Nitrous oxide and methane fluxes from a rice–wheat crop rotation under wheat residue incorporation and no-tillage practices

Abstract

Crop residue incorporation and no-tillage are recommended as management practices and are being increasingly adopted in the agricultural sector. However, few studies have assessed the extent to which these practices integrate annual carbon and nitrogen trace gas fluxes and grain yield. We investigated the effect of wheat straw incorporation and no-tillage on nitrous oxide (N2O) and methane (CH4) fluxes from a rice–wheat system in southeast China, using year-round field measurements. Compared to the treatment with synthetic nitrogen fertilizers alone, the wheat straw incorporation reduced the N2O emissions by 38% (P < 0.05) and increased the CH4 emissions by 74% (P < 0.05) during the annual rotation cycle. Compared to the conventional tillage, no-tillage prior to wheat sowing enhanced the N2O emissions by an average of 61% (P < 0.05), irrespective of residue incorporation. The CH4-C emissions that were induced by the wheat straw comprised 6% of the residue-carbon incorporated during the rice season. As a result of the stimulating effect of wheat straw incorporation on CH4 fluxes, the annual aggregate emissions of N2O and CH4 with straw incorporation (10.7 Mg CO2-eq ha−1 yr−1 or 725 kg CO2-eq Mg−1 grain yield) were usually higher than those with no residue incorporation (7.6 Mg CO2-eq ha−1 yr−1 or 545 kg CO2-eq Mg−1 grain yield), irrespective of the tillage practice. Nevertheless, the changes in greenhouse gas emissions are notably only the transient response of the rice–wheat system after crop residue incorporation and tillage conversion, which may not necessarily represent equilibrium conditions for this agro-ecosystem over the long term.