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Article

Simultaneous Assessment of Water and Nitrogen Use Efficiency in Rain-Fed Chickpea-Durum Wheat Intercropping Systems

by
Omar Kherif
1,
Benalia Haddad
1,
Fatma-Zohra Bouras
1,
Mounir Seghouani
1,
Bahia Zemmouri
1,
Ramzi Gamouh
1,
Nadia Hamzaoui
1,
Amira Larbi
1,
Nazih-Yacer Rebouh
2 and
Mourad Latati
1,2,*
1
Laboratoire d’Amélioration Intégrative des Productions Végétales (C2711100), Département de Productions Végétales, Avenue Hassane Badi, Ecole Nationale Supérieure Agronomique (ES1603), El Harrach, Algiers 16200, Algeria
2
Department of Environmental Management, Peoples’ Friendship University of Russia (RUDN University), 117198 Moscow, Russia
*
Author to whom correspondence should be addressed.
Agriculture 2023, 13(5), 947; https://doi.org/10.3390/agriculture13050947
Submission received: 14 January 2023 / Revised: 22 February 2023 / Accepted: 24 April 2023 / Published: 25 April 2023
(This article belongs to the Special Issue Conservation Agriculture, an Alternative for Sustainable Farming)
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Abstract

:
It is well known that multiple interactions can occur between nitrogen and water use, depending on climate, soil and crop characteristics, in crop growth and yield development. However, little is known about the simultaneous change in both water and N use efficiency (WUE and NUE) and their possible interactions in cereal–-legume intercropping systems. In order to advance our knowledge on the N and water facilitation mechanisms involved in the intercropping responses of N and water input co-limitations, we investigated, via four experiment years, the simultaneous optimization of water and N-fertilizer inputs, as well as its possible effects on growth, yield, N acquisition, and the NUE and WUE in intercropped species. The results indicated that intercropping increases the leaf area index by more than +0.14 and +1.03 units when compared to durum wheat and chickpea monoculture systems, respectively. This increase is particularly noticeable under higher rainfalls during the crop period (i.e., as can be seen in the 2022, 2020, and 2019 seasons). Moderate N-application enhanced both the grain yield and protein accumulation in the mixed crops by more than 0.22 t ha−1 and 57 kg ha−1, respectively. Conversely, intercropping significantly decreased the mixed grain yield when compared to durum wheat monocultures. Intercropping advantages in terms of biomass (ranged from 1 to 44%) and N-acquisition (2 to 91%) was confirmed in either low- (2021) or high- (2019 and 2022) rainfall growing periods, but only under low and moderate N-applications. Improving N nutrition under both rainfall and drought growth periods was confirmed only for the mixed crops under all applied N-fertilizer doses. Such improvements in growth, N acquisition, and yield quality were most likely achieved by positive interactions (r2 = 0.73, p ≤ 0.001) between the NUE and WUE for the chickpea–wheat intercropping. Thus, 0.62 kg m−3 of WUE promotes a significant increase of 1 kg kg−1 in NUE by mixing chickpea-durum wheat. Rain-fed chickpea-durum wheat intercropping provides a higher performance in growth and yield quality compared to sole cropping systems; this may occur from the simultaneous optimizations of both water and N fertilizer inputs in low-N soil under semiarid conditions.

1. Introduction

The continuous growth of the world population results in a higher demand for food products. Consequently food production must double by 2050 in order to cover this alimentation need [1]. This increase in food production needs to be achieved in the face of an increasing scarcity of water and nutrient resources [2]. Water and nitrogen (N) are considered the most limiting factors for crop growth and yield [3,4]. One of the main strategies in overcoming water and N deficits is the improvement of both water and N use efficiency (WUE and NUE). This is especially true under low-input conditions [5,6,7]. Water availability greatly affects the N status of both soil and plants. It is also considered a key indicator in evaluating the N response of rain-fed cropping systems [8]. Hence, water limitation also affects the way in which N inputs (i.e., organic and mineral fertilizers) are absorbed by crops; additionally, it also deeply affects growth and crop yield [9].
Many research studies have focused on the main factors that improve either WUE or NUE, including the role of crop genetics, environmental conditions, and agricultural management practices [10,11,12]. The last few studies described WUE and NUE separately at various scales from field to landscape. However, the interaction between WUE and NUE has been poorly documented in the literature. Innovative agricultural practices aim to simultaneously improve both the WUE and NUE in order to optimize the use of water and N inputs, especially under low-input agricultural practices [13,14,15]. Plett et al. (2020) highlight the need to identify and assess the interaction effect between water and N, as well as how their co-limitation affects crop biomass and yield [8].
At the cropping management level, many traditional (i.e., crop rotation and cover crop) and modern (i.e., monoculture intensification, crop breeding, and weeding control) practices are developed to enhance crop yield, biomass, and yield quality [16,17]. However, these practices may affect the regulation and use of water and N at leaf (i.e., photosynthesis and evapotranspiration), biomass, and grain-yield levels [18]. For example, excessive N and water inputs, either applied by farmers (i.e., fertilization and irrigation) or by those which are naturally available for crops (i.e., rain and available-N from organic matter mineralization) globally contributed to enhancing water and N losses by evapo-transpiration and N leaching (and/or denitrification), respectively [19]. Agroecological intensification is currently considered an innovative practice that enhances both WUE and NUE. In recent years, cereal crop diversification through the cultivation of legume species in intercropping with cereals has been strongly adopted to improve water use and crop productivity. This may occur due to the direct reducing of soil-water evaporation, which leads to an efficient sharing of water for plant transpiration [20,21]. Recent research studies have demonstrated that the increase in WUE by intercropped maize with either durum wheat or forage pea is strongly related to the increase in the yield per units of water supplies [22].
Regardless of the recent literature, a review of intercropping on water and nitrogen use efficiency is lacking, while the direct and indirect mechanisms that are involved in increasing WUE remain poorly documented [23,24]. The increase in NUE was confirmed for legume and cereals in intercropping systems, which were demonstrated as sustainable practices (i.e., in terms of agroecosystem performance and resilience). Furthermore, they could reduce N-fertilizers application [25]. Therefore, the N status at soil and crop levels is directly related to water availability from either irrigation or rainfall inputs. Consequently, water limitation leads to a significant decrease in NUE when N inputs are not optimally available when compared to crop demand [26].
In the semiarid regions of Algeria, durum wheat-fallow rotation is the most common practice. It is widely adopted by farmers for cereal food production. This cropping practice is considered an extensive system, which satisfies only slightly less than the half of the wheat food demand of the Algerian population [27]. However, in sub-humid areas, durum wheat is mainly cultivated in rotation with either legumes or other vegetable crops, where the optimal water availability of rain leads to the yield stability of rotated legumes [28].
Currently, Algerian farmers aim to develop cereal–legume intercropping as an alternative solution for increasing land use, profitability, and farm sustainability. Grain legume–durum wheat intercropping has been reported as an efficient cropping practice by which to reduce the global requirements for water and N inputs, through irrigation and N-application, respectively [29,30]. This intercropping advantage was also confirmed by a recent field research that was performed at farmer plots in the semiarid plains of Algeria—a country that suffers from a serious water deficit and limited access to N-fertilizers [31]. As an example, the data from field experiments on durum wheat that are intercropped with faba beans and chickpeas showed that intercropping was more efficient in terms of increasing either the WUE or NUE when compared to their respective monoculture and rotation systems [31,32]. In view of this interest, the response of cereal–legume intercropping to water and N availability was actively investigated in recent research works. However, the effect of N and water on these cropping systems was mainly studied separately. Consequently, we have little evidence on the possible co-limitation (i.e., N and water resources) effect on biomass and yield productivity [26,33]. Meanwhile, the assessment of the possible interactions between WUE and NUE may provide a novel approach, and may help in finding how to apply this intercropping system as an innovative practice. Ultimately, this may result in a simultaneous optimization of water and N use, particularly in the context of low-input agriculture.
The present research study focuses on the agroecological intensification of chickpea and durum wheat crops, which are considered the two main strategic crops for food production in Algeria. The main objective of the present study is to evaluate the interaction between N and water-use efficiency in the practice of durum wheat–chickpea intercropping when under the contrasted supply of N-fertilizers. We hypothesize that both moderate N-application and water availability will simultaneously enhance the WUE and NUE in intercropping systems (while these indicators are also optimized separately in monocultures). This field research addresses three basic questions: (i) Does the cropping season × N supply interaction affect the growth and yield response of either chickpea or durum wheat in intercropping systems?; (ii) can chickpea intercrops improve N nutrition for durum wheat through the optimization of water use under rain-fed conditions?; and (iii) under which conditions of resources availability (i.e., N and water) are both WUE and NUE strongly correlated in rain-fed cropping systems?

