Meta analysis on impacts of biochar on trace greenhouse gases emissions from staple crops in China

Abstract: Biochar inputs have important impliations for agricultural soils, also have a significant influence on greenhouse gas emissions. This paper conducted a meta-analysis to quantitatively synthesize influence of biochar inputs on trace greenhouse gases from staple crops in China, and explored available mitigation method. The data were collected from published papers before December, 2016. The effective data were selected from the literatures including: 1) both treatments with and without biochar input; 2) methane and nitrous oxide emissions; 3) field experiment; 4) greenhouse gases from rice planting to maturity; 5) reliable measurements; 6) clear and reliable yield data; 7) wheat, rice and maize in China. A total of 134 datasets were obtained. They were classified by rice paddy field and dry land, rotary tillage and plowing tillage, different biochar amount and biochar types. The response ratio was calculated with the biochar input as the treatment and no biochar input as the control. The global warming potential and the greenhouse gas intensity were calculated. The results showed that the biochar input averagely decreased the global warming potential by 18% compared with no biochar input. The global warming potential decrease by inputting biochar in the dry land was significantly higher than that in the paddy field (P<0.01). The reduction in global warming potential by inputting less than 10 t/hm2 biochar was higher than that by inputting the biochar higher than 10 t/hm2. Plowing tillage could significantly reduce the GWP by 19%. The rate of change in GWP was highest in the other biochar (41%), followed by maize biochar (20%) and wheat biochar (13%). The biochar input didn't greatly affect the methane emission in paddy field. However, the rotary tillage could significantly increase the methane emission by 30% and the inputting biochar without N application also greatly increase the methane emission. The biochar input average decreased the nitric oxides by 41% for the three staple crops. The nitrous oxides emission was decreased by 44% in the dry land, 24% in the paddy field, by 52% by inputting smaller than 10 t/hm2 biochar. The nitrous oxides emissions were higher in the other biochar and maize biochar than the wheat biochar. Biochar input could increase the crop yield by 7% and decreased the greenhouse gas intensity by 25%. The decrease in the greenhouse gas intensity was higher in the dry land than the paddy field, in the smaller than 10 t/hm2 biochar input than the input higher than 10 t/hm2, and in the plowing tillage than in the rotary tillage. The rate of change in greenhouse gas intensity was 47% in the other biochar input, 26% in the maize biochar, and 20% in the wheat biochar. Different soil use types, tillage managements, biochar amount and biochar types could significantly impact nitric oxide, global warming potential and greenhouse gas intensity. In addtion, biochar input combined with reasonable agricultural management could reduce greenhouse gas emissions in staple crops soils. This paper indicated that for reduction in global warming potential from staple crops, biochar should combine application with nitrogen fertilizer and plowing tillage managements, and input the biochar with less 10 t/hm2 and C/N below 80, such as, field crop straw could directily carbonized.