The Effect of Nitrogen Supply on Water and Nitrogen Use Efficiency by Wheat–Chickpea Intercropping System under Rain-Fed Mediterranean Conditions

It is well known that legume–cereal intercropping systems are more efficient in terms of resources use, in particular nitrogen (N) and water. However, the response of this cropping system to water and N co-limitation was poorly studied in most of the recent field researches. The present study aims to assess the relationship between N and water use efficiency (NUE and WUE) by chickpea–durum wheat intercropping under contrasted climate and N supply conditions. Field experiments were carried out during the 2021/2022 growing season, in three sites located at both sub-humid and semi-arid regions. WUE, NUE, aboveground biomass, grain yield and crop physiological parameters for either intercropped chickpea or durum wheat were assessed and compared to the respective measurements in monocultures among all N-fertilizer level × site treatments. The results showed that WUE relative to grain yield (WUE_GY) and biomass (WUE_YB) were significantly higher in sole cropped wheat under the conditions of the three studied sites, except for WUE_YB in S2, in which intercropping increased WUE_YB by +0.46 and +1.03 kg m⁻³, as compared respectively, to monoculture under low application of N fertilizer. As compared to chickpea monoculture, intercropping increased WUE_GY by more than 0.30 and 0.57 kg m⁻³ under semi-arid conditions (S1 and S3) over three N-application doses, and by more than 0.18 kg m⁻³ under sub-humid conditions (S2). Simultaneously, NUE was significantly increased by intercropping, where in the mixed crop the highest values were noted as compared to sole-cropped durum wheat and chickpea. However, reducing the N-application dose leads to a gradual increase in NUE by more than 4.44 kg kg⁻¹. As a consequence, intercropping enhanced protein accumulation in the grain yield of mixed crops by more than 30 kg ha⁻¹ as compared to sole-cropped durum wheat, in particular under moderate N-application and sub-humid climate. Indeed, average chlorophyll content was increased (7.8%) in intercropped durum wheat under all applied N-doses in sub-humid conditions. Rain-fed chickpea–wheat intercropping promotes an improvement in growth and yield quality thanks to simultaneous optimization of water and N use under low and moderate N-application in both semi-arid and sub-humid climates.