2. Materials and Methods

2.1. Site Description and Pedoclimatic Conditions

This field experiment was carried out during four (2018/2019, 2019/2020, 2020/2021, and 2021/2022) cropping seasons from December 2018 to June 2022, under farmer plot conditions. The experiment site was located in the center of Setif region (36°06′13″ N, 5°20′24″ E) in the northeast of Algeria. The soil physical and chemical proprieties, as well as the climate characteristics during the crop period of each season are represented in Table 1.
The soil description that is briefly reported in Table 1 shows that the experiment site had a clay-loam texture with a high proportion of calcareous content (>20%). The soil of the area was considered alkaline (pH > 8) with a low rate of organic matter (1.25%). The total N and phosphorus (P) content were, respectively, 1.33 g kg−1 and 264 mg kg−1, while the site has a relatively low-soil content in terms of available N (22 mg kg−1) and P (9 mg kg−1). Table 1 also shows the historical and the recent meteorological data in the experiment site. The mean of the monthly cumulated rainfall, as well as the mean monthly temperature was, respectively, 315 mm and 14.93 °C during the cropping season.
The accumulated rainfall during the cropping period of each experiment season (from 2018 to 2022) approximately decreased by 17.5% when compared with that which cumulated from 1981 to 2020. However, the mean of the monthly temperature did not deviate substantially between the old (1981–2020) and recent (2018–2022) periods (Table 1). According to the data reported in Table 1, the cumulated rainfall was slightly varied from the first (2018/2019) to the last (2021/2022) growing season, with a difference of 17.03 mm between the higher and lower rainfall seasons. Nevertheless, the mean of the monthly temperatures varied slightly between the old and recent periods. In terms of the monthly rainfall distribution during the cropping period (Figure 1), the data showed a large variability of rainfall among the different growing seasons.
It can be observed from Figure 1 that during the months (i.e., January, February, March, and April) corresponding to the main growth stages (tillering, booting, and inflorescence emergence) of durum wheat, the accumulated rainfall was much lower during 2020/2021 growing season (81 mm) when compared to the other seasons (164, 131.6, and 161.9 mm during 2021/2022, 2019/2020, and 2018/2019 growing seasons, respectively). In the case of the mean monthly temperature, the data show a similar global distribution of temperature between the four growing seasons in the different months of the cropping cycles. From November 2018 to June 2022 the mean monthly temperature ranged from 3.6 to 26.8 °C in January and June, respectively (Figure 1).

2.2. Cropping and Field Plot Design

The study was carried out with two commonly cultivated varieties of both durum wheat (Triticum turgidum durum L.cv. VITRON) and chickpea cultivars (Cicer arietinum L.cv. FLIP 90/13 C). The experimental design involved two combined factors: (i) N-fertilizer rate (dose) represented by the three N-levels, equivalent to 30 (low), 60 (medium), and 100 (high) units per ha−1; and (ii) the cropping system (Crop-syst) treatment that represented the sole-cropped durum wheat, sole-cropped chickpea, and intercropped durum wheat-chickpea. The whole experiment plot contained nine treatments, which were replicated four times for each treatment. All treatments (crop-syst × N-level) were arranged under a randomized complete block (RCB) design.
The sowing density was chosen according to the local farmer practices that corresponded to 350 plants per m² for sole crop durum wheat and 30 plants per m² for monocropped chickpea. Meanwhile, the intercropping plots combined 150 and 18 plants per m² of durum wheat and chickpea, respectively. Intercropping was practiced row by row, alternating between the two cultivated species (ratio 1:1) in the intercropped plots. The distance between the rows was 17 cm for durum wheat in monocultures, while it was 30 cm in the case of chickpea monocultures and intercropping durum wheat-chickpea. Urea (46-0-0) was selected as the N-fertilizer, and was applied during the two periods of cropping time. The first application was performed at the beginning of the tillering stage (durum wheat), where it was applied at 30 units/ha−1 for each N-level treatment. However, the second dose was applied during the stage of stem elongation with the following doses: 0, 30, and 70 units/ha−1 (corresponding to N-30, N-60, and N-100 levels). All cropping systems were sown between 25th November and 15th December during all cropping seasons. The four field experiments were carried out under rain-fed conditions and without either irrigation or weeding management.

