Arugula and jambu intercropping with controlled irrigation increases land use efficiency under semi-arid conditions¹

Consórcio de rúcula e jambu com irrigação controlada aumenta a eficiência no uso da terra em condições semiáridas

ABSTRACT

The objective of this study was to evaluate the production characteristics and the efficiency of land and water use in monoculture and intercropping of arugula with jambu under water regimes in two crop cycles in the semi-arid region of Ceará, Brazil. The experimental design was randomized blocks, in a split-plot scheme, with 20 treatments and four replicates. The plots were irrigation, corresponding to 50, 75, 100, 125 and 150% of ETc. The subplots were the intercropping and single systems. In each cycle, the growth characteristics of the plants and the efficiency of water and land use were evaluated. The highest values were obtained for number of leaves, height, and fresh and dry mass of aerial parts and roots of arugula plants when intercropped. The best results for the growth variables of jambu were obtained for plants grown in monoculture. The productivity values were higher in the single-cropping system; however, the average land use efficiency values in the intercropped system were 1.23 and 1.28 in 2018 and 2019, respectively. The best results were obtained with 75% ETc (DI75) for arugula and full irrigation with 100% ETc (TI100) and excess irrigation with 125% ETc (EI125) for jambu. Water use efficiency was higher in the single system. The productivity indices obtained with the arugula-jambu intercropped system and DI75 confirm the higher biological efficiency. Based on the above, it is concluded that arugula and jambu are promising for intercropping under semi-arid conditions.

Key words:
Acmella oleracea (L.) RK Jansen; Eruca sativa Mill; intercropping; irrigation depths

HIGHLIGHTS:

Intercropping results in the highest land use efficiency, thus greater biological efficiency.

Jambu can be grown in association with arugula or alone using the crop coefficient (Kc) of arugula.

The yield of arugula under deficit irrigation with 75% of ETc tolerated 25% reduction in water used in its cultivation.

RESUMO

O objetivo deste trabalho foi avaliar as características produtivas e a eficiência do uso da terra e da água em monocultivo e consórcio de rúcula com jambu sob regimes hídricos em dois ciclos de cultivo em região semiárida do Ceará. O delineamento experimental foi em blocos casualizados, em esquema de parcelas subdivididas, com 20 tratamentos e quatro repetições. As parcelas foram as irrigações, com 50, 75, 100, 125 e 150% de ETc. As subparcelas foram os sistemas consorciado e solteiro. Em cada ciclo foram avaliadas as características de crescimento das plantas e a eficiência do uso da água e da terra. Os maiores valores foram obtidos para número de folhas, altura, e massa fresca e seca das partes aéreas e raízes das plantas de rúcula quando consorciadas. Os melhores resultados para as variáveis ​​de crescimento do jambu foram obtidos para as plantas cultivadas em monocultivo. Os valores de produtividade foram maiores no sistema solteiro; entretanto, os valores médios de eficiência do uso da terra no sistema consorciado foram de 1,23 e 1,28 em 2018 e 2019, respectivamente. Os melhores resultados foram obtidos com 75% ETc (DI75) para rúcula e irrigação total com 100% ETc (TI100) e irrigação em excesso com 125% ETc (EI125) para jambu. A eficiência do uso da água foi maior no sistema solteiro. Os índices de produtividade obtidos com o sistema consorciado rúcula-jambu e DI75 confirmam a maior eficiência biológica. Com base no exposto, conclui-se que rúcula e jambu são promissores para o consórcio em condições semiáridas.

Palavras-chave:
Acmella oleracea (L.) RK Jansen; Eruca sativa Mill; consorciação; lâmina de irrigação

Introduction

With population growth, the need for food production is expected to increase significantly in the coming decades (Campos et al., 2019). In general, agriculture is the sector that consumes the most high-quality water in the world, i.e., approximately 70% of global consumption (Ingrao et al., 2023).

Among the production systems that can contribute to increasing food production is intercropping. This practice consists of cultivating two or more cycles and/or species, simultaneously, in the same area (Mousavi & Eskandari, 2011). Compared to monoculture, the main advantage of intercropping is the better use of natural resources in ecosystems with limited resources (Mota et al., 2010). Intercropping can maintain or improve soil quality (Li et al., 2007; Zhang et al., 2016), promote greater biodiversity (Li et al., 2014; Brooker et al., 2015), reduce the incidence of invasive species (Rao et al., 2002), minimize the occurrence of pests and diseases (Ning et al., 2017), and reduce soil erosion and surface water runoff (Keesstra et al., 2018). This is because better efficiency in the use of environmental resources and adequate management of water and land are essential for the sustainability of agricultural production (Xinchun et al., 2017).

