Effects Of Moldboard Tillage In Winter On Double Rice Yield,the Quality Of Paddy Standing Water And Greenhouse Gas Emissions Under Straw Retention

Rice is one of the most important food crops in China.As a result of long-term simplified tillage,soil fertility in rice fields decreases,returning straw to fields is difficult,and,which seriously jeopardizes the increase of rice yield.Straw return to the field can change soil fertility and increase crop yield.On the other hand,straw return to fields will also lead to increased greenhouse gas emissions and the change of the quality of paddy standing water.Therefore,it is of great significance to improve the rice yield and improve the environmental quality of rice field through tillage innovation under straw incorporation.Thus,in this study,through a two-year field experiment,three tillage treatments were set up in winter:no-tillage in winter fallow（CK）,moldboard tillage annually（MTA）,and moldboard tillage only once（MTO）under straw retention.The effect of different tillage on the grain yield,aboveground biomass,environmental quality in standing water,and greenhouse gases emission were investigated.The main findings are as follows:Compared to CK,the yield of early rice in the second year was significantly increased by 3.78%by moldboard tillage in winter.Moldboard tillage tended to increase the yield in the first year for early rice and in the second year for late rice,but the differences were not significant.The positive effect of moldboard tillage in the first year on the yield of early rice still persisted in the second year.As to the yield composition,the spikelet number per panicle for early rice in the second year was significantly increased by 11.5%by MTO compared to CK,and the effect of moldboard tillage would still exist in the second year.There was no significant effect on the spikelet number by MTA and MTO.The number of panicles,1000-grain weight and grain filling were not significantly affected by any treatment.The dry matter weight of early rice in the first year was significantly increased by MTA and MTO,while that of late rice was not affected.In the second year,MTA significantly increased the dry matter weight of both early and late rice,but MTO had no significant effect.There were no significant effects of MTA and MTO on the uptake of N,P or K.The N uptake of early rice in the second year was significantly increased,while that of late rice was not affected under MTA and MTO.There were no significant effects of MTA and MTO on the uptake of P in the second year.But MTA significantly increased K uptake of both early and late rice in the second year.No evident effect of MTA and MTO was observed on the average concentration of total organic carbon（TOC）in the standing water in the second year;however,the average concentration of total nitrogen（TN）of in the early rice season was significantly increased.MTA and MTO lowered the average total phosphorus（TP）concentration in both early and late rice season in both years,but only significantly in the first year.Compared to CK,MTA and MTO significantly reduced the accumulated CH₄ emissions as well as GWP and GHGI in the late rice season in both years.The effects of MTA and MTO on the cumulative N₂O emissions were significant only in the late rice season in the first year.MTA and MTO significantly reduced the accumulative CH₄ emissions,GWP and GHGI in the first year,but no significant effect was found in the second year.Therefore,moldboard tillage can significantly increase the yield,biomass,and N uptake of early rice.Meanwhile,moldboard tillage could decrease CH₄ emissions,global warning potential（GWP）and greenhouse gas intensity（GHGI）in both late rice season and the while year.The mitigation effect of winter moldboard tillage on CH₄ emissions could persist at least over 2 years.The long-term effect of moldboard tillage on soil properties and greenhouse gas emissions still need to be examined in the double rice cropping system.