2.3. Plant, Soil Sampling and Measurement

At each cropping season, the soil and plants were sampled during three key sampling periods corresponding to the sowing, flowering (130 to 150 days after sowing DAS), and harvest stage (170 to 190 DAS). The soil of the experimental site was characterized by a standard sampling of the top layer (from 0–30 cm soil depth) during the first year of the experiment. Physical and chemical soil analyses were performed during the first growing season with common methods. The total N content in the plant tissues and soil was measured with the Kjeldahl method [34], while the mineral fraction for the degree of N in the soil (N-NO3- + N-NH4+) was determined according to Henriksen’s method. The soil pH was directly determined with a pH meter in a soil-suspension deionized water solution with the ratio = 1:2.5 [35]. The total P content was determined with the Malachite green method after co-digestion by nitric and perchloric acids [36]. Meanwhile, the soil P-available value was measured classically with the Olsen method. For the OM and CaCO3 content in soil, we used, respectively, the Anne and Horton and Newson methods [37,38]. The oven-drying method was performed to measure the soil moisture (at 0–20 and 20–40 cm). The soil was sampled and transferred into a container, weighed under the sampled condition, oven dried, and weighed again after drying (at 105–110 °C). All soil measurements were established with 4 replicates (laboratory), where each replicate corresponded to one composite sample taken from each treatment (four sub-plots). Finally, the volumetric water content (m3 m−3) was estimated by multiplying the bulk soil density by the measured gravimetric moisture.
Plant sampling for the different aboveground variables were performed during both flowering (i.e., leaf area, shoot biomass, and N uptake by plant) and harvest (i.e., yield and grain protein yield) stages. At the flowering stage (130–150 DAS), the durum wheat and chickpea were harvested in each treatment (0.25 m2 quadrat). Shoots were separated from the root at the cotyledonary node and were oven dried during 48 h at 65 °C, then weighed. The leaf area measurements were performed with a leaf area meter (CI-202 portable laser). The ratio of the crop leaf area to land area was calculated to estimate the leaf area index (LAI) [39]. At the harvest stage (170-190 DAS), the grain yield and its components were sampled and estimated by harvesting all aboveground biomass (i.e., chickpea and durum wheat) from the quadrat of 1 m2 in each treatment (four replicates for each treatment). The protein content was calculated (in percent) with the conversion constant k (k = 6.25 and 5.7 for the chickpea and durum wheat, respectively) by converting the N content (in percent) in the grain yield [40].

2.4. Calculation

2.4.1. Land Equivalent Ratio (LER) and Nitrogen Nutrition Index (NNI)

In this field investigation, the performance of crop (i.e., durum wheat and chickpea) N nutrition under the different N-application rates was assessed by using the nitrogen nutrition index (NNI). NNI diagnosis was performed to accurately analyze the in-season crop N status and its changes between both the flowering and harvest stages. The NNI was calculated (Equation (1)) as the ratio of crop N concentration (Na) and the critical N uptake (Nc). Na corresponds to actual crop N concentrations relative to actual crop biomass Wa, while Nc was defined as the minimum level of N uptake that ensures the maximum aboveground biomass accumulation (Equation (2)).
NNI = Na/Nc
Nc = ac W b−1
where ac represents the critical crop N concentration for W (aboveground biomass) = 1 t ha−1. Both ac and b coefficients were determined (5.1 and 0.32 for chickpea and 3.4 and 0.37 for durum wheat, respectively) from the literature [28,41].
To assess the performance of chickpea–durum wheat intercrops in terms of growth, yield, and N acquisition, we calculated the land equivalent ratio (LER), which is considered the main competitive index for evaluating intercropping advantage. The LER was calculated in a similar unit area between both the monoculture and intercropping systems under different N-fertilizer levels (Equation (3)):
LERab = Yab/Yaa + Yba/Ybb
where Yaa and Ybb are the interest variables (i.e., biomass, yield, and N uptake by biomass and yield), and were measured for the sole crop of species a and b, while Yab and Yba are the yields for the intercropping species a and b, respectively [42].

2.4.2. Water Use (WU), Water Use Efficiency (WUE), and Nitrogen Use Efficiency (NUE)

The seasonal evapotranspiration (ET) of each cropping system was calculated with the water balance equation (Equation (4)), which is based on the calculation of volumetric water content at sowing (initial soil moisture) and during the different cropping (i.e., sowing, flowering and harvest) stages [43].
ET= P + I + U – R – Dw – ΔS
Here, P is the rainfall amount (mm) cumulated from the sowing to harvest period, and R is the water amount relative runoff, which was negligible in our field conditions. I represents the amount of irrigation applied during the cropping cycle (I = 0, no applied irrigation over all cropping seasons). U and Dw are defined, respectively, as the upward and downward capillary flow into the rooting area, and the values of U and Dw were considered negligible in the case of our field experiment conditions. ΔS is the change in soil volumetric moisture (converted in mm) at soil layers from 0 to 40 cm (soil depth of experiment site); it was calculated from the difference between the soil moisture measured in both the initial soil and harvested soil at the crop maturity stage.
Additionally, the WUE of each crop was assessed relative to the grain yield (WUEGY) of wheat and chickpea monocultures, as well as for the mixed crop. With respect to this, the WUE of the grain yield in each cropping system (WUEGY) was calculated (Equation (5)) as the ratio between the ET (WU) and grain yield [22]. In the intercropping case, the WUE was calculated by using the mixed grain yield of both of the two intercropped species.
WUEGY = Grain yield/ET
The NUE was also assessed in each crop-syst × N-level treatment and compared across the four years of the field experiment. Calculation was principally performed according to a fertilizer-based approach, in which the NUE was defined as the rate of N fertilizer that was utilized and allocated, corresponding to the N grain yield N [44]. Hence, the NUE was determined by calculating the ratio between the N grain yield and the corresponding rate of applied N-fertilizer (Equation (6)). However, the NUE calculation for the intercropping system was conducted by using the mixed N grain yield of both intercropped species.
NUE = N-uptake GY/N fertilizer dose

2.5. Statistical Analysis

All collected data that are involved in the analysis of variance (ANOVA) were tested in terms of variance homogeneity. A two way ANOVA was performed to assess the effect of the crop-syst, N-level, and crop-syst × N-level interactions on the following measured variables: grain yield (GY), LAI, protein yield, water use (WU), as well as the NUE and WUE. The same statistical analysis was also performed to test the effect of both growing season and N-level treatments on calculated indices (LER and NNI). The levels of significance for each factor effect were performed at the probability of a (p)-value = 0.05. The mean values of each treatment were compared by using Tukey’s test, where the measured variables were significantly affected by the studied factors. However, the relationship between the WUE and NUE was established with a linear regression analysis. All statistical tests were conducted with Statistica 8 for Windows.

