Crop Production And Greenhouse Gas Mitigation Through Optimized Farming Practices In Northern China Plain

Northern China Plain（NCP）is one of the most important grain production regions in China.The wheat-maize rotation system is widely implemented in this region.In recent years,excessive amount of water and fertilizers have been put into soils to achieve high crop yield.These inputs could really achieve the high grain yields,but also increased greenhouse gas emissions.Therefore,it is necessary to maintain high grain yields together with low greenhouse gas emissions while mitigating the water and N resources to ensure the sustainable development of agriculture in this region.To resolve the challenges mentioned above,two long-term field experiments were conducted from 2008（Experiment 1）and 2012（Experiment 2）,respectively.Experiment 1 includes seven treatments:Convention（CON）,Optimum（OPT）,No-Tillage（NT）,Water Saving I（WSI）,Water Saving Ⅱ（WSⅡ）,Water Restoration（WR）and Organic Farming（ORG）,by taking into account multiple factors covering cropping system,water and nitrogen management,straw management and tillage systems.Experiment 2 includes five treatments:No N fertilizer（CK）,Urea only（U）,Urea with nitrification inhibitor（NI）,Urea with urease inhibitor（UI）,Urea with combined nitrification inhibitor and urease inhibitor（NIUI）.Firstly,we systematic researched the effects of different planting patterns on crop yield,water and N utilization and greenhouse gas emissions by the measurements in situ.Secondly,we systematic researched the effects of nitrification and urease inhibitors on crop yield,N utilization and N₂O emissions in situ.Thirdly,we elucidate the producing pathways of nitrous oxide from this rotation system in situ.The results found that:（1）Compared with CON treatment,the other treatments could effectively reduce water and nitrogen input and improve water and nitrogen use efficiency.When the six years rotation cycle under consideration,compared to CON treatment,OPT and NT reduced N fertilizer and groundwater inputs by 44%and 43%respectively,but not decreased crop yield an,and improved nitrogen and water use efficiency by 69-75%and 43-48%respectively.Compared to CON treatment,WSI,WSⅡ,WR and ORG treatments decreased N fertilizer and groundwater inputs by 56-79%and 46-64%respectively,and increased nitrogen and water use efficiency by 69-75%and 43-48%respectively.OPT and NT treatment had similar crop yields as CON treatment,whereas the WSI,WSII,WR and ORG treatments significantly reduced the crop yields by 22-61%compared with CON treatment（2）Compared with CON treatment,the other treatments could effectively reduce N₂O emissions,NGWP and GHGI.In the present study,we found that OPT,NT,WSⅠ,WSⅡ,WR and ORG reduced annual N₂O emissions by 29%,30%,33%,40%,23%and 41%,respectively;decreased NGWP by 31%,33%,46%,52%,48%and 61%;lowered GHGI 30%,31%,34%,32%,6%and 32%.N20 emission,N fertilizer production and power for irrigation were the top three contributors to NGWP,with shares of 15-22%,24-45%and 23-45%of total emissions.Soil acted as a sink for CH4,which can be neglected in the estimation of NGWP because it represents less than 1%of NGWP.（3）Nitrification inhibitor（DMPP）exhibited a remarkable effect on the mitigation of N₂O emission and led to a high crop yield,but its efficacy was alleviated if applied together with urease inhibitor（NBPT）.Compared with U treatment,NI,NIUI and UI mitigated the cumulative N20 emissions by 55%,40%and 21%in the maize season,and 47%,40%and 33%in the wheat season.NIUI,NI and UI treatment increased the annual crop yield（7%,6%and 4%）and the N use efficiency（15%,10%and 7%）over U treatment.（4）Isotopomer analysis revealed that in N-fertilized treatment,nitrification account-ed for max.40%N₂O emissions peaks observed after fertilization and irrigation events,while nitrifier denitrification pathway was likely to be the main source that accounts for the rest of N20 emissions.The high effectiveness of nitrification inhibitor on mitigating N20 emission maybe attributed to the double inhibition effect on nitrifier denitrification.