Effect of Chinese milk vetch (Astragalus sinicus L.) as a green manure on rice productivity and methane emission in paddy soil

This field study was undertaken to investigate the optimum recycling rate of the above ground biomass of Chinese milk vetch (Astragalus sinicus L. hereafter, vetch) to improve rice productivity and decrease seasonal methane (CH4) flux in mono-rice cultivation system. The above ground part of vetch was applied in paddy field at rates 0, 10, 20 and 40 Mg ha−1 on fresh weight basis to investigate its effect on rice (Oryza sativa) productivity and CH4 emission flux and was compared with the typical standard NPK chemical fertilization (N–P2O5–K2O = 90–45–58 kg ha−1). Rice productivity increased significantly with increasing vetch application, and more interestingly, similar grain yield was obtained between vetch application at 10 Mg ha−1 as green manure and NPK fertilization. Methane emission rates, which were measured by closed-chamber method, increased significantly (p < 0.05) with increasing application levels of vetch, and seasonal CH4 fluxes exceeded to that in NPK fertilization at over 10 Mg ha−1 vetch application. Our findings revealed that 10 Mg ha−1 vetch application as green manure amendment can be an effective application level of sustaining rice productivity without increasing CH4 emission compared to NPK fertilization in Korean mono-rice cultivation systems.