3. Results

3.1. Leaf Area Index (LAI) and Grain Yield (GY) Changes

To better assess the growth and crop production, the LAI and grain yield were measured for the durum wheat and chickpea in each crop-syst × N-level treatment. Table 2 shows the LAI and GY values that were measured in each growing season. Results show that the LAI values were significantly affected (p ≤ 0.05) by crop-syst, N-level, and crop-syst × N-level interactions during the four-year period. As a consequence, the LAI of mixed crop was greater than that which was observed in both the durum wheat (+0.14 and +0.29 units among the three N-application rates in the 2022 and 2019 growing seasons, respectively) and chickpea (+1.84 and +1.03 units) monocultures. However, there was a decrease in the intercropping variants when compared to the durum wheat monoculture during both the 2020 and 2021 growing seasons. Furthermore, this was more pounced under N-60 (1.73 and 3.07 units, in the 2021 and 2020 growing seasons, respectively) and N-100 (−1.79 and −3.53 units) applications (Table 2).
In terms of GY, both N-level and crop-syst significantly affected (p ≤ 0.001) the GY of the durum wheat, except in 2021 and 2019 which is where we observed no significant N-application effect. A greater GY was noted in the durum wheat monoculture, which was significantly increased by increasing N-application, particularly in the 2022 and 2020 growing seasons. The results in Table 2 show also that N-application gradually increased the GY of the mixed crop between the N-30 and N-60 doses. Thus, raising the dose from N-30 to N-60 resulted in an increase in the GY of the mixed durum wheat-chickpea by +0.81, +0.24, +0.22, and +0.74 t ha−1 in the 2022, 2021, 2020, and 2019 growing seasons, respectively. However, when considering the difference in grain yield between the N-30 and N-100 doses, there was only a significant increase in the 2020 (+1.71 t ha−1) cropping season.
The same trend was observed, except during the 2021 growing season, for the chickpea monoculture where the GY was significantly increased when passing from the N-30 to N-60 dose. In the case of the durum wheat monoculture, N-application gradually increased the GY among the three N-application doses during all experiment years; this increase was more pronounced (+1.97 t ha−1 passing from N-30 to N-100 dose) in the 2020 growing season when the crop-syst × N-level interaction significantly affected the GY (Table 2).

3.2. Protein Accumulation and Nitrogen Use Efficiency (NUE)

The values of protein yield and the NUE for the chickpea and durum wheat grown under all crop-syst × N-level combinations are given in Table 3. Protein yield was significantly (p ≤ 0.001) affected by the cropping system during all cropping seasons, while they were only affected (p ≤ 0.05) by N-level treatment during the 2022 and 2020 periods, and by crop-syst × N-level interactions in both the 2021 and 2020 growing seasons. The durum wheat monoculture had the highest protein yield when compared to both chickpea monoculture and intercropping systems.
Increasing N-application leads to a gradual enhancing in protein production when increasing the N dose from N-30 to N-100. This increase in protein yield was only significant in the GY of the mixed crop, and only during the 2022 and 2020 growing seasons. Hence, the protein yield was increased by 57 and 133 kg ha−1 when passing from N-30 to N-100 in the 2022 and 2020 growing seasons, respectively. The same trend was observed, specifically in the 2020 growing season (Table 3), for the protein yield of durum wheat. However, the highest protein accumulation was noted under a moderate N-application for the sole-cropped chickpea in both the 2022 and 2022 growing seasons.
Results in Table 3 indicate the NUE values. The interaction between crop-syst × N-level significantly affected (p ≤ 0.001) the NUE during most of the years of the experiment, except during the 2019 growing season. Increasing the N-application from the N-30 to N-100 dose gradually decreased the NUE by 0.02, 1.13, and 0.48 kg kg−1 in the chickpea monoculture and by 0.24, 0.15, and 1.09 kg kg−1 in the durum wheat monoculture in the 2022, 2021, and 2020 seasons, respectively (Table 3). By contrast, the NUE was significantly increased by N-application when increasing the N dose from N-30 to N-100 in the intercropping system. This was only observed in the 2022 and 2020 growing seasons, while the opposite trend was found in the 2021 cropping season. Thus, the NUE for the mixed chickpea-durum wheat was significantly increased by 0.29 (2022) and 0.15 (2020) kg kg−1, but decreased by 0.21 kg kg−1 under the 2021 conditions. In 2019, no significant changes were observed in the NUE for the three studied cropping systems.

3.3. Water Use (WU) and Water Use Efficiency (WUE)

Table 4 shows the measurement of the WU and WUE by grain yield (WUEGY). All crop-syst × N-level combinations significantly affected the WU over most of the years of the experiment, except in the 2021 growing season where WU was only affected by N-level treatment. In general, the highest WU was observed in the 2021 growing season, in which water consumption by the three cropping system was increased by more than an average of 1000 m3 ha−1 when compared to the 2022, 2020, and 2019 growing seasons. For the chickpea monoculture, the WU was globally greater under either low or moderate N-application in 2022 (174 m3 ha−1) and 2019 (33 m3 ha−1), compared to their respective measurements in high N-application (N-100) scenarios. Conversely, the highest values of WU were observed in high N-application contexts during the 2021 and 2020 cropping seasons, with an increase of 150 and 62 m3 ha−1 in water consumption when compared to low N-application (Table 4). For both the sole-cropped durum wheat and mixed crop systems, the WU was generally increased under a low N-application when compared to high N-applications, particularly during the 2022, 2020, and 2019 cropping seasons. Thus, the greatest increase was observed during the 2022 growing season, in which the WU was significantly increased by 325 and 231 m3 ha−1 in the durum wheat monoculture and intercropping system, respectively. In the 2021 growing season, the WU was gradually increased by N-application in the intercropping system, where it was increased by 20 and 110 m3 ha−1 when upgrading from the N-30 to N-60 dose and from the N-60 to N-100 dose, respectively.
In the case of WUE by grain yield, the data show that crop-syst had a significant effect on WUEGY over all cropping years. However, it was only significantly affected (p ≤ 0.05) by both N-level and crop-syst × N-level interactions during the 2022 and 2020 growing seasons. When compared to the chickpea monoculture and intercropping system, the sole-cropped durum wheat was the most efficient crop in terms of water use between the three applied N-fertilizer doses, while the highest WUEGY was noted under both moderate and high N-application. Surprisingly, the greatest WUEGY was observed for the sole-cropped chickpea when compared to other cropping systems, particularly in the 2021 cropping season (Table 4). When considering the mixed crop, the WUEGY was gradually increased when the N dose was increased from N-30 to N-60 (by 0.16 and 0.02 kg m−3 in the 2022 and 2020 growing seasons, respectively) and from N-60 to N-100 (by 0.21 and 0.42 kg m−3 in the 2022 and 2020 growing seasons, respectively).

