Effects Of Continuous Straw Return On Soil Nutrients,Soil Microbial Activity And Carbon Pool In A Rice-wheat Rotation System

Nowadays,China is an agricultural country,which produces about 800 million t amount of crop straw every year and accounts for 30%in the world.Crop straw is also a kind of renewable material resource,including large quantities of carbon,nitrogen,potassium and phosphor,which could play an important role in improving soil fertility,and provide suitable environment for next crop.However,the less amount of straw return has little effect on soil fertility,but also results in nowhere to place crop residue.More amount of straw return will make the soil temperature and air exchange is not smooth,which is not conducive to crop growth.Therefore,it seems to be very important to study the effects of continuous straw return on soil fertility and crop growth.A three-year field experiment was conducted to determine the effects of different amounts of annual straw returning on soil nutrients,microbial activity,carbon pool and crop yields in a rice-wheat rotation system,seven treatments were applied with the gradient amount of 25%,50%,75%and 100%rice and wheat straw returning,100%amount of rice straw returning,100%amount of wheat straw returning,and no-straw returning acted as control.The aim is to explore a suitable amount of straw return for soil fertility and crop yield,it is significant to perfect the local straw counters-field technology and alleviate the pressure of the farmland ecosystem.The main conclusion were as follows:1.Effect of amount of continuous straw return on soil nutrients and crop yieldUnder this test fertilizer levels,after continuous five and six crops of straw return,all the straw return treatments increased soil available nitrogen,available potassium,available phosphorus,total nitrogen,total potassium and total phosphorus in a rice-wheat rotation system.We could conclude that,within the scope of this amount,straw return could improve soil fertility,and the treatment of continuous 75%amount of straw return had the most significant effect on soil nutrients.In this study,the treatment of continuous 75%and 100%amount of straw return had the most significant effect on yield of rice,which was increased by 12.88%and 13.30%,but the growth slowed after 75%amount of straw return,and the treatment of continuous 50%significantly increased wheat yields,which was increased by 14.29%,respectively.Nevertheless,100%both rice and wheat straw returning and 100%rice returning slightly decreased wheat yields.In addition,the trend of annual crop production was firstly increased and then decreased with the increasing amount of straw returning,with its peak of 10.01%improvement in the treatment of 75%.2.Effect of amount of continuous straw return on soil microbial activityIn wheat return on rice crop,the soil bacteria and actinomycetes were differently activated by 25%and 50%amount of straw return.In contrast,fungi were inhibited in varying degrees except in the treatment of 100%rice returning.In addition,100%both rice and wheat straw returning significantly increased the activity of catalase and unease in soil,while the activity of soil invertase was increased remarkably in the treatments of 25%and 75%.In rice return on wheat crop,the soil bacteria and actinomycetes were differently activated by 50%amount of straw return.which were increased by 14.85%and 24.58%.In contrast,fungi were inhibited in varying degrees except in the treatment of 75%rice returning.In addition,50%and 100%both rice and wheat straw returning significantly increased the activity of unease in soil,which were increased by 61.90%,while the activity of soil catalase and invertase were increased remarkably in the treatments of 50%and 75%.3.Effect of amount of continuous straw return on soil total organic carbon and labile organic carbonNo matter in rice and wheat crop,all the straw returning could increase the soil total organic carbon and labile organic carbon in the soil depths of 0-21 cm.With the increase in soil depth for all treaments,soil total organic carbon and easily oxidizable carbon contents generally decreased.The treatment of continuous 75%amount of straw return had the most significant effect in soil total organic carbon on rice crop,and the treatment of continuous 25%and 75%amount of straw return had the most significant effect in soil total organic carbon on wheat crop.In addition,50%and 75%five-season continuous returning significantly increased the contents of water-soluble organic carbon and easily oxidizable carbon in rice season,while continuous of 25%and 50%of both rice and wheat return in rice season,and 100%rice return significantly increased the contents of easily oxidizable carbon,25%and 75%amount of straw return significantly increased the contents of water-soluble organic carbon in wheat season.In summary,within the scope of this amount,straw return could increase soil total organic carbon and labile organic carbon,and the treatments of 25%to 75%amount of straw return had the obvious advantages than others.