Effects And Potential Of Conservation Tillage On Soil Carbon Sequestration And Greenhouse Gases Emission Reduction In China Based On Meta-analysis

Due to the benefits of controlling soil erosion,maintaining soil water and fertility,saving time and labor,conservation tillage?CT?has been adopted globally.Facing the changing climate,CT is regarded as a key strategy to adapt and mitigate climate change.However,controversial results on soil organic carbon?SOC?,greenhouse gases?GHGs?emissions,and crop yields under CT exit widely among previous studies.Thus,an integrated assessment of CT effects on SOC sequestration,GHGs emissions,and crop production is critical to CT extension in China.Based on more than 200 literatures published before 2016,a national meta-analysis was conducted to assess the effects and main influential factors of no-till with residue removed?NTO?and no-till with residue retention?NTR?on SOC concentration and stock,GHGs?CH4 and N2O?emissions,and crop yields compared to plow tillage with residue removed?PTO?or plow tillage with residue retained?PTR?.The potential of NTR on SOC sequestration and crop production in China were computed on the basis of the results of meta-analysis.Main findings are as following:?1?Compared to PTO,SOC concentration was observed significantly increased by 5.5%and 8.2%under NTO and NTR in the national scale,respectively?P<0.05?;SOC stock was increased by 4.0%and 8.0%under NTO and NTR,respectively?P<0.05?.These results indicated combined with residue retention,the effects of NTR on SOC sequestration could be enhanced.However,the significant increases in SOC concentration and stock under NTR were limited in 0^-10 cm soil depth.Additionally,increasing in soil pH,avoiding excess soil wetness and temperature,long-term implementation could benefit the effects of NTR on SOC sequestration.?2?A significant decrease by 30.0%of CH4 emission was observed in rice-paddies under NTO compared to PTO?P<0.05?.However,N2O emission was significantly increased by 82.1%,25.5%,and 20.8%in rice-paddies,acid soils,and first 5 years of adoption under NTR compared to PTO,respectively?P<0.05?.The increase in N2O emission partly offset the benefits of low CH4 emission on climate change mitigation.In upland soils,a trend of enhancing CH4 uptake was observed under NTO and reducing N2O emission was observed under NTR,respectively.Results also indicated optimal nitrogen fertilizer input,avoiding excess soil wetness,and long-term implementation can enhance the mitigation of GHG emissions from China's croplands under NTR.?3?Generally,the decline in crop yield under NTO could be alleviated when combined with residue retention under NTR.The results present herein indicated NTR significantly increased crop yield by 4.6%compared to PTO?P<0.05?.After 10 years of implementation,a significant increase by 21.3%was observed under NTR compared to PTO?P<0.05?.Furthermore,the improvement in soil quality?increases in SOC concentration,soil water storage at harvest,soil available nitrogen,and available potassium content?was attributed to the increase in crop yield under NTR.In addition,among site-specific conditions,crop production under NTR for rice and wheat,at relative warm areas,very drought or very moist areas,weakly alkaline soils,with medium soil quality,or with appropriate nitrogen fertilizer input could be enhanced.?4?The national average SOC sequestration rate was 0.52 Mg C ha^-1 yr^-1 under NTR compared to PTO.At current situation,NTR could sequestrate SOC of 5.73 Tg C yr^-1 in China with a potential as high as 45.10 Tg C yr^-1.Combined with reduction on GHGs emissions,the total SOC sequestration under NTR was 5.91 Tg C yr^-1 at current scale with the highest potential of 48.93 Tg C yr^-1 after fully implement of NTR in China's croplands.Along with the benefits on carbon sequestration,total cereal production?wheat,rice,and maize?can be increased by 0.3?4.3%under NTR in China.