3.4. Land Equivalent Ratio (LER) and Nitrogen Nutrition Index (NNI)

Table 5 shows all calculated values of the LER in terms of biomass (TB), grain yield, (GY) and N uptake by either biomass (NB) or yield (NY). The ANOVA analysis showed a significant effect (p ≤ 0.05) for all the studied factors on LER values, except for the N-level effect on LERGY. According to the data reported in Table 5, the highest values of LER were observed in the 2019 (1.22) and 2020 (0.80) growing seasons under, respectively, moderate and high N-applications, but they were greater than 1 under only moderate N-application during the 2019 growing season. In terms of N accumulation by grain yield (LERNY), the intercropping advantage was only observed in the 2019 growing season and under moderate N-application, which allowed a more than 65% advantage when compared to sole crop (Table 5). For biomass production, intercropping showed an advantage over the 2019, 2021, and 2022 cropping seasons. This advantage was only observed under both low and moderate N-application in the 2019 (20 and 44% in N-30 and N-60 doses, respectively) and 2022 (5% in N-30 dose) seasons. However, this was confirmed for all applied N doses (19, 1, and 12% in N-30, N-60, and N-100 doses, respectively) in the 2021 growing season. The same trend was found for LERNB, in which low and moderate N-application leads to a greater advantage for intercropping, particularly in the 2019 (91% in N-30 dose) and 2021 (71% in N-60 dose) seasons.
Moreover, Figure 2 shows the calculated values of the NNI for both the chickpea and durum wheat grown as sole crop and intercrop. The NNI was calculated for both flowering and harvest stages in all field experiment years. All the NNI values were below 1 in all plots where the chickpea was grown as sole crop, indicating low N soil availability at the experimental site. The results also show that the highest NNI values were noted in the 2021 growing season at the harvest stage of the chickpea, which varied from 0.73 to 0.90. For the sole-cropped durum wheat, the NNI was greater than 1 in both the flowering and harvest stages in the 2022 and 2021 cropping seasons. This was observed under all N-applied doses, where there were no significant differences in the NNI values between the three doses (Figure 2). Regardless of intercropping, the NNI for mixed chickpea-durum wheat was greater than 1 at the flowering stage in the 2022 and 2021 growing seasons only. We also noticed that it was higher (20%) in the 2021 season when compared to the 2022 growing season for the three N-application doses. At the harvest stage, the NNI was greater than 1 only during the 2019 growing season, indicating an increase of N nutrition for the mixed crop by 11, 30, and 46% (respectively in the N-30, N-60, and N-100 doses) when compared to the critical level of N-nutrition.

3.5. Relationship between WUE and NUE

Since interaction is possible between the WUE and NUE, the values of NUEGY were plotted as a function of the WUEGY in each cropping system. The relationship in Figure 3 indicates that only the durum wheat monoculture and intercropping system had a significant correlation between the WUEGY and NUEGY, regardless of the three studied cropping systems. Contrastingly, the WUEGY of the mixed chickpea-durum wheat was not correlated (r2 = 0.11, p ≤ 0.05) with the NUEGY of the sole cropped chickpea (Figure 3). Nevertheless, the strong relationship between the WUE and NUE was observed in the intercropping system (r2 = 0.73, p ≤ 0.001) and was greater than that which was found in the durum wheat monoculture system (r2 = 0.33, p ≤ 0.05). In the durum wheat monoculture system, each increase of 0.45 kg m−3 in the WUEGY lead to an increase in the NUEGY by 1 kg kg−1. In the case of the intercropping system, 0.62 kg m−3 of WUEGY promoted an increase of 1 kg kg−1 in the NUEGY for the mixed chickpea-durum wheat.

