The fate of nitrogen derived from green manure and its influence on crop N agronomic performance

Abstract

Substituting synthetic nitrogen (N) with green manure (GM) is a sustainable agricultural practice. However, the role of GM nitrogen (GMN) in crop productivity and its environmental impact have not been well summarized. Furthermore, the mechanisms driving GMN use efficiency in response to field management, climatic conditions, and soil properties remain unclear. Therefore, this study conducted a comprehensive data synthesis on tracing ¹⁵N-labelled GM in succeeding crops, soil, and losses, combined with a meta-analysis on N agronomic performance (N uptake, N use efficiency, and partial factor productivity) after green manuring. The results showed that the recovery of N derived from GM (NdfGM) in crops, soil, integrated crop-soil system and total loss were 24.5 %, 45.9 %, 70.4 % and 29.6 % respectively, and the GMN ratio of the total N input (GMN plus chemical or organic N) primarily determined their variations. In addition, a GMN ratio above 50 % of the total N input decreased NdfGM recovery and increased losses. According to the meta-analysis results, green manuring practices increased N uptake, N use efficiency, and partial factor productivity (percentage ratio of crop yield to applied N). Adopting GMN substitution for chemical N, applying a mix of legume and non-legume GM, or increasing the GM application duration resulted in a better N agronomic performance of succeeding crops compared to that of synthetic N management. In addition, a higher N uptake was observed when incorporating GM than with the surface application method, while N use efficiency was negatively correlated with the N application rate. This study refined the current understanding of the fate of NdfGM in crop-soil systems and elaborated on the efficacy of green manuring on crop N agronomic performance. Future adoption of green manuring should pay more attention to selecting appropriate GM species combinations and optimizing GMN application rates to enhance N utilization efficiency and reduce N losses.