Tillage and crop residue management significantly affects N-trace gas emissions during the non-rice season of a subtropical rice-wheat rotation

Field operations of tillage and residue incorporation could have potentially important influences on N-trace gas fluxes, though poorly quantified. Here we studied the effects of straw incorporation in the preceding rice season and no-tillage prior to wheat sowing on nitric oxide (NO) and nitrous oxide (N2O) emissions during the non-rice period of a typical rice-wheat rotation in the Yangtze River Delta. Compared to conventional management practice (no straw incorporation along with rotary harrowing tillage to 10 cm before wheat sowing), straw incorporation alone decreased cumulative N2O emissions over the entire non-rice period by 32% (1.53 vs. 2.24 kg N ha-1, P < 0.05) but did not affect NO emissions (0.88 vs. 0.87 kg N ha−1). In contrast, no-tillage alone increased N2O emissions by 75% (P < 0.05) while reducing NO emissions by 48% (P < 0.01). Combination of no-tillage and straw incorporation led to no change in N2O emissions but a reduction in NO emissions compared to the conventional management regime. The direct N2O emission factors (EFds) of applied nitrogen fertilizers during the non-rice season ranged from 0.29% to 1.35% with a coefficient of variation (CV) as large as 68% among the investigated management regimes. The EFds for NO ranged from 0.13% to 0.32% with a CV of 50%. Adoption of these new EFds will allow us to account for management effects on N-trace gas emissions when calculating emission inventories. Nevertheless, it is noteworthy that the uncertainty remains high, since the effects of soil properties such as texture or pH on management practices are not yet well defined.