A short-term study was conducted to investigate the greenhouse gas emissions in five typical soils under two crop residue management practices: raw rice straw (Oryza sativa L., cv) and its derived biochar application. Rice straw and its derived biochar (two biochars, produced at 350 and 500 degrees C and referred to as BC350 and BC500, respectively) were incubated with the soils at a 5% (weight/weight) rate and under 70% water holding capacity for 28 d. Incorporation of BC500 into soils reduced carbon dioxide (CO2) and nitrous oxide (N2O) emission in all five soils by 4-40% and 62-98%, respectively, compared to the untreated soils, whereas methane (CH4) emission was elevated by up to about 2 times. Contrary to the biochars, direct return of the straw to soil reduced CH4 emission by 22-69%, whereas CO2 increased by 4 to 34 times. For N2O emission, return of rice straw to soil reduced it by over 80% in two soils, while it increased by up to 14 times in other three soils. When all three greenhouse gases were normalized on the CO2 basis, the global warming potential in all treatments followed the order of straw > BC350 > control > BC500 in all five soils. The results indicated that turning rice straw into biochar followed by its incorporation into soil was an effective measure for reducing soil greenhouse gas emission, and the effectiveness increased with increasing biochar production temperature, whereas direct return of straw to soil enhanced soil greenhouse gas emissions.
