Role and mechanism of green manure in driving the nitrogen cycle of the crop-soil-environment system

Planting and utilizing green manures is a crucial measure for regulating the nitrogen cycling in farmland. This measure involves multiple processes such as nitrogen fixation, mineralization, nitrification, denitrification, and uptake and utilization. All of which are essential for maintaining the stability and functionality of agricultural ecosystems. This paper systematically reviews the roles and mechanisms of green manure driving nitrogen (N) cycling in the crop-soil-environment system from three perspectives: N input, storage, and output. In terms of N input, it explores the symbiotic nitrogen-fixing potential of leguminous green manures and its responses mechanisms to factors such as nitrogen fertilization application, water availability, and cropping patterns. Additionally, the mechanisms by which rhizosphere microbial community structure and metabolic activities of green manures drive soil autotrophic nitrogen fixation were analyzed. Regarding N storage, it summarizes the effects of green manure on enhancing the soil nitrogen pool through regulating soil mineralization and priming effect, thereby altering the composition and storage of organic and inorganic nitrogen pools. For N output, it summarizes how green manure, through practices like chemical fertilizers substitution , mix sowing, and the co-application of straw or amendments, regulate soil ammonification, nitrification, and denitrification. This regulation effectively reduces gaseous nitrogen losses such as ammonia volatilization and nitrous oxide emissions through microbial mechanisms. It also outlines pathways for mitigating nitrate leaching risk by optimizing green manure species selection and cropping systems, leveraging root regulation and soil structure improvement. Furthermore, it reviews the contributions of green manure to the nitrogen supply of main crops. Its also explores how green manure enhances nitrogen uptake and the utilization efficiency through optimizing soil nitrogen nutrient availability. Future research should focus on the following directions: 1) developing stress-resistant and high efficiency nitrogen-fixing green manure germplasms; 2) analyzing and regulating nitrogen-fixing potential of leguminous green manure at regional scales; 3) innovating technologies and regulatory products that enhance nitrogen fixation efficacy; 4) elucidating the mechanisms by which green manure input regulates soil nitrogen priming effects and functional microbial communities. Addressing these research themes will establish a robust theoretical foundation for systematically improving nitrogen cycling and utilization efficiency in agricultural systems.