Effect of wheat straw-biochar amendment on CO2 and N2O emissions from a Quaternary red soil

Due to the special properties of biochar (e.g., high carbon content, strong absorption, and high pyrolysis), soil biochar amendment is increasingly regarded as a new measure to sequester soil carbon and mitigate greenhouse gas (GHG) emissions. To investigate the effect and mechanism of biochar amendment on CO2 and N2O emissions from red soils, an incubation experiment was carried out with an upland soil developed from Quaternary red clay. Five biochar (derived from wheat straw) treatments was arranged, with the application rates at 0, 0.5%, 1%, 2% and 2.5% (w/w). No biochar treatment was the control treatment. The incubation lasted 60 d with a constant water content at field capacity in a culture room at 25 ℃. Significant correlations were observed between biochar application rates and CO2 and N2O emissions (P<0.01). During the 0-15 d incubation, especially in the first 2 d, CO2 emissions from the biochar amendment treatments were higher than the control treatment and increased with increasing biochar application rate, which might be caused by the decomposition of soluble organic and inorganic carbon within biochar. Contrary to CO2 emissions, biochar amendment reduced N2O emissions during first 10 d, in comparison with the control treatment. Due to its strong absorption capacity, biochar adsorbed and consequently reduced soil NH4 -N, and resultantly decreased N2O emissions via the nitrification process. Since Day 15, biochar amendments significantly reduced CO2 emissions by 8.2%-18.4% (P<0.05), compared to the control treatment. While, since Day 10, biochar amendments increased N2O emissions, compared to the control treatment. Over the entire incubation period of 60 days, biochar amendments increased CO2 (except for the biochar treatment with 0.5% rate reducing CO2 emission, P<0.05) and N2O emissions by -6.3%-18.7% and 16.9%-58.5% as compared to the control treatment, respectively. Our incubation experiment showed that the wheat straw-biochar amendments on a Quaternary red soil increased CO2 and N2O emissions, implying that biochar being a potential measure to mitigate greenhouse gas emissions from agricultural lands is controversial.