Impacts Of Straw Returning Combined With Straw-decomposing Microbial Inoculant On Soil Carbon,Nitrogen,Phosphorus,and Potassium Contents In China’s Farmland

Soil carbon（C）,nitrogen（N）,phosphorus（P）and potassium（K）play an important role in farmland and other ecosystems.Straw returning is an important measure to improve soil quality and straw resource utilization,but straw returning alone is facing slow decomposition problem,which limits its popularization and application.This problem can be solved by applying straw decomposing microbial inoculants（SDMI）.At present,a series of studies use SDMI to promote the efficient utilization of straw resources.However,the field application effect of single experiment of SDMI is still controversial.Therefore,it is necessary to conduct a comprehensive and systematic study on the effects of straw returning with SDMI on soil C,N,P and K.This study conducted a meta-analysis to clarify the overall effect of straw returning combined with SDMI on soil C,N,P and K in China’s farmland,identify the relative importance factors of the effects for each environmental conditions and agricultural management practices,and summarized the best application scheme of SDMI to improve soil fertility.The field experiment was carried out to investigate best application scheme of SDMI.In order to clarify the field application effect of straw returning combined with different SDMI on soil C,N,P and K under the best application scheme of SDMI.The main research results were as follows:1、The results of meta-analysis showed that straw returning combined with SDMI could significantly improve soil organic carbon（SOC）content（95%CI,1.98～2.60）compared with straw returning（P<0.05）.The effects was relatively stable under different environmental conditions and agricultural practices,there was significant difference between different factors in the same group.Soil p H,mean annual precipitation（MAP）,soil organic matter content（SOM）and mean annual temperature（MAT）were relative importance factors of its effect.The field experiment showed that compared with control SF,straw returning with SDMI treatment SFD1,SFD2 and SFD3 could increase the SOC content by 11.69%,12.14%and 2.90%,respectively.The treatment SFD1 and SFD2 could significantly increase the active organic C by 18.85%and 17.99%,respectively（P<0.05）.2、The results of meta-analysis showed that straw returning combined with SDMI could significantly improve the soil total N（95%CI,1.39～1.95）and available N contents（95%CI,1.10～1.86）compared with straw returning（P<0.05）.This effects was relatively stable under different environmental conditions and agricultural management.The MAT,straw returning conditions（RC）,straw returning methods（SRM）,SOM,straw returning amount（SRA）and soil p H were relative importance factors of its effect.For soil available N,the different SRM,SRA and SDMI amount will change the effect of SDMI on available N.MAT was relative importance factors of its effect.The field experiment showed that compared with SF,the SFD2 could increase the total N content by 4.42%.The SFD1 and SFD2 could significantly increase 14.28%and 15.64%available N（P<0.05）.3、The results of meta-analysis showed that the soil total P（95%CI,1.87～3.28）and available P content（95%CI,0.81～1.22）could be significantly increased by straw returning with SDMI compared with straw returning（P<0.05）.Different climate regions,SOM content,soil p H,RC,SDMI amount and returning years could change this effects on total P.Soil p H,MAP and SRA was most important predictors of its effects.For soil available P,only when the SDMI amount>30 kg·hm^-2,its effect was insignificant.The MAT,MAP and RC was important predictors of its effect.The results of field experiment showed that SFD1,SFD2 and SFD3 increased the soil total P by 9.09%,9.09%and 2.27%and increased available P by 29.02%,26.34%and 6.25%compared with SF,respectively.4、The results of meta-analysis showed that straw returning combined with SDMI could significantly increase soil total K（95%CI,0.27～0.90）and available K content（95%CI,1.28～1.77）compared with straw returning（P<0.05）.Different climatic regions,soil p H,RC,SRM,SRA,initial C/N,SDMI amount and returning years could change this effect on total K,but there was no relative importance factors.For soil available K,this effects was stable under different environmental conditions and agricultural management measures.The SDMI amount and soil p H were important predictors of its effect.The results of field experiment showed that SFD1,SFD2 and SFD3 treatments increased total K by 1.92%,3.37%and 2.88%,the SFD2 increased available K by 4.49%compared with SF.In summary,the effect of SDMI on SOC was significantly higher than that of N,P and K.There was no significant difference between different form N.The effects of total P and available K were significantly higher than available P and total K,but SDMI application significantly increased soil C,N,P and K content.Under the subtropical monsoon climate and initial C/N>25,the SRA≤6000 kg·hm^-2straw and the SDMI amount≤30 kg·hm^-2ploughed into neutral soil with,will have the greatest effect on improving soil C,N,P and K.Therefore,SDMI application is a good way to promote straw decomposition,improve soil fertility,achieve green development and sustainable utilization of straw.