-1, it can be used in endive cultivation in the DFT system.

These studies show that crops perform differently in terms of water and nutrient uptake depending on the hydroponic system used. Therefore, fertilizer recommendations may need to be adjusted to suit these conditions in order to avoid excessive use of nutrients and water (Yang et al., 2024). According to Wibisono & Kristyawan (2021), for plants to express their full production potential, it is necessary to promote the correct balance of water, oxygen and minerals. This balance can be achieved with effective management of the nutrient solution and the appropriate selection of the hydroponic system.

The aim of this study was to evaluate the production of endive grown in hydroponic systems and subjected to different electrical conductivities of the nutrient solution.

Material and Methods

The research was conducted in a protected environment, from March to April 2020, at Universidade Federal Rural do Semi-Árido, in Mossoró (UFERSA), RN, Brazil (5^o 12’ 48’’ S, 37^o 18’ 44’’ W, and 18 m of altitude). The greenhouse used has the following dimensions: 18 × 7 × 3.5 m, for length, width and ceiling height, respectively. The structure has an arched roof, in galvanized steel, and a covering with low-density polyethylene film (150 microns) and lateral screens with black-colored 50% shade net.

During the experiment, climate data of maximum (Tmax), average (Tavg) and minimum (Tmin) temperatures (ºC), as well as maximum (RHmax), average (RHavg) and minimum (RHMin) relative humidity (%), were collected using an automatic meteorological station (Campbell Scientific, model CR1000), installed inside the greenhouse. Variations from 27.99 to 38.14 ºC were observed for Tmax; 27.28 to 31.96 ºC for Tavg; 20.82 to 28.29 ºC for Tmim. For RH, the variations were from 56.17 to 100% for RHmax, 48.16 to 88.63 for RHavg and 22.89 to 78.96% for RHmin.

The experiment was conducted in split plots, with the plots represented by three hydroponic systems (nutrient film technique (NFT), semi-hydroponic (SH) and deep flow technique (DFT)), and subplots by two electrical conductivities of the nutrient solution (1.61 and 2.90 dS m^-1). In all hydroponic systems, four replicates were used, with each experimental plot consisting of five plants.

The different conductivities were obtained from different concentrations of nutrient solution [50% (1.61 dS m^-1) and 100% (2.90 dS m^-1)], based on the macronutrient concentration recommended by Furlani et al. (1999) for the hydroponic cultivation of leafy vegetables, with the following fertilizer concentrations, in g 1000L^-1: 750 g of calcium nitrate (15% of N and 20% of CaO); 500 g of potassium nitrate (13% of N and 43% of K₂O); 150 g of monoammonium phosphate (11% of N and 61% of P₂O₅); 400 g of magnesium sulfate (10% of Mg and 17% of S). For micronutrients, the commercial products Dripsol Micro Rexene Equilíbrio and Dripsol Micro Ferro Q48 (Iron chelate Q48 EDDHA 6%, Dripsol SQM Vitas^®) were used at a dose of 30 g 1000L^-1 for the standard nutrient solution (100%).

The preparation of the nutritional solution used water collected from the UFERSA supply system, with the following chemical characterization: pH = 7.55; EC = 0.56 dS m^-1, Ca²⁺ = 0.85 mmol_c L^-1, Mg²⁺ = 1.22 mmol_c L^-1, K⁺ = 0.35 mmol_c L^-1, Na⁺ = 3.82 mmol_c L^-1, Cl^- = 2.45 mmol_c L^-1, HCO₃ ^- = 3.15 mmol_c L^-1, CO₃ ^2- = 0.55 mmol_c L^-1, and Sodium adsorption ratio (SAR) = 3.09 (mmol L^-1)^0.5. To adjust the pH of the nutrient solutions to 6.0 (±0.5), 0.1 M HCl or 0.1 M NaOH solutions were applied.

The experiment was carried out using endive seedlings (Cichorium endivia L., cv. Gigante Barbarella), produced in expanded polystyrene trays with 200 cells, using coconut fiber substrate. Four seeds were sown in each cell, at a depth of 0.05 m. After the fifth day of emergence (DAE), thinning was carried out, leaving the most vigorous seedling in each cell. Fertigation began after thinning using the floating system with the nutrient solution (Furlani et al., 1999) diluted to 50%. Transplanting of the seedlings was carried out when the seedlings had 4-5 definitive leaves, using five plants per plot of the hydroponic systems. The same structures and management used by Góis et al. (2024) in research carried out with lettuce crop were used.

