Effect of seedling transplanting date on methane emission from rice paddy soil during cultivation

In most temperate mono-rice cultivation systems like Korea, the local recommended transplanting date of rice (Oryza sativa L.) seedlings is proposed by the government agency considering climate, rice cultivar, rice productivity and quality, etc. Recently the transplanting of rice seedlings earlier than the recommended transplanting date (RTD) has been adopted by the local farmers to get high yield and to harvest earlier for higher market value. Earlier transplanting than RTD might influence methane (CH4) emission due to the prolonged cultivation period, but its effect was not evaluated well so far. In this study, the effects of seedling transplanting date on CH4 emission and rice productivity were investigated for two years in a general paddy soil. The 30-day old seedlings were transplanted on the local RTD (every June 15) as the control, and at 30 and 15 days before and 15 days after the RTD for comparison. There was no difference on CH4 flux pattern among the treatments, but the earlier transplanting before the RTD significantly (P ≤ 0.05) increased total CH4 emissions during rice cultivation due to the extended soil flooding period and improved plant growth. Rice grain yield was increased by earlier transplanting, but the values were not significantly different from those of transplanting practices on RTD and 15 days before RTD. Therefore, among all the treatments, the lowest total CH4 emission per grain yield was observed in the RTD treatment. Conclusively, rice transplanting following the RTD, rather than early or late transplanting, could be more effective to minimize CH4 emission without significantly decreasing the rice productivity.