Mechanisms and regulatory pathways for increasing water and nitrogen use efficiencies by crop diversification: A review

Crop diversification plays a vital role in sustainable agriculture by enhancing ecosystem functions and improving resource efficiency. It is a key strategy to ensure food security while optimizing water and nitrogen use, addressing the challenges posed by limited resources, and supporting environmental preservation. This review synthesizes current knowledge regarding the mechanisms and regulatory pathways through which diversified cropping systems enhance water productivity (WP) and agronomic efficiency of nitrogen (AEN), and partial factor productivity of nitrogen (PFPN). It also identifies existing challenges and proposes priority directions for future research. This analysis focuses on studies of diversified cropping systems, such as intercropping, crop rotation, and multiple cropping, that enhance WP, AEN, and PFPN. We elucidate the underlying mechanisms driving these improvements by incorporating recent findings. Diversified cropping systems enhance WP, AEN, and PFPN by reducing water and nitrogen losses, improving soil physicochemical properties, regulating interspecific interactions, enhancing crop physiological performance, and stimulating beneficial microbial activity. These benefits are optimized through strategic crop combinations, integrated water–nitrogen management, improved tillage and mulching practices, and precision monitoring and decision-support systems. Despite these advantages, challenges remain in crop variety selection, mechanization, and the comprehensive evaluation of socio-economic and ecological outcomes. Future research should emphasize system adaptability to climate variability, the molecular mechanisms underlying water and nitrogen use, water–carbon–nitrogen coupling, artificial intelligence (AI)-assisted system design, and implementation-oriented strategies. The efficacy of diversified systems and associated management practices is strongly influenced by local climatic conditions, soil properties, and socio-economic constraints. This review highlights the need for an integrated framework combining agronomic, physiological, and molecular perspectives to better understand and regulate how crop diversification enhances WP, AEN, and PFPN. The findings provide a theoretical and technological foundation for promoting diversified, resource-efficient, and climate-resilient cropping systems, particularly in irrigated regions of Northwest China and similar climatic environments.