Nitrogen Mineralization of Mature Chinese Milk Vetch, and the Effect of Incorporated Mature Chinese Milk Vetch on Nitrogen Uptake and Yield of Rice on a Gley soil

Chinese milk vetch (CMV) (Astragalus sinicus L.) at flowering-stage is a green manure traditionally used as alternative basal nitrogen in paddy rice fields. In order to evaluate the nitrogen availability of mature-stage CMV, compared with the flowering-stage CMV, we carried out field cultivation and incubation studies using ill-drained Gley soil with either mature-stage CMV incorporated. The results showed that mature-stage CMV provided less available nitrogen for early rice growth than the fresh flowering-stage CMV, resulted in lower panicle number and hence lower total grain number of rice. Contrary to our expectation, which mature-stage CMV replace nitrogen topdressing due to the prolonged nitrogen mineralization, the small amount of the mineralized nitrogen was insufficient to support the rice growth. Nevertheless, rice cultured with the mature-stage CMV achieved a yield over 450 g m-2, without the use of agrochemicals. Mature-stage CMV was suggested to be potentially applicable under ill-drained soil conditions, if applied heavily.