Mechanisms Of Chinese Milk Vetch And Rice Straw Incorporation In Affecting Greenhouse Gas Emissions From Paddy Soil

Extensive use of chemical fertilizers(CF)will increase greenhouse gas(GHG) emissions,exacerbating global warming and climate change.Therefore,it is necessary to adopt sustainable production techniques to mitigate the harmful effects of CF on soil and ecosystems.The input of organic resources can reduce the use of CF and supplement soil organic matter.Organic matter is an important soil carbon sink,and its mineralization process is closely related to GHG emissions and soil properties.In view of this,the present study aims to reduce GHG emissions and improve soil properties through the combination of organic and inorganic inputs.The main contents of this study include:(1)evaluating the effect of Chinese milk vetch(CMV)and rice straw(RS)incorporation on GHG emissions and soil properties with or without nitrogen(N)fertilizer addition;(2)studying the effectiveness of incorporating CMV and RS to partially replace N fertilizers and their effects on GHG emissions,as well as rice growth and productivity in a pot study;(3)determining the effect of short aerobic decomposition before flooding on reducing GHG emissions.The main results are summarized as follows:1.The co-incorporation of CMV and RS combined with N fertilizer can more effectively reduce CH4 emissions and improve soil fertility.Adding RS alone increased methane(CH4)emissions compared to CMV,while CMV was less effective in C sequestering,N immobilization,and maintaining dissolved organic C(DOC)and microbial biomass C(MBC)contents.Compared with RS,co-incorporation of CMV and RS reduced CH4 emissions,increased C sequestration,maintained a higher DOC content,reduced N loss,and maintained consistent and moderate levels of MBC and soil nutrients content.This balance may be related to the C/N ratio resulting from the co-incorporation of CMV and RS,which regulate the supply and demand of C and N and the associated biological processes.In addition,biomarkers measured by Biolog Eco Plate technology indicated that the combination of CMV,either alone or mixed with RS,was more effective in increasing the C sources utilization rate.2.The combined incorporation of CMV and RS can reduce the amount of N fertilizer,improve soil fertility,increase the absorption of nutrients by rice,improve the use efficiency of chemical fertilizers,and enhance the C sequestration rate without increasing the global warming potential in the rice growth period.The co-incorporation of CMV and RS and partial replacement of N fertilizers enhanced the growth and development of rice,the number of effective panicles,the nutrients(N,P,and K)content and accumulation in the rice biomass,and the ability to absorb nutrients from the soil.Green manure or RS incorporation increased CH4 emissions by increasing the abundance of the mcr A gene,the mcr A/pmo A ratio,and methanosarcina.The co-incorporation of CMV and RS with 60%of recommended N fertilizer(MSN60)had the highest rate of CH4 production,while carbon dioxide(CO2)was higher in MN60 compared to other treatments,and nitrous oxide(N2O)emission decreased due to residue incorporation.Overall,the combination of CMV and RS was more beneficial to soil C sequestration than the single incorporation of CMV or RS,and the changes in global warming potential were similar.The combined incorporation of CMV and RS residues improved soil fertility mainly by increasing the content of SOC,total N,available K,DOC,MBC,and the activity ofβ-glucosidase,cellulase,and sucrase enzymes compared to the incorporation of CMV or RS alone or the application of 100%of recommended N fertilizer.3.Co-incorporation of CMV and RS and short-term aerobic decomposition of crop residues before flooding significantly reduced GHG emissions.The short-term aerobic decomposition of organic materials returned to the paddy soil before flooding was very effective in reducing CH4 and CO2 emissions,with an average reduction of 16.5%-99.9%and6.6%-32.1%,respectively.The addition of RS to the soil also resulted in N immobilization,which enhanced the decrease of N2O emissions by 76.2%.The co-incorporation of CMV and RS was more effective in achieving this compared with CMV alone.The short aerobic decomposition had no effect on SOC and total N,but had a negative effect on dissolved organic C and NH4~+concentrations.In contrast,it enhanced the MBC and MBN contents.In summary,the results of this study concluded that the combined incorporation of CMV and RS reduced N fertilizer(40%of the recommended N fertilizer)use,improved soil fertility,increased nutrient uptake by rice,improved chemical fertilizer use efficiency,and increased the rate of C sequestration,which maintained balanced potential global warming rates compared to CMV or RS incorporation alone.Altogether,our findings suggest that the combined incorporation of CMV and RS with short-term aerobic decomposition prior to flooding can be an effective approach in reducing GHGs and improving soil fertility on a sustainable basis.