Arugula (Eruca sativa Mill) has been used as an intercrop among other vegetables, mainly because it has a short cycle and good adaptation to intercropping (Başer, 2016). Jambu (Acmella oleracea (L.) R. K. Jansen) is an herbaceous, annual vegetable, widely cultivated in the Brazilian Amazon region. In cooking, jambu provides a characteristic flavour and taste mainly due to the tingling sensation in the mouth and momentary anaesthetic effect, which attracts its consumers and connoisseurs in various regions of Brazil and the world (Gusmão & Gusmão, 2013; Santos & Gentil, 2015). The active compound, spilanthol, is responsible for the sensations mentioned by consumers of the crop, being present in all the tissues that make it up (Prachayasittukal et al., 2013).

Although studies on jambu intercropping are scarce, the crop has important characteristics for integrating intercropping systems, as its plants are small in size and have a short cycle (Borges et al., 2013). Another point to consider is that the increase in demand for the crop, due to its wide use, considerably expanded its cultivation in other regions of the country, which made it attractive even in semi-arid regions of Brazil, but when it is adequately irrigated (Gusmão & Gusmão, 2013).

Therefore, although some studies have indicated efficiency in the use of water (WUE) in intercropping systems (Gao et al., 2009; Ren et al., 2016; Koocheke et al., 2019), their evaluations, in general, are conducted only using full irrigation, and there are few studies that combine intercropping with deficit irrigation in semi-arid regions.

Within this context, the objective of this study was to evaluate the production characteristics and the efficiency of land and water use in a monoculture and in an intercropping system of arugula with jambu under water regimes in a semiarid region of Ceará, Brazil.

Material and Methods

The study was conducted from September to November 2018 and 2019 at the Vale do Curu Experimental Farm (FEVC), belonging to the Universidade Federal do Ceará (UFC), located in the municipality of Pentecoste, semi-arid region of the state of Ceará, Brazil, with geographic coordinates 3° 48’ 35.86” S and 39° 19’ 31.55” W at 34 m in altitude. According to Köppen’s classification, the climate is BSh (hot and semiarid, with irregular rainfall). The average relative humidity and average air temperature were 60% and 30 ºC in 2018 and 60% and 31 ºC in 2019, respectively.

The physicochemical characteristics of the soil at a depth of 20 cm were: P - 0.36 cmol_c dm^-3; K⁺ - 1.18 cmol_c dm^-3; Ca²⁺ - 6.86 cmol_c dm^-3; Mg²⁺ - 3.51 cmol_c dm^-3; Fe - 0.29 cmol_c dm^-3; Cu - 0.0014 cmol_c dm^-3; B - 0.005 cmol_c dm^-3; Zn - 0.008 cmol_c dm^-3; Mn - 0.28 cmol_c dm^-3; Al³⁺ - 0.0 cmol_c dm^-3; H⁺ + Al³⁺ - 0.99 cmol_c dm^-3; SB (sum of bases) - 11.55 cmol_c dm^-3; cation exchange capacity (CEC) (t) - 11.55 cmol_c dm^-3; CEC (T) - 12.54 cmolc dm^-3; organic matter (OM) - 3.9 dag kg^-1; pH - 7.2; V - 92.1%; m - 0.0%; electrical conductivity (EC) - 0.16 dS m^-1; coarse sand - 20 g kg^-1; fine sand - 515 g kg^-1; silt - 141 g kg^-1; clay - 164 g kg^-1; natural clay - 131 g kg^-1, texture - sandy; field capacity - 0.361 (cm³ cm^-³); permanent wilting point - 0.0545 (cm³ cm^-³); hydraulic conductivity of saturated soil - 9.5 (mm h^-1), and bulk density - 1.32 (g cm^-³).

The water used for irrigation in both years was classified as C3S1 (Richards, 2012), having, on average, the following quality characteristics: pH - 6.80; EC - 0.75 dS m^-1; Sodium Adsorption Ratio (SAR) - 1.60; Ca²⁺ - 2.0 mmol_c L^-1; Mg²⁺ - 2.60 mmol_c L^-1; Na⁺ - 3.4 mmol_c L^-1; K⁺ - 0.2 mmol_c L^-1, and Cl^- - 7.8 mmol_c L^-1.

Based on the results obtained in the water analysis, it can be seen that for the arugula and jambu crops, the SAR and pH values of the water were considered normal. The EC showed an acceptable salinity value in terms of tolerance, as the tolerance of arugula was as high as 2.75 dS m^-1 (Silva et al., 2013) and that of jambu was as high as 3.30 dS m^-1. Both crops are classified as moderately sensitive to salinity (Hoagland & Arnon, 1938).