The NFT had six benches, each bench representing a plot, composed of four hydroponic profiles measuring 2.0 m in length and containing seven holes, spaced 0.25 m apart. The two central profiles were considered as the observation plot, discarding the two plants at the ends of these profiles, so that 10 plants were evaluated in each plot. The benches were built from sawn wood, with a 5% slope, spacing of 0.20 m between profiles and 0.60 m between benches.

Nutrient solution circulation was controlled using an analog timer, adopting a 15-minute circulation schedule interspersed every 15 minutes from 5:00 a.m. to 6:00 p.m. During the night, the interval between circulations was two hours, with each event lasting 15 minutes (Martinez, 2021).

The SH system was composed of plastic trays with dimensions of 0.37 × 0.60 × 0.14 m (width, length, and height, respectively), with a capacity of 20 L, filled with 18 L of substrate. The trays were distributed on a 0.6 m high sawn wood bench, spaced 0.10 m apart.

The substrate used was composed of coconut fiber (Gold Mix granulated - Amafibra^®); with EC = 0.3 dS m^-1, high water retention capacity (50.7%), total porosity of 95%, density of 150 kg m^-3 and washed sand (2:1 (v/v)).

Each plot was represented by a tray containing five plants, four of which were distributed at the ends (keeping a space of 0.10 m between the plant and the edge of the tray) and one in the center.

The trays contained drainage systems consisting of a valve and a layer of gravel (0.02 m) covered by a textile blanket. The system worked in a closed manner, with the nutrient solution collected by a system composed of PVC pipes and connections (40 mm). During the day, six fertigation events were carried out, the first at 6 a.m., and the others at 2-hour intervals and each event lasting 1.0 minute from transplanting to 15 days after and 2.0 minutes from 16^th to harvest (Pessoa et al., 2023).

For the Deep Film Technique (DFT) system, plastic trays similar to those of the SH system were used. An expanded polystyrene plate (0.01 × 0.35 and 0.58 m, for thickness, width and length, respectively) was placed in each tray. Similar to the scheme adopted in the SH system, each tray represented an experimental unit and contained five plants. Each plate was perforated with five holes (0.03 cm in diameter), which were used to fix expanded polystyrene cups (50 mL), containing holes in their base to allow for root system growth and absorption of nutrient solution (Martinez, 2021).

During the experiment, a layer of nutrient solution was maintained with depth of 0.12 m, which was regulated by an overflow constructed with pipe and connections (20 mm). The nutrient solution was automatically recirculated using a motor pump set, which was controlled by a digital timer, being activated at 2-hour intervals and lasting 10 minutes each event. In addition to circulating the nutrient solution, an air compressor (ACO -008 120W 220v, flow rate of 100 L min^-1) was used, to which microtubes (0.20 m long and 5.0 mm internal diameter) were attached to distribute oxygen inside the trays.

In all systems, the nutrient solutions were monitored and controlled daily, replacing the volume of water required by the plants. The nutrient solution was replaced whenever a 10% reduction in initial electrical conductivity was detected (Góis et al., 2024).

Harvest was performed 40 days after transplanting, and the plants were then analyzed for the following variables: plant height (PH), number of leaves (NL), leaf area (LA), shoot fresh mass (SFM), root fresh mass (RFM), total fresh mass (TFM), shoot dry mass (SDM), root dry mass (RDM), total dry mass (TDM), leaf succulence (LS) and specific leaf area (SLA).

PH was measured using a graduated ruler, considering the distance between the plant collar and the apex of the largest leaf (Benincasa, 2004).

NL was determined manually, considering the leaves that had a leaf blade greater than 0.03 m and with more than 70% green color. Dry and/or yellowed leaves were not counted.

LA was calculated using the leaf disc methodology (Souza et al., 2012). Twenty leaf discs (4.9 cm²) were collected from each plot. The samples, discs and leaves were then placed in paper bags and dehydrated in a forced air circulation oven at 65 ºC until they reached constant weight. LA was determined according to Eq. 1:

$$LA=\frac{DA\times LDM}{{\displaystyle \frac{DDM}{ND}}}$$ (1)

where:

LA - leaf area, cm² per plant;

DA - leaf disc area, cm²;

LDM - leaf dry mass, g;

DDM - leaf disc dry mass, g; and,

ND - number of discs used in the plot.

