Effects Of Chinese Milk Vetch And Rice Straw Incorporation On Rice Growth And Soil Carbon Conversion

As an important renewable natural organic fertilizer source in China,the effect of Chinese milk vetch(MV)and rice straw in replacing chemical fertilizers and improving soil fertility to promote green agricultural production is one of the hotspots of current research.In the present study,we investigated the effects of the return of MV and rice straw alone and together on rice yield,nutrient uptake,soil fertility,soil active organic carbon fraction(dissolved organic carbon(DOC),hot-water extractable carbon(HWC),microbial biomass carbon(MBC),readily oxidizable carbon(ROC))and carbon invertase activity(sucrase,cellulase,β-glucosidase)under a 40% nitrogen fertilizer reduction using a field trial in MV-rice crop rotation.This study will further clarify the synergistic effects of MV and rice straw in reducing chemical fertilizers and improving soil fertility,with a view to providing a theoretical basis and technical support for green rice production.The main findings are as follows:(1)Compared with the full amount of nitrogen fertilizer alone(N100),both the treatments of MV alone(MV+N60)and the co-incorporation of MV and rice straw(MV+S+N60)at the reduced level of 40% nitrogen fertilizer could maintain rice yields.The average rice yields in three years were similar for the treatments of MV+N60 and MV+S+N60,with an increase of 13.1% and 11.4%,respectively,comparing with that of S+N60.(2)Both the return of MV and rice straw can improve the nutrient uptake and utilization by rice,and meanwhile improve soil physical and chemical properties and increase the content of total nitrogen,organic matter,available phosphorus and available potassium to a certain extent.Compared with the treatment of N100,the accumulation of nitrogen,phosphorus and potassium nutrients in rice grain increased by 17.9%,14.3% and4.4%,respectively,while the accumulation of nitrogen,phosphorus and potassium nutrients in rice straw increased by 45.3%,18.5% and 24.7%,respectively,for the treatment of MV+S+N60,which met the nutrient requirement of rice whilst maintaining soil nutrient supply capacity.(3)Combined return of MV and rice straw increased the content of soil total organic carbon and active organic carbon fractions.Compared with N100,the DOC,HWC,ROC and MBC contents of the MV+S+N60 treatment increased by 5.2%-17.1%,10.2%-40.1%,7.3%-17.6%,17.6%-25.8% and 0.4%-63.1%,respectively,which were higher than those of MV+N60 and S+N60 treatments.(4)Returning MV and rice straw to the field alone and together increased the activities of carbon invertase at rice transplanting and harvesting stages.Compared with N100,the treatments of MV+N60 and MV+S+N60 could improve soil sucrase,cellulose,and β-glucosidase activities and the β-glucosidase activity was significantly increased by 16.7%.The S+N60 treatment improved soil sucrase and cellulase activities.(5)There were significant correlations between active organic carbon fractions and the activities of carbon invertase.Cellulase activity showed a significantly positive correlation with DOC and HWC contents;β-glucosidase activity showed a significantly positive correlation with ROC and MBC contents.In summary,the co-incorporation of MV and rice straw can increase soil organic matter content,improve the activity of enzymes related to soil carbon conversion,accelerate soil organic matter activation,improve soil fertility characteristics,provide favorable environmental conditions for crop growth,increase fertilizer use efficiency,maintain rice yield,and support the green development of agriculture.