The experimental design was randomized blocks, with a split-plot arrangement, with 20 treatments (4 × 5) and four replicates. (1) The plots consisted of irrigation treatments: DI50 - deficit irrigation with 50% crop evapotranspiration (ETc); DI75 - deficit irrigation with 75% ETc; TI100 - total irrigation with 100% ETc; EI125 - excess irrigation with 125% ETc; and EI150 - excess irrigation with 150% ETc. (2): The subplots were constituted by the cropping systems, with arugula (primary crop) and jambu (secondary crop). The systems were arugula intercropped, jambu intercropped, arugula in monoculture and jambu in monoculture. The experimental plot had area of 8.4 m² (1.0 × 8.4 m) with usable area of 1.68 m² (42 plants). The subplots were 2.8 m² (1.0 × 2.8 m), with a usable area of 0.56 m² (14 plants). In the single and intercropped crops, the spacing was 0.2 m between plants and 0.2 m between cultivation rows.

Seeds of broadleaf arugula were used. The seeds of jambu, with purple flowers, were obtained from the main producing region of the state of Pará, with geographic coordinates 1° 27’ 31” S and 48° 26’ 04.5” W.

Arugula and jambu seedlings were produced in 200-cell polyethylene trays, with a volume of 18 cm³ per cell. These were filled with substrate containing 90% earthworm humus and 10% vermiculite. After sowing, the trays were placed in a shelter covered with 30% shading, and they remained there until they had 3 to 4 definitive leaves. After this period, the seedlings were transplanted to the field.

A drip irrigation system, with 16-mm-diameter emitters spaced every 0.3 m, a nominal flow rate of 1.6 L h^-1, and a working pressure of 98063.8 Pa, was used to form a wetted strip. Water was applied to the crop daily at 8:00 a.m. and 4:00 p.m.

The water requirement of the crops was determined by obtaining the reference ET (ETo) using evaporation readings measured in the class A pan (CAP), and the pan coefficient (Kp) was determined according to Bernardo et al. (2019).

The ETc value was obtained by the product of the ETo value and the crop coefficient (Kc). The Kc was calculated for the main crop (arugula) as a function of the days after transplanting (DAT), and at 0-8, 9-16, 17-24, 25-33, and 34-40 DAT, and the Kc values were 29, 0.52, 0.93, 0.87, and 1.02, respectively, based on Santana et al. (2016).

The mean ETo in the municipality of Pentecoste, Ceará, is 7.56 mm per day (Macêdo et al., 2018). The daily ETc in the two experimental periods ranged from 0.6 to 6.7 mm per day during crop development, with a maximum peak close to harvest, i.e., at 40 DAT. The irrigation application time was calculated according to the equation of Bernardo et al. (2019) (Eq. 1).

$$Ti=\frac{ETcloc\times Se\times Sf\times FL\times 60}{NEP\times Ea\times qa}$$ (1)

where:

Ti - irrigation time (minutes);

ETcloc - localized crop evapotranspiration (mm per day);

Se - spacing between emitters (m);

Sf - spacing between lateral lines (m);

FL - percentage of the depth defined by treatment (%);

NEP - number of emitters per plant;

Ea - application efficiency (%); and,

qa - mean flow of each emitter (L h^-1).

The accumulated volumes of water applied per treatment during crop development corresponding to replacement rates of 50, 75, 100, 125 and 150% of ETc were 74.25, 108.56, 142.87, 177.18 and 211.18 mm per cycle in 2018 and 77.63, 114.07, 150.52, 186.96 and 223.40 mm per cycle in 2019, respectively.

Soil moisture was determined using the standard oven method every 15 DAT for the crops in both treatments at a depth of 0-30 cm. The wet weight of the sample was determined, and the collected soil was stored in capsules. The samples were placed in a forced-air oven and kept for 24 hours at 105 °C. After this period, the dry weights of the samples were determined according to Bernardo et al. (2019).

The biological efficiency was measured by the index of land use efficiency (LUE), the relative contribution of a main crop to the LUE, and the productivity index of the cropping system. Biological efficiency is characterized by the gain an intercropping system has over a single-cropping system in terms of crop yield and better land use.

The LUE index may reveal advantages of specific land use types; i.e., an intercropping system may experience greater gains compared to a single-cropping system. In this study, calculating partial LUE involved the production per plant in each intercropped treatment for a single plant. The total LUE was determined by summing the partial LUE values of both crops according to the formula proposed by Willey (1979) (Eq. 2, 3 and 4).

$$LUE partial Arugula=\frac{Yaj}{Yaa}$$ (2)

$$LUE partial Arugula=\frac{Yja}{Yjj}$$ (3)

$$LUE Total=\frac{Yaj}{Yaa}+\frac{Yja}{Yjj}$$ (4)

where:

Yaj - yield of arugula intercropped with jambu (kg ha^-1);

Yja - yield of jambu intercropped with arugula (kg ha^-1);

Yaa - yield of arugula in monoculture (kg ha^-1); and

Yjj - yield of jambu in monoculture (kg ha^-1).