4. Discussion

Our results confirmed that the LAI and aboveground biomass were significantly higher for mixed chickpea-durum wheat when compared with both chickpea and wheat monoculture systems (Table 2 and Table 5). This difference was particularly noticeable under high-rainfall conditions at the growth stage (specifically for the 2022 and 2019 growing seasons). This result was only found under a low and moderate application of N-fertilizer. Conversely, we found that intercropping decreased the grain yield of the mixed crop over all the cropping seasons (Table 2). As a consequence of this growth stimulation, the mixed crop expressed high adaptability to acquire N from the soil, which leads to enhanced N acquisition by biomass, as well as a better protein accumulation in the grain yield (Table 3 and Table 5). Recent research studies have suggested that the interspecific competition between intercropped legumes and cereals may leads to either negative or positive effects on growth parameters, depending on actual environmental conditions such as climate, water, and nutrients availabilities, as well as cropping species and crop management [45,46]. This was in line with our results that showed either advantages (i.e., under low and moderate N-application) or disadvantages (i.e., under high N-application) for durum wheat-chickpea intercropping on growth and N acquisition when compared to a monoculture system. The increase in the aboveground biomass of intercropped species was confirmed for the chickpea and faba bean intercropped with durum wheat in low N and P soils [32,47]. Recent research studies have demonstrated that wheat–chickpea intercropping may provide growth and yield advantages thanks to efficient use of N and water resources via both functional complements and facilitation between both intercropped species [28,48].
In the durum wheat monoculture system, the growth yield and protein yield were increased by increasing the N-application from a low to high level over all rain-fed conditions. Regarding the intercropping system, similar results were found only under high rainfall conditions, i.e., the 2022 and 2020 growing seasons, while grain yield and protein accumulation were boosted only under low and moderate N-application in response to an increasing drought during the crop growth period (i.e., from the tillering to inflorescence emergence stage). Application of N-synthetic fertilizers may stimulate growth and development, but it can also lead to an early exhaustion of soil water in dry-land areas. Consequently, a higher N-fertilizer input may lead to decrease in the grain yield when compared to the grain yield obtained with a low and moderate application of N-fertilizer [30,49]. These findings are in line with our results concerning the intercropping effect on both grain yield and protein accumulation under a low rain-fed growth period. With the exception of durum wheat monoculture, no relationships were found between the water and N supply nor with their interactions with the grain and protein yield during growth periods that were characterized by limited precipitation.
The major changes in the growth and yield parameters were strongly correlated to the cumulative rainfall during the period of January to April (i.e., the tillering to inflorescence emergence stage). It is clear that the 2021 and 2020 seasons had the lowest cumulative rainfall compared to the other two seasons. The 2021 season had the lowest cumulative rainfall, followed by the 2020 season (with almost no rainfall in February). Despite the fact that the four seasons were similar in terms of cumulative rainfall, this period remained below the average annual cumulative rainfall of the past few years (315 mm). According to our results, both the LAI and GY were affected by the cropping seasons. These two parameters were mainly affected by the rain distribution. In the mixed crops, it was observed that the rainfall of the beginning of the year (January, February, March, and April) contributed to a rapid increase in the LAI, even with a low nitrogen dose (LAI = 2.4 for the 2022 season). Conversely, a cumulative rainfall of only 81 mm between January and April in the 2021 cropping season did not indicate an association, despite a nitrogen input of 100 units. Additionally, the light competition exerted by the durum wheat was thought to have reduced the refracted light absorption on the chickpea crop, resulting in a decrease of the LAI [49]. Furthermore, rainfall at the end of the cycle combined with mild temperatures contributed the most to the formation of the GY (N-60 dose in 2019 and 2022). The GY was higher for the 2020 and 2021 seasons with a N-100 mixture, implying that the impact of high N supply rates is related to the supply of rainfall [30].
The association of the two crops displayed a better stability of grain yield during the crop seasons; this was most likely due to the complementarity between the two crops. The evolution of the GY for intercropping over the years follows the same pattern as the cereal crop due to its associated competitiveness for resource acquisition [45]. Protein content was higher in the 2021 season for chickpea. Our results are in agreement with those reported by Varol et al. [50]. Indeed, a rainfall of 80 mm recorded before flowering contributed positively to the increase of protein level in the seeds. By contrast, this rate was significantly lower in 2022 due to yield losses from sparrow attacks.
The results also showed that both the NUE and WUE were globally higher for durum wheat monoculture and intercropping systems, except during the drought growth period that was reported in the 2021 growing season where they were greater for the chickpea monoculture system. Increasing N-application from a low to high dose was associated with a progressive and simultaneous increase in both the WUE and NUE. However, this was only confirmed in the intercropping system, and under optimal rainfall conditions. This may be due to too much water availability during the growth period, which permitted an efficient optimization of the excessive N-fertilizer by intercropped chickpea and durum wheat during growth and yield development. In the rain-fed cropping system, the simultaneous optimization of water and N-fertilizer inputs was generally challenging due to irregular rainfall distribution, temperature, cropping species (i.e., high competition between intercropped species) and system, as well as due to the competition between the crops and weeds [26,51]. In the conditions where the cumulated rainfall was low at the growth stage, decreasing the N-application leads to an increase in the NUE, particularly for the chickpea monoculture system. Meanwhile, no significant change was found in the WUE among all N-application × cropping system treatments. This may be explained by the negative interaction between water and N use, which leads to an increase in N losses (i.e., denitrification) through high evapotranspiration as a consequence of enhancing the WU during the 2021 growing season (Table 4). Thus, when water availability is over supplied, its interactions with N may become negative because of low or no increases in growth with respect to water and nutrient acquisition [11,52].
The simultaneous assessment of NUE and WUE in our study permits a better understanding of the growth and yield response to contrasting N-applications and rainfall distributions in both monoculture and intercropping systems. Regardless of the NNI results (Figure 2), the positive interaction between N-fertilizer and water use also leads to an enhancing of N acquisition by the intercropped species in both dry and rain-fed growth stages. Hence, the intercropping advantage in terms of biomass and N uptake by crop was confirmed in high- and low-rainfall conditions, particularly under low and moderate N-applications. A recent research study reported that high N fertilization leads to water depletion in the deep soil layers, contributing to a low NUE and WUE as a consequence of low photosynthetic activity [53].
The principal findings in this field research make it possible to define relationships between WUE and NUE over a wide range of rain-fed and N-application conditions in semiarid regions (Figure 3). The obtained results highlighted the positive relation between water and nitrogen use in mixed durum wheat-chickpea systems. We also defined, in this work study, the linear equations that describe the relationship between the WUE and NUE in both durum wheat and chickpea-durum wheat intercropping systems. These findings could be considered the first simultaneous assessment of NUE and WUE by cereal–legume intercropping. The effective use of the major results from this field research may offer the opportunity to design and co-evaluate efficient and resilient intercropping systems in terms of N and water use in semiarid Mediterranean regions.

5. Conclusions

The major finding of this field research lies in its aims to simultaneously assess the interaction between water and nitrogen use in rain-fed durum wheat-chickpea intercropping systems. We investigated a new approach through exploring the relationship between the WUE and NUE, and their possible feedback on the multiple physiological parameters such as the LAI, aboveground biomass, grain yield, and N uptake. The measurement of these parameters was further used to calculate two key indices (i.e., LER and NNI), which are commonly recommended in the diagnosis of intercropping advantage. This approach was performed under semiarid and Mediterranean conditions over four years to demonstrate the relevance of NUE and WUE co-analysis for studying N and water facilitation in intercropping systems. These must have contributed to the simultaneous optimization of N and water use in both intercropped species. Furthermore, in this study, we investigated a new model of cereal–legume intercropping, which focuses on the chickpea and durum wheat cultivated according to the conventional agricultural practices applied by farmers in the cereal-fallow rotation systems of Northeast Algeria. The results suggest that the positive interaction between N and water use by mixed crops principally leads to improved growth (i.e., LAI and aboveground biomass) and yield quality (i.e., protein yield and N-nutrition) thanks to the simultaneous increase of WUE and NUE. This was globally confirmed under low and moderate applications of N-fertilizers over all of the cropping season conditions. The nitrogen inputs from fertilization progressively enhanced only the protein production, WU, WUE, and NUE for the mixed chickpea-durum wheat, particularly under the optimal distribution of rainfall conditions (i.e., the 2022 and 2020 growing season). Moreover, intercropping advantages were confirmed in terms of biomass production and N acquisition in the intercropped species over most of the cropping seasons. However, this was not demonstrated in terms of grain yield, in which the durum wheat monoculture system was more productive than the chickpea-durum wheat intercropping system. The main findings demonstrated in this short term field research need to be followed up on by investigating the positive and negative interactions between the NUE and WUE for other models of cereal–legume intercropping, which will be adopted as innovative practices for replacing the fallow in cereal-fallow rotation under semiarid conditions.

Author Contributions

O.K.: Manuscript writing, data collection, plant and soil sampling, and laboratory analysis. N.-Y.R.: Statistical analysis, general lecture, and revision of manuscript sentences. M.S., B.Z., B.H., F.-Z.B., N.H., R.G. and A.L.: Partial contributions in data collection and plant and soil analysis. M.L.: Methodology formulation, manuscript writing, revision, supervision, field management, and data collection. All authors have read and agreed to the published version of the manuscript.

