Effect of legume inclusion on nitrogen fixation and subsequent crop performance in cereal-based systems

Abstract

Nearly 60% of cereal systems in East Asia rely solely on synthetic nitrogen, raising economic and environmental concerns. This research quantified biological nitrogen fixation (BNF) of five legume species—soybean, mung bean, groundnut, chickpea, and pigeon pea—in a rice-wheat rotation and measured their residual effect on subsequent rice. A three-year field trial (2020-2023) at Zhejiang University, Hangzhou, used a randomised complete block design with the 15N natural abundance method. Soybean fixed the most nitrogen (78.6 kg N/ha at flowering), while pigeon pea contributed the least (28.7 kg N/ha). Subsequent rice yields increased 8.3-18.7% in legume-preceded plots versus fallow controls. These results indicate legume inclusion can meaningfully reduce synthetic nitrogen demand in intensive cereal systems.