LUE > 1 indicates production advantage for the intercropping system and high land use efficiency, and LUE < 1 indicates no production advantage for the intercropping system (Zeng et al., 2019).

The relative contribution of the main crop (RCC) to the LUE index indicated how much the main crop contributed to a better use of the space designated for cultivation and how much the secondary crop complemented the yield of the system. The RCC was calculated according to Souza & Macedo (2007).

The system productivity index (SPI) standardized the yield of the secondary crop in relation to the main crop and was evaluated according to Odo (1991).

Water use efficiency (WUE) was determined by the relationship between the yield values (kg ha^-1) of the single-cropping system and the respective amounts of water applied (m^-3) in each treatment during cultivation.

The WUE of the intercropping system was determined by the relationship between the SPI values and the respective amounts of water applied (m³) in each treatment during cultivation.

Plant height (cm) and root length (cm per plant) were also evaluated, and these measurements were performed with a ruler graduated in cm; the fresh masses of leaves and roots per plant (g per plant) was obtained by weighing on a precision scale with 0.0001 precision; the dry masses of leaves and roots per plant (g per plant) were used to obtain the total dry mass, and the plant materials were placed in paper bags and then in a forced air oven at a temperature of 65 °C where they were kept for 48 hours or until a constant dry mass was obtained. Yield (kg ha^-1) was estimated by determining the fresh mass of arugula leaves and stems and the fresh mass of jambu leaves, stems, and inflorescences per usable area and converting the results to kg ha^-1 (Sampaio et al., 2019).

The assumptions of normality, homogeneity, and additivity were evaluated. The analysis of variance for each of the variables studied in each cycle was performed by the F test. When the significance of the variables was identified, the Scott‒Knott test was applied (p ≤ 0.05) to identify the best cultivation and irrigation system using Sisvar software (Ferreira, 2011).

Results and Discussion

The water content in the soil was similar between the years; however, compared to the single-cropping systems, the intercropping system had a higher water content most likely because it had greater coverage of the soil surface, resulting in a reduction in ET, which promoted a greater water conservation. Higher soil moisture levels in intercropping systems than in monoculture systems have also been reported in other studies (Fan et al., 2016; Silva et al., 2020).

The average soil water content in the two cropping seasons was in the order of intercropping system > single-cropping arugula > single-cropping jambu, and for the irrigation treatments, the order was EI150 > EI125 > TI100 > DI75 > DI50.

According to the obtained results, there was no interaction between the irrigation depths and the cropping systems. Thus, both factors were analysed separately, and different behaviours were observed with respect to the biometric characteristics of the cropping treatments.

In general, the intercropped system played a relevant role in the growth and production of intercropped arugula plants (Table 1).

Table 1
Morphological characteristics of arugula intercropped with jambu and arugula in monoculture for the different irrigation treatments in the experimental periods of 2018 and 2019

Treatment	NL	PH	LFM	LDM	RFM	RDM
2018
DI50	38.725.39 b	26.541.97 a	82.951.76 e	7.870.21 c	8.610.45 a	1.140.08 a
DI75	44.127.20 a	28.821.42 a	161.744.12 a	11.340.29 a	10.731.34 a	1.640.45 a
TI100	30.973.20 b	27.611.20 a	131.265.32 b	11.570.33 a	8.201.94 a	1.120.26 a
EI125	32.017.93 b	24.174.26 b	105.723.22 c	9.460.54 b	7.221.44 a	0.740.11 b
EI150	22.955.90 c	21.771.83 b	95.702.14 d	9.000.35 b	8.460.94 a	0.550.10 b
p value	0.03	0.27	< 0.01	< 0.01	0.13	0.01
F value	3.70*	1.63ns	144.44**	22.44**	2.20ns	4.61**
Arugula	27.364.97 b	24.822.48 a	83.153.15 b	7.87 ± 0.35 b	5.590.76 b	0.770.18 b
Arugula + Jambu	40.156.87 a	26.741.79 a	118.173.05 a	11.83 ± 0.33 a	11.701.67 a	1.310.22 a
p value	≤ 0.01	0.07	≤ 0.01	≤ 0.01	≤ 0.01	≤ 0.01
F value	10.38**	3.64ns	185.65**	340.14**	51.23**	20.52**
2019
DI50	37.023.89 a	23.231.39 b	77.563.64e	7.57 ± 0.66 d	6.740.62 b	1.350.08 a
DI75	37.164.08 a	23.611.32 b	130.915.34 a	14.30 ± 0.15 a	7.860.88 a	1.360.14 a
TI100	40.053.23 a	26.171.15 a	117.483.86 b	14.35 ± 0.45 a	7.900.47 a	1.650.11 a
EI125	36.254.15 a	25.400.76 a	106.712.63 c	12.40 ± 0.56 b	6.140.45 b	1.210.22 a
EI150	36.082.61 a	26.800.72 a	97.221.71 d	9.64 ± 0.34 c	6.130.22 b	1.190.22 a
p value	0.65	0.06	< 0.01	< 0.01	0.017	0.15
F value	0.61ns	3.00ns	44.14**	58.60**	4.57*	2.0ns
Arugula	33.492.90 b	24.211.13 b	80.492.70 b	10.24 ± 0.42 b	5.970.54 b	1.210.12 b
Arugula + Jambu	41.134.28 a	25.870.99 a	131.464.16 a	13.06 ± 0.44 a	7.930.51 a	1.500.19 a
p value	≤ 0.01	0.018	≤ 0.01	≤ 0.01	≤ 0.01	0.02
F value	8.96**	7.01**	599.77**	82.61**	26.73**	6.20*

