Reduced tillage with residue retention and nitrogen application rate increase N2O fluxes from irrigated wheat in a subtropical floodplain soil

Abstract

Nitrous oxide (N2O) emissions were measured in irrigated wheat (Triticum aestivum) in an annual wheat- mungbean (Vigna radiata)-rice (Oryza sativa L) rotation that had been running for seven consecutive years. Effect of two soil disturbance levels (strip vs. conventional tillage; ST vs. CT both with 30 % residue retention) and three nitrogen (N) fertilizer rates (60, 100 and 140 % of the recommended N fertilizer dose, RD; called hereafter 60RD, 100RD and 140RD, respectively) were assessed. Mean N2O fluxes were about 110 % higher in ST than in CT. The rate of N fertilizer application influenced the mean and cumulative N2O fluxes with significantly higher fluxes in ST than in CT. Based on the respective maximum grain yields (CT: 140RD, 3.52 t ha−1; ST: 60RD, 3.19 t ha−1) yield-scaled N2O emissions were higher in ST than those in CT. However, tillage vs. N rate interactions showed both the highest and lowest yield-scaled N2O fluxes in ST with 140RD and 60RD, respectively. Soil microbial biomass carbon (MBC), organic carbon (SOC), total N (TN), nitrate (NO3- -N), aggregate mean weight diameter (MWD) and larger aggregate size classes (2.0‒0.85 and >2.0 mm) were significantly higher in ST and positively correlated with N2O fluxes. Our results highlight that, despite increased N2O emissions, ST with residue can trade-off emissions to improve soil macro aggregation, C sequestration and retention of N and crop yield with the lower N fertilizer and other energy inputs. Reduction of the recommended N fertilization rate could be considered if ST is adopted.