SFM, RFM and TFM were measured immediately after harvest, considering the average mass of 10 plants, on a precision digital scale (0.01 g).

To quantify SDM, RDM and TDM, plants were placed in previously identified paper bags, dried in a forced air circulation oven, at temperature of 65 ºC, until reaching a constant weight and then weighed on a precision digital scale (0.01 g).

LS was determined according to Mantovani (1999), considering the ratio between the water content in the leaf blade and the leaf area of the plants, Eq. 2:

$$LS=\frac{LFM-LDM}{LA}$$ (2)

where:

LS - leaf succulence, g H₂O cm^-2;

LFM - leaf fresh mass, g;

LDM - leaf dry mass, g; and.

LA - leaf area, cm² per plant.

SLA was determined according to Benincasa (2004), considering the ratio between LA and LDM, Eq. 3:

$$SLA=\frac{LA}{LDM}$$ (3)

where:

SLA - specific leaf area, cm² g^-1;

LA - leaf area, cm²; and,

LDM - leaf dry mass, g.

The data obtained were subjected to ANOVA using the F test (p ≤ 0.05 and p ≤ 0.01). The decomposition was performed when a significant interaction was detected between the studied factors. The effect of the applied treatments was analyzed using the means comparison test (Tukey, p ≤ 0.05). The statistical software Sisvar 5.3 (Ferreira, 2019) was used for the statistical analyses.

Results and Discussion

The hydroponic systems (HS) affected the variables plant height (PH) and number of leaves (NL) at 0.05 probability level, as well as the variables leaf area (LA), shoot fresh mass (SFM), root fresh mass (RFM) and total fresh mass (TFM) at 0.01 probability level. There was no significant response (p > 0.05) for plant height and stem diameter (SD) (Table 1).

Table 1
Summary of the analysis of variance and mean values for plant height (PH), number of leaves (NL), stem diameter (SD), leaf area (LA), shoot fresh mass (SFM), root fresh mass (RFM), total fresh mass (TFM) of endive subjected to different electrical conductivities of the nutrient solution and different hydroponic systems

SV	DF	Mean squares
		PH	NL	SD	LA	SFM	RFM	TFM
Block	3	0.26 ns	59.73 ns	0.83 ns	327113.34 ns	74.38 ns	50.24 ns	45.29 ns
HS	2	34.25*	228.55*	1.50 ns	18584695.89**	10626.98**	341.89*	14569.74**
Error 1	6	3.33	25.98	1.61	223568.89	321.68	40.41	213.23
EC	1	15.04 ns	98.62 ns	3.06 ns	13459.71 ns	873.02 ns	238.39 ns	2023.27 ns
HS × EC	2	15.87 ns	65.57 ns	2.27 ns	3429849.38 ns	2620.82 ns	126.71 ns	3502.11 ns
Error 2	9	21.70	47.58	1.05	1099139.49	2553.66	157.24	3500.39
		Test of means
		PH (cm)	NL (unit)	SD (mm)	LA (cm2 plant-1)	SFM	RFM	TFM
						(g plant-1)
Hydroponic systems
NFT		21.58 b	30.50 b	9.84 a	2356.71 c	154.61 b	35.21 b	189.81 b
SH		25.37 a	40.42 a	10.67 a	5313.31 a	215.71 a	47.89 a	263.61 a
DFT		24.91 a	32.00 b	10.09 a	3192.25 b	150.74 a	38.84 ab	189.57 b
Electrical conductivity
1.6 dS m-1		24.75 a	36.33 a	10.55 a	3644.44 a	179.72 a	43.79 a	223.51 a
2.9 dS m-1		23.17 a	32.28 a	9.83 a	3597.07 a	167.65 a	37.49 a	205.15 a
CV 1 (%)		7.61	14.86	10.58	13.06	10.33	15.64	6.81
CV 2 (%)		19.44	20.11	10.03	28.92	18.12	20.85	17.60

• SV - Source of variations, CV - Coefficient of variation, HS - Hydroponic systems, EC - Electrical conductivity, ns - Non-significant; * - Significant at p ≤ 0.05; ** - Significant at p ≤ 0.01

The SH and DFT systems promoted higher values for PH. For the other variables, the SH system promoted higher values for LA, SFM, RFM and TFM. Compared with the means of the other systems, the values obtained in the SH system were 29.3, 91.5, 41.3, 29.3, and 38.9% higher for LA, SFM, RFM and TFM, respectively (Table 1).

