Natural Reseeding of Chinese Milk Vetch(Astragalus sinicus L.) as a Source of Green Manure On Rice in Southern Korea.

Natural Reseeding of Chinese Milk Vetch(Astragalus sinicus L.) as a Source of Green Manure on Rice in Southern Korea Sang-Yeol Kim, Seong-Hwan Oh, Woon-Ha Hwang, Sang-Min Kim and Hang-Won Kang 1Functional Crop Resource Development Division, Department of Functional Crop, National Institute of Crop Science, RDA, Milyang 627-803, Korea Chinese milk vetch(Astragalus sinicus L) is the most widely-used green manure on rice crop in southern Korea but the seed is planted annually. In order to develop a natural reseeding technology, the optimum soil incorporation time of Chinese milk vetch(CMV) plant residues, seed persistence in soil, biomass production and subsequent rice yield were determined from 2005 to 2008. Generally, insufficient seedling stand was regenerated with CMV incorporation to the soil at 20 and 25 days after flowering (DAF), while high regeneration(i.e. > 400 seedlings per m2) was observed at 35 and 40 DAF. High reseeding stand of CMV incorporated at 35 DAF or later was related with high seed viability and heavy seeds. Sufficient number of CMV seeds remained in soil for 4 months and a good number of CMV seedlings were regenerated from this seed bank at rice harvest time in fall. The natural reseeding stand for the 3-year trials was stable ranging from 565 to 804 plants per m2 and the biomass production was sufficient to supply nitrogen requirement for rice growth. As a result, the use of reseeding CMV plant can produce similar rice yield like that of rice mono cropping at 9kgN/10a. Natural reseeding technology offers several advantages compared to the annual CMV seeding like reduction of rice production cost, greater survival during winter and reduction of chemical nitrogen fertilizer use. These results indicate that natural reseeding technology is beneficial and thus could be applied in CMV-rice cropping system in the southern parts of Korea.