Organic nitrogen nutrition affects biochemical characteristics, water use efficiency and yield of intercropped barley-chickpea under water stress

Intercropping and nitrogen (N) management may represent two effective approaches to mitigate the possible effects of water stress. A 2-year field study was conducted to investigate the effects of different N management systems on the biochemical and physiological characteristics, yield, and water use efficiency (WUE) of intercropped barley ( Hordeum vulgare L.) and chickpea ( Cicer arietinum L.) under water stress during the 2019-20 and 2020-21 growing seasons. The treatments consisted of two irrigation regimes (normal irrigation and irrigation cut-off at the end of flowering), two cropping systems (sole cropping and barley–chickpea intercropping, 1:1 ratio) and three N management systems: organic N nutrition (20 t ha⁻¹ of sheep manure + Azospirillum brasilense ), integrated N nutrition (10 t ha⁻¹ of sheep manure + 60 kg N ha⁻¹ + Azospirillum brasilense ), and chemical N nutrition (120 kg N ha⁻¹). Regardless of other treatments, water stress significantly reduced most parameters—including grain yield by up to 58.8% in barley and 63.0% in chickpea—except for catalase and peroxidase activities. However, these declining trends were mitigated when organic N nutrition and intercropping were applied. Intercropped chickpea increased chlorophyll b and total chlorophyll content by 32.1 and 52.3%, respectively, compared to sole cropping under water stress. Catalase and peroxidase activities in both crops increased under water stress, particularly under chemical N nutrition in both cropping systems. In intercropping conditions, water stress increased WUE by 1.4% in integrated treatment and by 34.8% in organic, compared to normal irrigation. Overall, considering environmental and climate change concerns, especially in arid climates, barley-chickpea intercropping combined with organic N nutrition can mitigate the severity of water stress and improve grain yield and WUE.