The greater superiority of the SH system over other hydroponic systems occurs because the SH promotes greater water and thermal balance in the root system zone, favoring the absorption of water and nutrients. This greater balance provides better conditions for plant development. These results corroborate those presented by other authors, for example Góis et al. (2024) and Oliveira et al. (2024), who, working with lettuce and pak choi crops, respectively, obtained greater production in plants grown in the SH system.

As shown in Table 1, the EC did not affect any of these variables, which obtained mean values of 23.96 cm (PH), 34.30 leaves (NL), 10.19 mm (SD), 3620.75 cm² per plant (LA), 173.68 g per plant (SFM), 40.64 g per plant (RFM) and 214.33 g per plant (TFM) (Table 1).

These results show that, under the conditions of the site where this study was conducted, endive cultivation in different hydroponic systems can be carried out with a nutrient solution diluted by 50% without any loss in plant yield, confirming the results observed by Luz et al. (2009), allowing savings in the use of fertilizers.

The interaction between hydroponics systems (HS) and electrical conductivity (EC) significantly affected (p ≤ 0.01) shoot dry mass (SDM). In addition, it significantly affected (p ≤ 0.05) total dry mass (TDM) and leaf succulence (LS), but did not significantly affect (p > 0.05) root dry mass (RDM) and specific leaf area (SLA). The variables RDM and SLA were affected (p ≤ 0.05) by HS (Table 2).

Table 2
Summary of the ANOVA for shoot dry mass (SDM), root dry mass (RDM), total dry mass (TDM), leaf succulence (LS) and specific leaf area (SLA) of endive subjected to different electrical conductivities of the nutrient solution and different hydroponic systems

SV	DF	Mean squares
		SDM	RDM	TDM	LS	SLA
Block	3	6.42 ns	3.46 ns	19.02 ns	26.91 ns	35249.97 ns
HS	2	23.35 ns	17.99*	7.15 ns	235.91 ns	127580.98*
Error 1	6	12.85	2.78	25.75	74.22	24757.98
CE	1	2.55 ns	1.17 ns	7.57 ns	152.16 ns	35494.73 ns
HS × CE	2	12.05**	0.56 ns	11.05*	320.39*	1387.42 ns
Error 2	9	1.13	0.94	2.61	68.53	28523.80
CV 1 (%)		21.33	24.25	18.43	14.37	23.04
CV 2 (%)		10.44	16.29	11.23	13.81	20.19

• SV - Source of variations, CV - Coefficient of variation, ns - Non-significant; * - Significant at p ≤ 0.05; ** - Significant at p ≤ 0.01.

SDM was affected by the cultivation systems according to the analyzed EC. The SH system promoted higher SDM (12.46 g per plant) at EC of 1.6 dS m^-1 and lowest in DFT system at EC of 2.9 dS m^-1 (7.04 g per plant). NFT did not differ from SH at the highest EC, indicating that endive may be more nutritionally demanding in NFT. Furthermore, it was found that EC of 2.9 dS m^-1 promoted greater SDM in the SH system, with no effect of EC on plants grown in the NFT system. On the other hand, in the DFT system, the highest values occurred at EC of 1.6 dS m^-1. There was no effect of EC on SDM in the SH system (Figure 1A).

Figure 1
Shoot dry mass (SDM - A), root dry mass (RDM - B) and total dry mass (TDM - C) of endive subjected to different electrical conductivities of the nutrient solution and different hydroponic systems

The increase in the EC of the nutrient solution increased the SDM of plants grown in the NFT system by 18.3% but reduced it in the DFT system by 30.8% (Figure 1A). This result indicates that the plants were more sensitive to the increase in EC in the DFT system, confirming the observations made by Góis et al. (2024) and Oliveira et al. (2024).

These results corroborate those presented by other authors, for instance in studies conducted with parsley (Nunes et al., 2020), Greek sweet onion (Mouroutoglou et al., 2021), lettuce (Góis et al., 2024) and pak choi (Oliveira et al., 2024), also reported greater development of the aerial part in plants grown in semi-hydroponic system.