• NL - Number of leaves per plant; PH - Plant height; LFM - Leaf fresh mass; LDM - Leaf dry mass; RFM - Root fresh mass; RDM - Root dry mass; DI50 - Deficit irrigation, 50% ETc; DI75 - Deficit irrigation, 75% ETc; TI100 - Total irrigation, 100% ETc; EI125 - Excess irrigation, 125% ETc; EI150 - Excess irrigation, 150% ETc. Data represent the means +/- standard errors of the means (n = 4). The mean values followed by the same letter in each factor are not significantly different (p ≤ 0.05) according to the Scott‒Knott test

Arugula had the highest number of leaves and leaf and root fresh and dry masses in both years of study, 2018 and 2019. For the variable plant height in 2018 and root length in 2019, there was no difference when the crop was cultivated in a single-cropping system or an intercropping system.

The best responses observed for the variables leaf and root fresh and dry masses were most likely due to the higher number of leaves observed for intercropped arugula plants. This result occurred because the leaves are photosynthetic organs responsible for intercepting light energy, which is used in the photochemical phase of photosynthesis to produce photoassimilates (Taiz et al., 2017). The higher number of leaves may have enabled greater light interception and, consequently, greater accumulation of biomass in the shoots and roots.

In general, in comparison to the single-cropping systems, the intercropping system provided better development conditions for the plants. In several published studies, it was found that cultivation with intercropping systems maximizes the use of natural resources and area, promoting a decrease in the use of inputs, and promotes ecological balance to improve the growth and development of combined crops within the system (Koefender et al., 2016).

Regardless of the irrigation treatments, in comparison to the single-cropping system, the intercropping system was more effective in terms of the morphological characteristics of arugula. A higher arugula biomass was obtained with the DI75 treatment, with values of 161.74 and 130.91 g per plant in 2018 and 2019, respectively (p < 0.01, Table 1).

On the other hand, for jambu the plants cultivated in a single-cropping system had the highest values of height, shoot fresh mass and shoot dry mass in 2018 and the highest number of leaves, height, shoot fresh and dry mass, root fresh mass, and root length in 2019 (Table 2).

Table 2
Morphological characteristics of jambu intercropped with arugula and in monoculture for different irrigation treatments in the experimental periods of 2018 and 2019

