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 CH₄ and N₂O and soil heterotrophic respiration (R_H) from a paddy rice field under five different crop residue treatments (i.e., 150 kg N ha^-1 of synthetic N fertilizer application only NF], 150 kg N ha^-1 of synthetic N fertilizer plus 5.3 Mg ha^-1 wheat residue NF-WR1], 150 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue NF-WR2], 75 kg N ha^-1 of synthetic N fertilizer plus 10.6 Mg ha^-1 wheat residue 50%NF-WR2] and 150 kg N ha^-1 of synthetic N fertilizer plus 21.2 Mg ha^-1 wheat 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 CH₄ emissions 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 R_H emissions were comparable among experimental treatments, while crop residue incorporation treatments significantly increased soil carbon sequestrations relative to the NF treatment. Overall, CH₄ emissions 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.