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.