Effects Of Combined Application Of Different Ratios Of Straw And Chemical Fertilizers On Soil Carbon Pool,Soil Enzyme Activities And Wheat Yield Under Rice-Wheat Rotation System

Crop straw is rich in carbon,and returning it as an organic material can improve soil physical and chemical properties,maintain soil organic carbon content,and increase crop yields.Therefore,we study the effects of combined application of rice straw and chemical fertilizers on the stability of soil organic carbon,soil enzyme activities and winter wheat yield during the growth period of wheat under the conditions of paddy and dry rotation.This study can be applied to provide reference about evaluate the effects of straw on optimizing soil fertility and increasing crop yield.In this experiment,rice straw was used as the research object under field test conditions.The fertilizer levels（C）were 0%,70%,and100%,and the straw return levels（S）were 0%,50%,and 100%.There were 9 treatments.In this experiment,we tested the activities of soil sucrase（SUC）,urease（URE）,catalase（CAT）and acid phosphatase（ACP）during the period of wheat tillering stage,jointing stage and maturity stage,and analyzed the interactive effects of combined application of straw and chemical fertilizers on the activities of these four soil enzymes.We also analyzed the differences in soil microbial biomass carbon（MBC）,dissolved organic carbon（DOC）,particulate carbon（POC）,labile organic carbon（LOC）and mineralized carbon（MC）in different treatments during the period of maturity stage.At the same time,we studied the effects of combined application of straw and chemical fertilizers on wheat yield and its components.Finally,we analyzed the correlation between soil nutrient factors and soil organic carbon components,soil enzyme activities,and wheat yield.The main research results obtained are as follows:（1）Straw application,chemical fertilizer application and the combined application of both significantly increased the content of soil microbial biomass carbon,water-soluble carbon,particulate carbon,three types of active oxidizable carbon（LOC1,LOC2,LOC3）,and mineralized carbon.And the highest growth rates were 29.58%,17.85%,44.51%,28.72%,44.65%,73.15%,53.23%.Among them,MBC is the highest in S₅₀C₁₀₀,DOC is the highest in S₅₀C₀,POC is the highest in S₅₀C₇₀,and LOC1,LOC2,LOC3,and MC are the highest in S₁₀₀C₁₀₀.CPMI and the effectiveness of the three types of LOC are the highest in processing S₁₀₀C₁₀₀.In addition,the treatment of combined application of straw and chemical fertilizer has the best effect on soil microbial biomass carbon,particulate carbon,easily oxidizable carbon,the effectiveness of the three types of LOC,CPMI.Except for the insignificant correlation between DOC and the 3 types of LOC,there are significant or extremely significant positive correlations between the other organic carbon forms（P<0.05）.And there is a significant positive correlation between organic carbon and most of the soil nutrient factors（P<0.05）.（2）The combined application of straw and chemical fertilizers significantly increased the activities of soil invertase,urease,catalase and phosphatase,and showed a trend of increasing first and then decreasing with the increase of application amount.The increase of soil invertase and urease activity is mainly in the early and mid-term of wheat growth.The increase of soil catalase and phosphatase activity is mainly in the later stage of wheat growth.With the growth period of wheat,the soil enzyme activity changes regularly.The activities of invertase,urease,catalase and acid phosphatase are respectively changing between 0.06～0.17mg·g^-1,0.40～0.76mg·g^-1,4.06～10.38 ml·g^-1,9.28～16.09mg·kg^-1,and the four enzyme activities reach the highest stage in the treatment of S₅₀C₁₀₀.In addition,the combined application of straw and chemical fertilizers has obviously positive interactions on soil invertase,urease,catalase and phosphatase,and the effect of single application of straw on soil enzymes is better than that of single application of chemical fertilizer.Among the four soil enzymes,except for the significant positive correlation between urease and catalase,the other soil enzymes have extremely significant positive correlations.There are significant or extremely significant positive correlation between soil enzymes and soil nutrient factors（P<0.05）.（3）Combined application of straw and chemical fertilizers is beneficial to increase the yield of winter wheat,with the highest increase of 238.5%.Besides,the combined application of straw and chemical fertilizer is better than that of single application of chemical fertilizer or straw,and the treatment S₁₀₀C₁₀₀is the best.Combined application of straw and chemical fertilizers is also conducive to increase the wheat thousand-grain weight,spike length,plant height,grain number of per spike,spike number,and economic coefficient.The combined application of straw and chemical fertilizer is better than that of single application of chemical fertilizer or straw.Principal component analysis of wheat yield and other elements and soil nutrient factors showed that the treatment S₅₀C₁₀₀had the highest comprehensive score,and the combined application of straw and chemical fertilizer had the best effect.After correlation analysis,it is found that wheat yield and soil available nutrient content are positively correlated,and the trend of yield is same to the trend of nutrient.Single application of straw and single application of chemical fertilizer and their interaction have significant or extremely significant effects on soil nutrients,wheat yield and its components（P<0.05）.