Effects Of Returning Straw And Its Carbonized Form To Paddy Soil On Soil Organic Carbon And Enzyme Activit

Straw and its return to the field after carbonization can significantly affect the content,composition and mineralization of soil organic carbon,thus indirectly affecting the nutrient cycle,water Thermal equilibrium,turnover of Soil organic matter and greenhouse gas emissions of the soil in the agricultural ecosystem.Its application in farmland is conducive to carbon sequestration and emission reduction of paddy fields.Four treatments were set up in this study:no fertilizer（CK）,only fertilizer（NPK）,straw combined with fertilizer（NPKS）and Biochar combined with fertilizer（NPKB）.The response of soil organic carbon and its components,mineralization and enzyme activity to rice straw and its return to the field after carbonization was studied by field experiments and indoor mineralization culture.The main results are as follows:（1）Compared with NPKS treatment,NPKB treatment reduced the total organic carbon（SOC）content in paddy soil by 4.80%during the jointing stage,and increased it by 7.68%and 6.72%during the heading and ripening stages,respectively.From the perspective of the entire growth period,NPKB treatment showed the best improvement effect.The content of easily oxidizable organic carbon（ROC）,microbial biomass carbon（MBC）,and soluble organic carbon（DOC）and their ratio to SOC（ROC/SOC,MBC/SOC,and DOC/SOC）in different growth stages were highest in the NPKS treatment,which increased by 9.46%to 38.07%,4.01%to27.38%,17.30%to 27.39%,16.74%to 34.12%,1.39%to 35.81%,and 21.32%to36.74%compared to the NPKB treatment,respectively.（2）There was no significant difference in soil humic acid carbon（HAC）and fulvic acid carbon（FAC）content between NPKB treatment and NPKS treatment during different growth stages;The HMC content decreased by 5.95%during the jointing stage,and increased by 12.49%and 7.83%during the heading and ripening stages,respectively.The contribution of humification to soil total organic carbon by humic acid carbon is the greatest,and the degree of humification in each treatment decreases with the extension of growth period.The humification degree in NPKS and NPKB treatments is gradually increasing compared to CK and NPK treatments.（3）The mineralization rate of soil organic carbon shows a decreasing trend with cultivation time.From the 1st to 3rd day of cultivation,the mineralization rate of organic carbon sharply decreases,and from the 3rd to 45th day,it slowly decreases.Compared with NPKS treatment,the cumulative mineralization amount（C_t）and cumulative mineralization rate（C_t/SOC）of soil organic carbon in NPKB treatment at different growth stages decreased by 13.90%to 24.27%and increased by 9.57%to29.02%,respectively.NPKS treatment significantly increased the potential mineralizable organic carbon（C₀）content and C₀/SOC in soil,promoted soil organic carbon mineralization,and reduced soil organic carbon stability;NPKB treatment increased the turnover time of soil organic carbon,inhibited soil organic carbon mineralization,and enhanced soil organic carbon stability.（4）The activities of soil Catalase,Acid phosphatase,urease and Sucrase in each growth period were determined by The NPKS treatment was the highest,with an increase of 24.84%～49.54%,18.70%～45.26%,24.46%～63.81%,and 11.72%～67.57%compared to the NPKB treatment;And compared with CK and NPK treatments,NPKB treatment inhibited soil enzyme activity to varying degrees,especially during the mature stage.（5）Soil organic carbon mineralization index（C_t and C_t/SOC）was significantly positively correlated with soil active organic carbon,Catalase activity and Acid phosphatase activity（P<0.05）,and significantly negatively correlated with soil organic carbon and humin carbon（P<0.05）;Redundancy analysis（RDA）results show that easily oxidizable organic carbon（ROC）and microbial biomass carbon（MBC）are the main environmental factors affecting the distribution of organic carbon mineralization and enzyme activity in paddy soil.In summary,the application of straw combined with chemical fertilizers significantly increased the content of soil active organic carbon and soil enzyme activity,promoted the mineralization of soil organic carbon,and reduced the stability of soil organic carbon.Biochar combined with chemical fertilizer can significantly increase soil organic carbon content,increase soil humin carbon content and proportion,slow down soil organic carbon mineralization and inhibit soil enzyme activity,thereby enhancing the stability of soil organic carbon,promoting soil carbon sequestration and reducing carbon dioxide emissions.Straw carbonization returning to the field is a better way of returning to the field than directly returning straw.