Effects Of Water And Nutrient Regulation And Biochar Application On Crop Yield,Nitrogen And Phosphorus Use Efficiency And Nitrogen And Phosphorus Leaching

Winter wheat/summer maize cropping system is the main planting pattern in northern China,but excessive fertilization and unreasonable irrigation are prevailing in this cropping system,which leads to a series of problems such as low fertilizer utilization efficiency and nutrient leaching losses.Hence,reasonable water and nutrient management is key to improve resource use efficiency and protect environment.In order to investigate the effects of water and nutrient optimization and biochar application on crop yield,N and P utilization efficiency and leaching loss under winter wheat/summer maize cropping in Guanzhong Plain.A 4-year field lysimeter experiment was performed on Lou soil（loess-derived and developed on natural cinnamon soil）in Yangling,Shaanxi Province,Northwest China.Seven treatments were used to investigate crop yield,N and P use efficiency,and N and P leaching:conventional practices（CP1,lysimeter depth=120/150 cm;CP2,lysimeter depth=100 cm）,CP1 plus reduced water supply（CP1-W）,CP1 plus reduced nutrient supply（CP1-F）,CP1 plus reduced water and nutrient supplies（OPT）,CP2 plus biochar application（CP2+B）,and OPT plus biochar application（OPT+B）.The main results and conclusions are as follows:1)During the four years,winter wheat and summer maize grain yield varied from 3099 to6954 kg ha^-1 and 6779 to 15732 kg ha^-1 respectively.Compared with CP1,CP1-W had no significant effects on wheat and maize grain yield;CP1-F significantly reduced wheat yield in seasons of 2017-2018,2019-2020（10.4%and 16.2%）,but had no significant effects on summer maize and annual crop yield.Compared with CP1,except for 2017-2018,OPT significantly reduced the total crop yield in the other three rotation years.Compared with CP2,CP2+B significantly increased total crop yields by 16.5%on average in rotation years except2018-2019,while OPT+B significantly reduced total crop yields in 2018-2019 and 2019-2020by 15.2%on average（compared with OPT）.2)Compared with CP1,CP1-W had no significant effects nitrogen partial factor productivity（PFP_N）,phosphorus partial factor productivity（PFP_P）,nitrogen utilization efficiency（NUE）and phosphorus utilization efficiency（PUE）（balance method）,but CP1-F significantly improve PFP_N and PFP_P,improve NUE and PUE（2016-2017,2018-2019）,including PFP_N and PFP_P four years on average increased 32.2%and 67.0%respectively.Compared with CP1,OPT significantly increased PFP_N by 26.4%on average（except 2016-2017）,and PFP_P increased by 56.2%four years on average.Compared with CP2,CP2+B significantly increased PFP_N by 17.8%on average（2017-2018,2018-2019）and four rotations PFP_P（39.9%）and PUE by 53.9%on average（balance method）.Compared with OPT,OPT+B significantly reduced PFP_N（2018-2019,2019-2020）,and significantly increased the 2018-2019 PFP_P（14.6%）.In general,application of biochar had no significant effects on NUE and PUE（balance method）.3)The main form of the nitrogen leaching loss was organic nitrogen（ON）,followed by nitrate nitrogen（NO₃^--N）,and ammonium nitrogen（NH₄⁺-N）was the lowest in the four rotation years.Compared with CP1,CP1-W had no significant effects on total nitrogen（TN）leaching,but OPT significantly reduced TN and NO₃^--N leaching.In addition to 2018-2019,Compared with CP2,CP2+B significantly reduced the average annual NO₃^--N,ON and TN leaching loss by 50.5%,31.5%and 36.0%,respectively,while Compared with OPT,OPT+B significantly reduced TN and ON leaching loss（2016-2017,2017-2018）,but significantly increased TN and ON leaching losses（2018-2019,2019-2020）.4)The main form of the P leaching losses was molybdate-reaction phosphorus（MRP）in four rotation years.Compared with CP1,CP1-W and CP1-F decreased total phosphorus（TP）leaching losses（except 2016-2017）,OPT significantly decreased particulate phosphorus（PP）,soluble organic phosphorus（DOP）and TP leaching losses（2018-2019）.Compared with CP2,CP2+B had no significant effects on P leaching losses,while compared with OPT,OPT+B significantly increased the TP leaching losses（2017-2018,2018-2019）.In conclusion,CP1-W can maintain crop yield.CP1-F and OPT can significantly improve PFP_N and PFP_P,improve NUE and PUE in some rotation years,and reduce leaching loss of N and P.However,long-term water and nutrient simultaneous optimization can significantly reduce the total crop yield in rotation years.CP1-F could increase the total crop yield,PFP_Nand PFP_P,and PUE,and reduce N leaching loss.However,OPT could reduce crop yield and PFP_N and PFP_P,and increase the risk of leaching of N and P.Therefore,under different water and fertilizer conditions,the effects of biochar application on crop yield,NUE and PUE and N and P leaching losses are not consistent,which needs further study.