Funding

This research received financial funding from PRIMA (grant agreement no. 1912)—a program that is supported by the European Union—as well as from the research project of “Research-based participatory approaches for adopting Conservation Agriculture in the Mediterranean Area–CAMA” for the Algerian coordinator, Pr. Mourad LATATI. This work was also supported by the PRFU project (D04N01ES160320190001) run by the Algerian Ministry of Higher Education and Scientific Research (M. Latati., Research work planification). This publication was supported by the RUDN University Scientific Projects Grant System, project no. <202724-2-000> (Rebouh N.Y).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Mean monthly cumulated rainfall and mean monthly temperatures over the four studied growing seasons (GS) in the experimental site.
Figure 1. Mean monthly cumulated rainfall and mean monthly temperatures over the four studied growing seasons (GS) in the experimental site.
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Figure 2. Nitrogen nutrition index (NNI) values calculated under different treatments during both the flowering (NNI-F) and harvest (NNI-H) stages of each cropping system in the 2019 to 2022 cropping seasons. Values represent means ± standard error. No significant (p < 0.05) difference between means values that are marked with the same letter.
Figure 2. Nitrogen nutrition index (NNI) values calculated under different treatments during both the flowering (NNI-F) and harvest (NNI-H) stages of each cropping system in the 2019 to 2022 cropping seasons. Values represent means ± standard error. No significant (p < 0.05) difference between means values that are marked with the same letter.
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Figure 3. Water use efficiency (WUE) versus nitrogen use efficiency (NUE) for the chickpea and durum wheat in both monoculture and mixture cropping systems. Linear correlation was established between all the WUE and NUE values measured during the four cropping seasons and under each N-level treatment in the four replicates for each N-level × year treatment. Asterisk “*” and “***” denotes the significant difference at p < 0.05 and p < 0.001, respectively.
Figure 3. Water use efficiency (WUE) versus nitrogen use efficiency (NUE) for the chickpea and durum wheat in both monoculture and mixture cropping systems. Linear correlation was established between all the WUE and NUE values measured during the four cropping seasons and under each N-level treatment in the four replicates for each N-level × year treatment. Asterisk “*” and “***” denotes the significant difference at p < 0.05 and p < 0.001, respectively.
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Table
Table 1. Meteorological and soil physico-chemical proprieties of the experimental site. Rainfall and temperatures values are given in mm and °C units, respectively.
Table 1. Meteorological and soil physico-chemical proprieties of the experimental site. Rainfall and temperatures values are given in mm and °C units, respectively.
Soil Physico-Chemical PropertiesExperimental Site
(0–30 cm)
Clay (%)43
Loam (%)35
Sand (%)22
CaCO3 (%)22
Soil organic matter (%)1.25
Total nitrogen (g kg−1)1.33
Total phosphorus (mg kg−1)264
Available N (mg kg−1)22
Available P (mg kg−1)9.24
pH8.41
Bulk density (g cm−3)1.39
Soil water content at wilting point (m3 m−3)0.15
Soil water content at field capacity (m3 m−3)0.24
Climate characteristics
Mean of cumulated rainfall during cropping seasons (1981–2020)315
Annual mean temperature (1981–2020)14.93
Cumulated rainfall during the 2018/2019 cropping season257.22
Cumulated rainfall during the 2019/2020 cropping season259.55
Cumulated rainfall during the 2020/2021 cropping season272.25
Cumulated rainfall during the 2021/2022 cropping season274.20
Annual mean temperature during the 2018/2019 cropping season14.27
Annual mean temperature during the 2019/2020 cropping season13.15
Annual mean temperature during the 2020/2021 cropping season12.72
Annual mean temperature during the 2021/2022 cropping season16.64
Climate data were collected from the Algerian National Office of Meteorology in the Setif region. (https://www.infoclimat.fr/). Date of access was in 15 September 2022.
Table
Table 2. Grain yield (GY) and leaf area index (LAI) in durum wheat, chickpea, and mixed crop under all crop-syst N level treatments in the 2019 to 2022 growing seasons. Data are the means ± standard error of the four replicates. Mean values labeled with the same letter were not significantly different at p < 0.05.
Table 2. Grain yield (GY) and leaf area index (LAI) in durum wheat, chickpea, and mixed crop under all crop-syst N level treatments in the 2019 to 2022 growing seasons. Data are the means ± standard error of the four replicates. Mean values labeled with the same letter were not significantly different at p < 0.05.
LAI GY
(t ha−1)
Cropping systemN-level20222021202020192022202120202019
ChickpeaN-300.56 d0.20 c0.43 d0.42 d0.12 c1.84 a0.70 d0.39 d
ChickpeaN-600.90 c0.44 c0.59 d0.44 d0.17 bc1.64 ab1.27 c0.99 c
ChickpeaN-1001.03 bc0.25 c0.68 cd0.88 c0.18 bc1.60 ab0.34 d1.42 c
WheatN-302.26 ab1.84 b2.58 b1.16 c2.68 b0.89 bc3.05 b3.30 b
WheatN-601.59 b2.74 a4.01 a1.08 c4.64 a1.04 b4.62 a 3.42 b
WheatN-1001.65 b3.20 a4.31 a1.30 b4.25 a1.37 b5.02 a4.21 a
Mixed cropN-302.40 a1.62 b1.51 c1.45 b1.04 c0.59 c1.03 c0.88 c
Mixed cropN-601.39 bc1.01 bc0.93 cd1.49 b1.85 bc0.83 bc1.25 c1.62 c
Mixed cropN-1002.01 ab1.41 b0.78 cd2.22 a2.08 bc0.50 c2.74 bc1.16 c
p valueCropping≤0.001≤0.001≤0.001≤0.001≤0.001≤0.001≤0.001≤0.01
N-level0.02≤0.001≤0.001≤0.0010.030.99≤0.010.51
Crop × N-level≤0.01≤0.001≤0.001≤0.0010.160.26≤0.0010.96
Table
Table 3. Protein yield and nitrogen use efficiency (NUE) in the chickpea, durum wheat, and mixed crops for each crop-syst N level treatment in the 2019 to 2022 growing seasons. The data represents the means ± standard error of the four replicates. No significant difference (p < 0.05) was found between the mean values within the same letter.
Table 3. Protein yield and nitrogen use efficiency (NUE) in the chickpea, durum wheat, and mixed crops for each crop-syst N level treatment in the 2019 to 2022 growing seasons. The data represents the means ± standard error of the four replicates. No significant difference (p < 0.05) was found between the mean values within the same letter.
Protein Yield
(kg ha−1)		 NUE
(kg kg−1)
Cropping systemN-level20222021202020192022202120202019
ChickpeaN-3015.12 c438.47 a120.85 cd68.05 a0.04 c1.65 a0.60 c0.11 a
ChickpeaN-6028.83 c276.25 ab267.90 c133.84 a0.05 c0.61 b0.69 bc0.16 a
ChickpeaN-10017.94 c359.94 a67.20 d253.13 a0.02 c0.52 b0.12 d0.24 a
WheatN-30243.49 ab138.2 bc408.85 b619.54 a0.66 a0.51 b2.05 a0.98 a
WheatN-60340.62 a181.61 b495.34 b630.26 a0.61 a0.40 b1.28 b0.77 a
WheatN-100338.80 a256.18 b610.50 a731.31 a0.42 b0.36 b0.96 b0.68 a
Mixed cropN-30104.6 bc144.66 bc155.04 cd164.16 a0.28 bc0.34 b0.48 c0.26 a
Mixed cropN-60141.22 b128.70 bc169.18 cd308.76 a0.40 b0.26 bc0.44 c0.47 a
Mixed cropN-100161.65 b91.04 c288.05 c221.90 a0.57 a0.13 c0.63 bc0.21 a
p valueCropping≤0.001≤0.001≤0.001≤0.001≤0.001≤0.001≤0.001≤0.001
N-level0.050.230.020.560.12≤0.001≤0.0010.87
Crop × N-level0.590.040.030.930.04≤0.01≤0.010.76
Table
Table 4. Water use (WU) and water use efficiency for grain yield (WUEGY) in the chickpea durum wheat and mixed crop systems under different crop N-level treatments in the 2019 to 2022 growing seasons. Data are the means ± standard error of the four replicates. Mean values labeled with the same letter were not significantly different at p < 0.05.
Table 4. Water use (WU) and water use efficiency for grain yield (WUEGY) in the chickpea durum wheat and mixed crop systems under different crop N-level treatments in the 2019 to 2022 growing seasons. Data are the means ± standard error of the four replicates. Mean values labeled with the same letter were not significantly different at p < 0.05.
WU (m3 ha−1) WUEGY (kg m−3)
Cropping systemN-level20222021202020192022202120202019
ChickpeaN-303197.04 a4190.34 a2981.84 b3307.30 b0.04 c0.43 a0.24 d0.12 c
ChickpeaN-603106.66 ab4199.88 a3007.83 b3325.92 ab0.05 c0.39 ab0.42 c0.30 b
ChickpeaN-1003023.24 b4340.05 a3043.97 ab3292.01 b0.06 c0.36 ab0.11 d0.43 b
WheatN-303231.84 a4232.43 a3076.84 ab3364.21 a0.84 b0.21 bc0.99 b1.02 a
WheatN-603125.38 ab4185.35 a3123.34 a3312.01 ab1.49 a0.25 bc1.48 a1.04 a
WheatN-1002906.51 c4325.37 a3089.14 ab3217.23 c1.41 a0.31 b1.63 a1.30 a
Mixed cropN-303244.64 a4191.54 a3095.65 ab3355.61 a0.32 bc0.16 c0.35 d0.26 b
Mixed cropN-603048.16 b4211.84 a2997.36 b3381.01 a0.48 bc0.17 c0.37 d0.42 b
Mixed cropN-1003013.01 b4321.84 a3083.33 ab3479.09 a0.69 b0.11 d0.79 bc0.33 b
p valueCropping0.670.97≤0.010.01≤0.001≤0.001≤0.001≤0.001
N-level≤0.001≤0.010.190.900.010.98≤0.0010.49
Crop×N-level0.030.790.020.030.050.28≤0.0010.95
Table
Table 5. Land equivalent ratio (LER) values for grain yield (LERGY) and nitrogen uptake by grain yield (LERNY). The total biomass (LERTB) and LER for nitrogen uptake by biomass (LERNB) was calculated in the 2019 to 2022 cropping seasons under the three nitrogen fertilizer doses. Values represent means ± standard error. No significant (p < 0.05) difference between means values that are marked with the same letter.
Table 5. Land equivalent ratio (LER) values for grain yield (LERGY) and nitrogen uptake by grain yield (LERNY). The total biomass (LERTB) and LER for nitrogen uptake by biomass (LERNB) was calculated in the 2019 to 2022 cropping seasons under the three nitrogen fertilizer doses. Values represent means ± standard error. No significant (p < 0.05) difference between means values that are marked with the same letter.
Cropping SeasonN-LevelLERGYLERNYLERTBLERNB
Season: 2019N-300.88 ab1.01 b1.20 b1.56 ab
N-601.22 a1.65 a1.44 a1.91 a
N-1000.45 c0.50 cd0.86 b0.78 c
Season: 2020N-300.48 c0.49 cd0.48 d0.44 d
N-600.36 c0.39 d0.26 d0.22 d
N-1000.80 b0.75 bc0.31 d0.28 d
Season: 2021N-300.57 bc0.60 cd1.19 b1.71 ab
N-600.57 bc0.51 cd1.01 b1.25 b
N-1000.35 c0.31 d1.12 b1.39 b
Season: 2022N-300.55 bc0.55 cd1.05 b1.02 c
N-600.62 bc0.67 c0.69 c0.59 c
N-1000.62 bc0.65 c0.69 c0.61 c
p valueSeason≤0.001≤0.001≤0.001≤0.001
N-level0.10≤0.0010.040.01
S × N-level≤0.001≤0.0010.050.01
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MDPI and ACS Style