Treatment	NL	PH	SFM	SDM	RFM	RDM	RL
2018
DI50	13.420.42 a	20.940.79 b	29.713.91 d	3.730.39 b	4.600.57 a	0.610.08 b	14.771.72 a
DI75	13.720.87 a	23.421.89 a	41.262.62 c	3.830.34 b	4.891.02 a	0.700.15 b	14.061.41 a
TI100	15.232.01 a	24.161.54 a	55.661.98 b	5.130.19 a	5.160.95 a	1.180.38 a	14.121.20 a
EI125	13.280.94 a	25.521.07 a	62.351.37 a	5.490.22 a	5.201.12 a	1.121.20 a	13.640.62 a
EI150	12.220.70 a	21.350.87 b	44.493.50 c	3.970.30 b	5.060.44 a	0.991.28 a	13.440.44 a
p value	0.188	< 0.01	< 0.01	< 0.01	0.94	< 0.01	0.73
F value	1.82ns	5.61**	56.03**	22.17**	0.183ns	6.64**	0.50ns
Jambu	12.741.16 a	24.191.22 a	49.972.28 a	5.200.31 a	3.91 0.52 b	0.710.16 b	12.850.99 b
Jambu + Arugula	14.410.81 a	21.961.24 b	43.423.06 b	3.650.26 b	6.051.45 a	1.130.20 a	15.161.16 a
p value	0.04	0.03	< 0.01	< 0.01	0.011	< 0.01	< 0.01
F value	4.61*	5.66*	12.64**	47.55**	8.24**	27.17**	11.66**
2019
DI50	11.190.18 b	23.081.39 b	27.230.99 d	3.860.39 b	1.200.07 a	0.500.07 a	13.961.62 a
DI75	11.961.00 b	26.512.71 a	28.710.96 d	3.990.45 b	1.32 0.07 a	0.490.07 a	11.980.97 a
TI100	12.330.60 b	28.12 2.82 a	42.482.65 b	6.520.40 a	1.590.44 a	0.610.16 a	13.891.12 a
EI125	13.800.47 a	28.753.46 a	48.302.53 a	5.640.52 a	1.590.39 a	0.560.08 a	13.720.71 a
EI150	11.780.72 b	22.812.50 b	34.320.92 c	4.760.58 b	1.410.33 a	0.520.03 a	11.941.06 a
p value	0.03	0.03	<0.01	<0.01	0.52	0.64	0.09
F value	3.53*	3.62*	60.02**	8.99**	0.83ns	0.63ns	2.52ns
Jambu	12.760.54 a	44.881.99 a	44.881.51 a	6.23 (± 0.68) a	1.890.33 a	0.580.09a	14.680.81 a
Jambu + Arugula	10.890.65 b	23.243.16 b	23.241.71 b	3.68 (± 0.26) b	1.000.28 b	0.490.08 a	11.521.18 b
p value	< 0.01	0.02	< 0.01	< 0.01	< 0.01	0.29	< 0.01
F value	21.80**	6.22*	159.69**	55.39**	0.27**	1.57ns	15.04**

• NF - Number of leaves per plant; PH - Plant height; SFM - Shoot fresh mass; SDM - Shoot dry mass; RFM - Root fresh mass; RDM - Root dry mass; RL - Root length; DI50 - Deficit irrigation, 50% ETc; DI75 - Deficit irrigation, 75% ETc; TI100 - Total irrigation, 100% ETc; EI125 - Excess irrigation, 125% ETc; EI150 - Excess irrigation, 150% ETc. Data represent the means +/- standard errors of the means (n = 4). The mean values followed by the same letter in each factor are not significantly different (p ≤ 0.05) according to the Scott‒Knott test

Most likely, the intercropped arugula promoted a strong competitive effect on the growth of jambu, which was evidenced by the low yield of the latter in both years of cultivation. The way each crop uses environmental resources can alter the competitive dynamics between the components, potentially having both inter- and intraspecific competition. This may have occurred due to competition for water, light, and nutrients (Zeng et al., 2019).

However, in intercropping systems, there may be positive interactions that compensate for negative interactions, such as facilitation and complementarity (Ren et al., 2016), and in this study, facilitation surpassed interspecific competition. Facilitation occurs when a species in a system improves the development, growth, or survival of the other species through stress mitigation (Ren et al., 2016), which may have occurred in the case of arugula for this study.

Competition for underground resources, including water and nutrients, plays a key role in the results obtained in intercropping systems. The better development of arugula with jambu can be attributed to its faster growth or to other factors, such as physiological efficiency, morphology, and the nutritional need of each crop (Ren et al., 2016).

However, in 2019, for root dry mass, no difference was observed when the species were cultivated individually or intercropped.

The irrigation depths had different effects on the development of jambu (Table 2). All traits evaluated, except for the number of leaves, root fresh mass and root length in 2018 and fresh and dry mass and root length in 2019, were significantly different (p < 0.01 and p < 0.05, respectively).

For jambu, the EI125 irrigation resulted in a greater fresh mass of the leaves. Although jambu showed better performance with EI125, which may be related to the fact that the crop is ecophysiologically adapted to its region of origin (Amazon region), which is a location with high water availability, there was no difference in dry mass when the TI100 treatment was applied, i.e., the amount of water provided by TI100 met the crop water requirements, which suggests that jambu can be grown in the intercropping system with arugula and/or grown in monoculture using the Kc of arugula.

Differences were observed between the irrigation depths and the cropping systems, as well as their interactions for crop yield (Figure 1). For the yield evaluated at 40 DAT, both the intercropped plants and those cultivated in monoculture showed different responses. In general, the highest values were observed for plants grown in monoculture (Figures 1A and 1B).