A nutrient solution with a very high EC causes an osmotic effect, making it difficult for plants to absorb water. Under these conditions, plants adopt a strategy to adapt to unfavorable conditions by seeking to reduce water loss through transpiration, resulting in morphological and anatomical changes, which leads to reduced development of the aerial part (Li et al., 2023).

The DFT system promoted greater RDM accumulation (5.42 g per plant), being superior to the other systems by 104.5% (NFT) and 78.3% (SH) (Figure 1B). This superiority of DFT over the others occurs because in this system the roots are fully submerged in nutrient solution throughout the growth process (Chowdhury et al., 2024). In a comparison of DFT with NFT, although NFT can provide oxygen to crops by exposing the root tips to air, the air compressor installed in DFT increases dissolved oxygen levels in the solution (Yang et al., 2024).

TDM differed between the cultivation systems only at the EC of 1.6 dS m^-1, with the highest values occurring in the SH (16.24 g per plant) and DFT (15.84 g per plant) systems, being 26.9 and 23.7% higher, compared to the NFT system (12.80 g per plant). Furthermore, there was an effect of EC on TDM only in plants grown in the DFT system, in which the increase in EC caused a 19.9% loss in TDM (Figure 1C).

The NFT system caused lower TDM possibly because the irrigations were interspersed with intervals without availability of nutrient solution. Thus, the reduction in plant growth may have been due to the occurrence of water and/or osmotic stresses (Rodríguez-Ortega et al., 2019).

The hydroponic systems differed in terms of LS only at higher EC, with the highest value obtained in the NFT system, being 41.5% higher compared to the value obtained in the SH system. LS was affected by EC in the NFT and DFT systems, in which the highest EC caused increases of 22.1 and 21.6% for NFT and DFT, respectively (Figure 2A).

Figure 2
Leaf succulence (A) and specific leaf area (B) of endive subjected to different electrical conductivities of the nutrient solution and different hydroponic systems

The increase in LS in response to the increase in EC for NFT and DFT systems was also observed by other authors working with leafy vegetables, such as arugula (Cordeiro et al., 2019), endive (Oliveira et al., 2023), lettuce (Pessoa et al., 2023) and pak choi (Oliveira et al., 2024).

Under salt stress, either by adding NaCl or by excessive nutrients in the nutrient solution, plants seek alternatives to perform osmotic adjustment, regulating ionic concentration in leaf tissues. Thus, the increase in leaf succulence increases the tolerance of plants to salt stress, increasing the efficiency in water use by plants (Lim et al., 2020).

Still regarding Figure 2A, there was no effect of EC on LS in plants grown in SH. Cultivation in substrate provides better environmental conditions for the root system of plants, favoring their growth (Oliveira et al., 2024).

The SH and DFT systems promoted higher values for SLA, which were 96.6 and 102.1% higher, respectively, compared to the SLA obtained in the NFT system (Figure 2B). The decrease in SLA in plants grown in the NFT system may be an indication that in this system the increase in EC caused salt stress (Yao et al., 2023).

According to Shen et al. (2022), the increase in palisade tissue thickness can promote the synthesis of organic matter to maintain normal plant metabolism, thus reducing the damage caused by salt stress. Plants with higher SLA can produce more leaf biomass to maximize carbon gain per unit of leaf mass in environments with more efficient use of available resources (Gao et al., 2022).

Conclusions

1. The semi-hydroponic system promotes greater development of endive regardless the concentration of the nutrient solution.

2. Nutrient solutions with an EC of 1.6 dS m^-1 are recommended for the SH and DFT systems, and nutrient solutions with an EC of 2.9 dS m^-1 are recommended for the NFT system.

Acknowledgments

Thanks to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for granting a scholarship to the 5^th, 7^th, 8^th and 9^th authors.

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• ¹ Research developed at Universidade Federal Rural do Semi-Árido, Mossoró, RN, Brazil

Supplementary documents

• There are no supplementary sources.

Financing statement

• This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Funding Code 001.

Edited by

• Editors: Ítalo Herbet Lucena Cavalcante & Hans Raj Gheyi

Data availability

There are no supplementary sources.

Publication Dates

• Publication in this collection
  10 Mar 2025
• Date of issue
  July 2025

History

• Received
  15 Oct 2024
• Accepted
  27 Jan 2025
• Published
  30 Jan 2025