Kherif, O.; Haddad, B.; Bouras, F.-Z.; Seghouani, M.; Zemmouri, B.; Gamouh, R.; Hamzaoui, N.; Larbi, A.; Rebouh, N.-Y.; Latati, M. Simultaneous Assessment of Water and Nitrogen Use Efficiency in Rain-Fed Chickpea-Durum Wheat Intercropping Systems. Agriculture 2023, 13, 947. https://doi.org/10.3390/agriculture13050947

AMA Style

Kherif O, Haddad B, Bouras F-Z, Seghouani M, Zemmouri B, Gamouh R, Hamzaoui N, Larbi A, Rebouh N-Y, Latati M. Simultaneous Assessment of Water and Nitrogen Use Efficiency in Rain-Fed Chickpea-Durum Wheat Intercropping Systems. Agriculture. 2023; 13(5):947. https://doi.org/10.3390/agriculture13050947

Chicago/Turabian Style

Kherif, Omar, Benalia Haddad, Fatma-Zohra Bouras, Mounir Seghouani, Bahia Zemmouri, Ramzi Gamouh, Nadia Hamzaoui, Amira Larbi, Nazih-Yacer Rebouh, and Mourad Latati. 2023. "Simultaneous Assessment of Water and Nitrogen Use Efficiency in Rain-Fed Chickpea-Durum Wheat Intercropping Systems" Agriculture 13, no. 5: 947. https://doi.org/10.3390/agriculture13050947

APA Style

Kherif, O., Haddad, B., Bouras, F. -Z., Seghouani, M., Zemmouri, B., Gamouh, R., Hamzaoui, N., Larbi, A., Rebouh, N. -Y., & Latati, M. (2023). Simultaneous Assessment of Water and Nitrogen Use Efficiency in Rain-Fed Chickpea-Durum Wheat Intercropping Systems. Agriculture, 13(5), 947. https://doi.org/10.3390/agriculture13050947

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