Crop residue incorporation and nitrogen fertilizer effects on greenhouse gas emissions from a subtropical rice system in Southwest China

Crop residue incorporation has been widely accepted as a way to increase soil carbon(C) sequestration and sustain soil fertility in agroecosystems. However, effect of crop residue incorporation on greenhouse gas(GHG) emissions in rice paddy soils remains uncertain. A field experiment was conducted to quantify emissions of CH4and N2O and soil heterotrophic respiration(RH) from a paddy rice field under five different crop residue treatments(i.e., 150 kg N ha-1of synthetic N fertilizer application only [NF], 150kg N ha-1of synthetic N fertilizer plus 5.3 Mg ha-1wheat residue [NF-WR1], 150 kg N ha-1of synthetic N fertilizer plus 10.6 Mg ha-1wheat residue [NF-WR2], 75 kg N ha-1of synthetic N fertilizer plus 10.6 Mg ha-1wheat residue [50%NF-WR2] and 150 kg N ha-1of synthetic N fertilizer plus 21.2 Mg ha-1wheat residue [NF-WR3]) in southwest China. Our results showed that crop residue incorporation treatments(NF-WR1, NF-WR2, 50%NF-WR2, NF-WR3) significantly increased CH4emissions by at least 60%, but N2O emissions were not enhanced and even suppressed by 25% in the NF-WR3 treatment as compared to the NF treatment. Soil RH emissions were comparable among experimental treatments, while crop residue incorporation treatments significantly increased soil carbon sequestrations relative to the NF treatment. Overall, CH4emissions dominated total global warming potentials(GWP) across all experimental treatments. The average yieldscaled GWPs for the NF and NF-WR1 treatments were significantly lower than for the NF-WR2, 50%NFWR2 and NF-WR3 treatments. Given the comparable yield-scaled GWPs between the NF and NF-WR1 treatments, the NF-WR1 treatment could gain net carbon sequestration as compared with the NF treatment with net soil carbon loss. Our findings suggest that the NF-WR1 treatment should be an effective option to sustain rice production while mitigating GHG emissions from the rice field in China.