Figure 1
Yield of arugula in a system intercropped with jambu and in a monoculture with different irrigation treatments in 2018 (A) and 2019 (B)

The yield of arugula was higher in the single-cropping system than in the intercropping system in all water treatments applied (Figure 1). However, when working with the intercropping system, the analysis of yield had its importance reduced when calculating the biological indices of the system because these indices allowed a more uniform and fair evaluation and comparison between the single-cropping and intercropping systems.

Arugula, regardless of the cropping system, showed an increase in yield when DI75 was applied when compared to the other irrigation depths (p < 0.01) in 2018 (Figure 1); however, in the single-cropping system, there was no difference when DI75 and TI100 were applied in 2019, suggesting that intercropping had the advantage of tolerating a 25% reduction in water available for arugula.

On the other hand, jambu showed higher yield with EI125 for the single-cropping system (p < 0.01), and in the intercropping system, no difference was observed between TI100 and EI125 for the two years of evaluation (Figures 2A and 2B).

Figure 2
Yield of jambu in the intercropping system with arugula and in the monoculture with irrigation treatments in 2018 (A) and 2019 (B)

These results suggest that the use of the intercropping system made it possible to use a smaller water depth (DI75), which is important because water has become an increasingly expensive and scarce good (Rodríguez-Calzada et al., 2019).

The lower jambu production in the intercropped system at a spacing of 20 × 20 cm was probably due to competition for light caused by the more developed arugula canopy. This may have resulted in a reduction in the interception of light by jambu and, consequently, caused a decrease in its photosynthetic capacity, resulting in the low yield of the plants in the intercropping system.

A possible solution for improving the production efficiency of jambu would be planting the component crops, arugula and jambu, at different times. Such management could alternate the demands for natural resources of these species over time, which could minimize interspecific competition (Jahansooz et al., 2007).

The results suggest that the intercropping systems of arugula and jambu, subjected to different water levels, had an advantage in yield. In general, a LUE greater than 1 indicates that intercropping has a production advantage and greater land use efficiency compared to a single-cropping system (Zeng et al., 2019). This greater efficiency is attributed to the complementary use of resources from the cultivation area, in which the component crop uses limiting resources more efficiently due to different temporal, spatial, and phenological characteristics (Hendges et al., 2019).

Except for the first year, in which no significant differences were found, in 2019, a difference was observed between the intercropping system for the partial LUE_a and total LUE_{a + j} (Table 3). The intercropping system resulted in the highest partial LUE values for arugula compared to jambu (p < 0.01), which reinforces the hypothesis that arugula was the dominant species in this production system.

Table 3
Biological efficiency of the intercropping (LUE) of arugula and jambu in different irrigation treatments in the experimental periods of 2018 and 2019

Treatment	LUEa	LUEj	LUE a + j	RCC (%)	SPI
2018
DI50	0.710.02a	0.510.11a	1.220.10a	61.465.17a	13792.94423.12e
DI75	0.850.03a	0.410.03a	1.260.013a	62.842.17a	27183.32635.73a
TI100	0.870.06a	0.450.018a	1.360.06a	56.271.87a	24737.28603.98b
EI125	0.740.04a	0.450.012a	1.150.05a	65.290.66a	21392.91462.65c
EI150	0.750.02a	0.490.05a	1.160.08a	65.262.38a	17464.40506.49d
p value	0.08	0.56	0.31	0.42	≤0.01
F value	0.22	0.76	1.31	1.04	84.82
2019
DI50	0.620.04c	0.460.02a	1.080.04c	57.312.46c	12628.90618.61d
DI75	0.960.05a	0.480.02a	1.440.03a	66.812.20a	23103.43652.75a
TI100	0.840.03b	0.45 0.04a	1.280.06b	65.431.79a	21570.78570.49b
EI125	0.830.03b	0.450.04a	1.280.06b	65.081.86a	21124.65589.25b
EI150	0.780.01b	0.490.01a	1.270.003b	61.451.22b	17388.46209.32c
p value	≤ 0.01	0.72	≤ 0.01	≤ 0.01	≤ 0.01
F value	11.71	0.52	6.18	11.16	61.84

• LUEa - Partial land use efficiency of arugula; LUEj - Partial land use efficiency of jambu; LUEa + j - Total land use efficiency of the system; RCC - Relative contribution of the main crop; SPI - System productivity index of arugula intercropped with jambu and in monoculture with irrigation treatments in 2018 and 2019. Data represent the means +/- standard errors of the means (n = 4). The mean values followed by the same letter in each factor are not significantly different (p ≤ 0.01) according to the Scott‒Knott test

For 2019, the maximum LUE_a occurred when DI75 was used, with values of 0.96 and 1.44 for partial LUE_a and total LUE_{a + j}, respectively. This indicates that this treatment resulted in greater biological efficiency. On the other hand, the LUE decreased when the DI50 treatment was applied or when there was an increase in water availability via irrigation. Thus, the increase in water availability did not contribute to increasing the partial LUE of arugula and the total LUE of the system.

