Covering green manure increases rice yields via improving nitrogen cycling between soil and crops in paddy fields

Building soil organic nitrogen (SON) pools and improving N cycling between soil and crops can reconcile the global need for increased food production and environmental sustainability. We combined a global database and a 40-year field experiment in South China to demonstrate the beneficial effects of traditional green manure on rice yield and soil N cycling in paddy ecosystems. Covering green manure increased rice yield by up to 24 % in China and by 25 % globally mainly due to activated microbial activity, increased SON cycling, and available N content, compared with winter fallow treatment. Soil catabolic processes, such as enzyme activities were stimulated, thus increasing the rate of gross protein depolymerization by 2.3–3.8 times. This led to an increase in the amount of active SON fractions, e.g. of hydrolyzable amino acid N by 32 %–44 %. Concurrently, green manure increased the rate of gross amino acid consumption by microorganisms by 1.1–2.0 times. One part of the N ingested by microorganisms was used for growth to increase microbial biomass N and subsequently dead residues, and the other part increased soil NH₄⁺-N content through catabolism. Ultimately, the utilization of soil original N by rice plants was improved by 31 %–42 % under covering green manure treatments. This study provides an agricultural management strategy to improve soil N supply for crops by increasing organic N cycling in paddy ecosystems and thus saving mineral N fertilizer.