The Effect Of First Flood Irrigation Timing After Sowing On Yield And Water Productivity Of Dry Direct-seeded Rice

Water resources shortage, rural labors deficit, the huge greenhouse gas(GHG) emissions from rice field and the low mechanization level in raising rice seedling and transplanting of traditional rice planting restrict the development of rice production in China. Compared with transplanted rice, dry direct-seeded rice(DDSR) conserves a greater amout of water and is less labor intensive during the rice seedling nursery and transplantion phase and produce less GHG emissions throughout all growth stages. Now the classical transplanted-flooded rice transplanting mechanization is still backward in our country, while DDSR is relatively easy to realize completely mechanized rice production. Studies indicate that the grain yield of DDSR which kept flooding during the whole growth period is identical to grain yield of transplanted-flooded rice. But the grain yield of DDSR was decreased significantly in rain-fed system. Therefore, we found that one of the important facters affecting the grain yield of DDSR is the initial irrigation time after sowing. To decreasthe number of irrigation procedures and minimize the consumption of irrigation water without affecting grain yield of DDSR. It is imperative to determine the optimal time to start flood irrigation after DDSR sowing. In this experiment, four rice cultivars were used and they were planted widely as lowland transplanted rice. In order to study the response of DDSR to different initial flooding time and analysis the reasons, we measured grain yield and its components, water consumed, water productivity, greenhouse gas emission and scanned the root system of DDSR in heading stage.The results indicated that the grain yields under DDSR were not affected by the different flooding time when the initial flooding time is between 15 days to 45 days after sowing. However, when the initial flooding time is further delayed to 55 days after sowing, the yields were significant decrease. And the yield reduction caused by a delay of first flood irrigation was attributed to the decreased spikelets per m2. Study also found that delaying the first flood irrigation time after sowing conserved water and significantly increased water productivity under DDSR. Prolonging the first flood irrigation time after sowing markedly decreased the CH4 gas emission, although delaying the first flood irrigation time increased the N2 O gas emissions, the global warming potential was significantly reduced. The data of root shows that root length and number of root tips in deep soil layer at heading stage increased with delaying the first flood irrigation time after sowing.Results of the two years’ experiments show that the first flood irrigation time can be postponed under DDSR to 45 DAS in areas of central China that receive precipitation were higher than 321 mm during the 60 DAS. And that can minimize the amount of rice irrigation water, increase water use efficiency and reduce greenhouse gas emission without significant reduction in rice yield.