Based on the observed results, the calculated LUEs were 1.08, 1.44, 1.28, 1.28 and 1.27 for the DI50, DI75, TI100, EI125 and EI150 treatments, respectively, in 2019; thus, 8, 44, 28, 28 and 27% more area is needed for the crops in a monoculture system to produce the equivalent of that in the intercropping system in terms of water availability (Willey, 1979).

The lower yield, as well as the reduction in the LUE for the DI50 treatment, was possibly related to the negative effect caused by water deficit stress. Similarly, the lower yield and LUE observed for irrigation greater than DI75 may have occurred due to excess water, which is also harmful to crops, as it can cause physiological disorders, such as anoxic stress (lack of O₂ in the root), root rot (Taiz et al., 2017), and greater infestation by diseases (Agrios, 2005).

Thus, the relative contribution of arugula to the LUE in the intercropping system in 2019 was higher for DI75 (66.81%) than for the other irrigation treatments; however, there was no difference between TI100 and EI125, which had RCC values of 65.43 and 65.08%, respectively. For the DI50 and EI150 treatments, the contributions to LUE were 57.31 and 61.45%, respectively. This shows that the irrigation treatments affected the biological efficiency of the system (Table 3).

The potential of the intercropping system was directly influenced by the complementary use of environmental resources by the species; in addition, the relative strength of intra- and interspecific competitive interactions between the crops in the system influenced this factor (Ren et al., 2016).

The system’s productivity index confirms that the intercropping promotes biological efficiency and that DI75 was superior to the other treatments for both 2018 and 2019, with 4,799.99 and 2,978.82 kg ha^-1 higher yield for the main crop, respectively, compared to the yield of their single crops (Table 3).

Differences were observed (p < 0.01) between irrigation and the cropping system, as well as their interactions for WUE in 2018 and 2019 (Figures 3A and B).

Figure 3
Water use efficiency of arugula in the intercropping system with jambu and in the monoculture with irrigation treatments in 2018 (A) and 2019 (B)

For the main crop, there was no difference in the WUE regarding the cropping system evaluated in the two experiments performed in different years, except when treatments DI50 and DI75 were applied in 2018 and DI50 in 2019. The irrigation that resulted in a greater WUE in the intercropping system was DI75 (25.03 kg m^-³) in 2018 and (20.25 kg m^-³) in 2019, and the values were reduced when plants were exposed to DI50, TI100, EI125, and EI150.

For the secondary crop, the DI75 treatment resulted in a higher WUE; however, there was no difference when applying DI50, TI100 and EI125 (p < 0.01) in 2018. In 2019, the DI50 treatment resulted in a higher WUE, while the DI75 treatment resulted in a lower WUE. TI100 and EI125 showed similar behaviours (p < 0.01) (Figures 4A and 4B).

Figure 4
Water use efficiency of jambu in monocultures with irrigation treatments in 2018 (A) and 2019 (B)

In intercropping systems with at least two crops with different architectures and growth dynamics, the crops involved in the system can create strategies that transmit positive water use effects in the soil, which may have favourable effects on biomass production (Morris & Garrity, 1993). However, the data obtained in this study show that there was possible competition between plants, for both resources and space. This result may have occurred mainly due to the similarity in the phenology of the species. In addition, another aspect that may have influenced the results was the arrangement used in the intercropping system; however, the results demonstrate the potential of an intercropping system as functionally diversified to increase WUE, i.e., use the same amount of water to increase crop production. This result can be confirmed by the increased growth of the main crop in the intercropping system in the DI75 treatment.

Conclusions

1. The combination of arugula and jambu, considering the land use efficiency index, especially under deficit irrigation with 75% ETc (DI75) stands out when the objective is to maximize the total yield per area of ​​the crops, instead of focusing on the isolated performance of each one.

2. The best irrigation was DI75 for arugula and total irrigation with 100% ETc (TI100) and excess irrigation with 125% ETc (EI125) for jambu.

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• ¹ Research developed at Universidade Federal do Ceará, Centro de Ciências Agrárias, Fortaleza, CE, Brazil

Supplementary documents

• There is no supplementary research data.

Financing statement

• There was no research funding.

Edited by

• Editors: Ítalo Herbet Lucena Cavalcante & Walter Esfrain Pereira

Data availability

There is no supplementary research data.

Publication Dates

• Publication in this collection
  03 Feb 2025
• Date of issue
  June 2025

History

• Received
  06 Jan 2024
• Accepted
  14 Nov 2024
• Published
  16 Dec 2024