Emissions of CH4 and CO2 from paddy fields as affected by tillage practices and crop residues in central China

A field experiment was conducted to investigate effects of tillage practices [no-tillage (NT) and conventional intensive tillage (CT)] and oilseed rape residue returning levels (0, 3000, 6000, 9000 kg dry matter ha(-1)) on methane (CH4) and carbon dioxide (CO2) emissions and grain yield from paddy fields during the 2011 rice growing season after 2 years oilseed rape-rice rotation in central China. The experiment was established following a split-plot design of a randomized complete block with tillage practices as the main plots and residue returning levels as the sub-plots. NT significantly decreased CO2 and CH4 emissions by 38.8 and 27.3 % compared with CT, respectively. Residue returning treatments released significantly more CO2 and CH4 by 855.5-10410 and 51.5-210.5 kg ha(-1) than no residue treatments, respectively. The treatments of 3,000 and 6,000 kg ha(-1) residue returning significantly increased rice grain yield by 37.9 and 32.0 % compared with the treatment of no residue returning, respectively. Compared with NT, CT increased yield-scaled emissions of CH4 and CO2 by 16.0 %. The treatments of 6,000 and 9,000 kg ha(-1) residue returning significantly increased yield-scaled emissions of CH4 and CO2 by 18.1 and 61.5 %, respectively, compared with the treatment of no residue returning. Moreover, the treatment of NT in combination with 3,000 kg ha(-1) residues had the lowest yield-scaled emissions of CH4 and CO2 across tillage and residue treatments. In this way, this study revealed that the combination of NT with 3,000 kg ha(-1) residues was a suitable strategy for optimizing carbon emissions and rice grain yield.