Effects Of Straw Returning Mode On Soil Fertility In Rice-Wheat Rotation System

Straw is rich in carbon,nitrogen,phosphorus,potassium and other nutrients,micronutrient,is an important renewable organic resources.At present,the study on the effect of straw returning on soil fertility in rice-wheat rotation mostly focuses on the topsoil,but neglects the study of soil nutrients in soil profile.In addition,the balance between micronutrient and soil enzyme activities in straw returned soil was also less.In this study,using a location test,four full-scale returning patterns of wheat and rice straw to field（CK）,wheat straw to field（Wr）,wheat straw to field（Rw）,wheat straw to field and rice straw to field（RwWr）were set up,soil pH,EC,organic matter,major elements,micronutrient,soil enzyme activities,rice and wheat yields were measured at different growth stages in the plough layer and profile（0-100cm）,to study the effect of total straw return on soil fertility in rice-wheat rotation system,in order to provide scientific basis for rational.utilization of straw resources,regulation of soil nutrients and increase of crop yield.The main findings are as follows:1.The total amount of straw returned to the field had a significant effect on the soil nutrient content in the tilth layer（0-5cm,5-10cm,10-20cm）at different growth stages of rice and wheat.Straw incorporation decreased soil pH,increased soil organic matter,available nitrogen,available potassium and available phosphorus,and increased the most in RwWr treatment.The soil pH value increased with the depth of soil layer,and the content of soil organic matter,available nitrogen,available potassium and available phosphorus decreased with the depth of soil layer.During the four growth stages of rice and wheat,the pH value of soil decreased firstly and then increased,the lowest at heading stage and the highest at maturity stage,which was consistent with the trend of soil available potassium content.There was no significant change in the content of alkali-hydrolyzable nitrogen.2.The results of soil analysis of 0-100cm rice-wheat profile showed that the soil pH was lower in the treatment of returning straw to field than that in the control The contents of soil organic matter,available phosphorus,available potassium,alkali-hydrolyzed nitrogen,water-soluble calcium and magnesium,available iron,manganese,copper and zinc were increased Soil organic matter,alkali-hydrolyzable nitrogen,ammonium nitrogen,nitrate nitrogen and available potassium decreased with the increase of soil depth,and the content of available phosphorus first increased and then decreased.For paddy soils,the soil pH increased with the depth of soil layer,and the contents of available Fe,Mn,Cu and Zn decreased with the depth of soil layer For wheat soil,the soil pH decreased with the increase of soil depth,and the content of available Fe,Mn,Cu and Zn increased first and then decreased.RwWr was the best way to improve soil nutrients.3.Compared with CK,the activities of soil neutral phosphatase,urease,sucrase and Catalase were increased in all treatments,the increases were 17.76%-28.57%,11.90%-15.53%,9.94%-19.72%and 1.69%-12.69%respectively.The activity of soil neutral phosphatase was RwWr>Wr>Rw>CK.Soil urease,sucrase and Catalase showed RwWr>Rw>Wr>CK.RwWr treatment,that is,returning straw to field in two seasons,increased the most among the four soil enzyme activities,and there were significant differences between RwWr and CK（p<0.05）.4.Compared with CK,the yield of rice and wheat increased by 7.96%-12.54%and 2.06%-10.01%respectively.The total spikelets,panicle number per panicle and grain number per panicle increased after straw returning treatment,and RwWr treatment increased the most.From the analysis of yield components of wheat,the grain number per spike and 1000-grain weight of wheat were increased by returning straw to field,among which RwWr increased the most,the increase of panicles per unit area in Wr treatment was significantly higher than that in Rw and RwWr treatment.In conclusion,the total straw return model can not only improve soil nutrient content and soil enzyme activity,but also have a positive effect on nutrient accumulation in the middle and lower soil layers of rice-wheat rotation system,the results showed that Wr treatment had the most significant effect on increasing wheat yield,but there was no significant difference compared with RwWr treatment,and RwWr treatment had the most significant effect on increasing rice yield,the difference was significant with Wr treatment.Therefore,in order to improve soil fertility and achieve sustainable,high-yield and high-efficiency crop production,RwWr treatment was suggested in rice-wheat rotation system.