Understanding the Response of Wheat-Chickpea Intercropping to Nitrogen Fertilization Using Agro-Ecological Competitive Indices under Contrasting Pedoclimatic Conditions

Wheat-chickpea intercrops are not well studied, despite the importance of these two species in increasing agricultural profitability and ensuring nutritional and food security. The present study aims to assess the intercropping arable system's services under contrasting field management and climate conditions. Simultaneously, this assessment focuses on the most agronomic and ecological indices widely used in the literature. Durum wheat (Triticum turgidum durum L.cv. VITRON) and chickpea (Cicer arietinum L.cv. FLIP 90/13 C) were cultivated, both in sole crop and intercrop during the 2018/2019 growing season. A field experiment was carried out under controlled conditions at three contrasting pedoclimatic sites and under three levels of N fertilization. Both grain and N yield of mixture crop were significantly higher (+11%) when chickpea and durum wheat were grown together under either low or moderate N application. Soil N availability as compared to the critical level increased by more than 19% from flowering to harvest stage for intercropped wheat under low N application (N-30 and N-60), while it decreased significantly for intercropped chickpea. In rich N soils and under low rainfall conditions (site 1 and 3), intercropping was generally more advantageous for yield (+14%), N yield (+23%), and land use (103 and 119.5% for grain and N yield, respectively) only with reduced N fertilization as assessed using both land equivalent ratio (LER) and land-use efficiency (LUE). Competition dominance was directly affected by changes in climatic conditions over sites; intercropped wheat was more competitive than their respective chickpea under low rainfall conditions. These findings illustrate the crucial role of competitive index assessment in intercropping to promise a robust method for crop N and yield diagnosis during fertilization decision-making

The first calibration and evaluation of the STICS soil-crop model on chickpea-based intercropping system under Mediterranean conditions

Soil-crop models are widely used as valuable tools to assess the combined effects of cropping practices, soil management and climate on the agro-environmental indicators. They provide a wide range of predictive information that are useful to design and evaluate innovative cropping systems. However, intercropping modeling is still under development, especially for grain legumes-based intercropping system. We performed here the first calibration of the STICS (v 9.2) model on chickpea grown under contrasting nitrogen (N) levels during two copping seasons (2018/2019 and 2019/2020). This calibration allowed us to simulate a wide range of agronomic scenarios (climate, N-fertilization and cropping system) to optimize intercrops (durum wheat-chickpea) management. 37 parameters were estimated by using a sequential optimization method. Our results showed that STICS performs well in predicting Leaf Area Index (LAI), above ground biomass (AGB) and N uptake (AGPN) for both intercropped and sole cropped species, with satisfactory model efficiency (EF ranged from 0.62 to 0.93). In addition, grain yield was correctly predicted by the model with small error (NRMSE≤13%) especially for wheat crop (EF≥0.50), while it was less correctly predicted for chickpea crop (EF≤0.24 and NRMSE≤21%). STICS predicted well root depth under the conditions of our field study (EF ≥ 0.65 and NRMSE ≤ 37%). For soil outputs variables, the model simulated adequately soil water content with a satisfactory model efficiency (EF ≥ 0.65) and low relative error (NRMSE ≤. 8.8%) especially for sole cropped and intercropped chickpea. The soil N stocks were less adequately predicted (EF ≤ 0.28) with high relative error (NRMSE ≥ 56%) in sole cropping system, while it was moderately adequately predicted (EF ≤ 0.44) in intercropping. Under the two contrasted years and N-application conditions of this study, the temporal dynamic was well reproduced by the model for both plant and soil outputs with low simulation errors. RMSE values were lesser than 0.6 m2m-2 (9%), 0.2 t ha-1 (14%) and 30 kg ha-1 (12%), respectively for LAI, grain yield and AGPN of sole cropped chickpea. The dynamic of soil water content was also well reproduced among all N-application rate and during the two cropping year, with RMSE equal to 27 mm (<10%). The present work provides the first calibration for chickpea sole crop and an evaluation for durum wheat-chickpea intercrops, which will allow to use the STICS model to simulate scenarios of innovative cropping practices based on crop diversification (i.e. grain legumes and cereals) and N-fertilization management. © 2021 Elsevier B.V