Reducing Surface Wetting Proportion of Soils Irrigated by Subsurface Drip Irrigation Can Mitigate Soil N2O Emission.

To reveal the impact of soil moisture distributions on nitrous oxide (N2O) emissions from wet soils irrigated by sub-surface drip irrigation (SDI) with different surface soil wetting proportions, pot experiments were conducted, with surface irrigation (SI) as a control. Results indicated that irrigation triggered N2O pulsing effect in all SDI treatments, yet N2O values reduced with the decrease of surface soil wetting proportions of SDI irrigated soils, and the occurrence times were lagged. The peak N2O fluxes and the corresponding soil water filled pore space (WFPS), as well as the coefficients of determination (R²) of the exponential function between N2O fluxes and soil WFPS, decreased with the reduction of surface soil wetting proportions with SDI treatment, and from the central sub-region to the periphery sub-region. The pulse period contributed most to the reduction of N2O emissions in SDI compared to SI treatments and should be a key period for N2O emission mitigation. Over the whole experimental period, the area-weighted average cumulative N2O fluxes from SDI treatments were 82.3⁻157.3 mg N2O m-2 lower than those from SI treatment, with periphery sub-regions of R3 and R4 (radius of 19⁻27 cm and 28⁻36 cm from the emitter horizontally) contributing to more than 75.8% of the total N2O emission mitigation. These results suggest that reducing surface soil wetting proportions or the increments of topsoil WFPS for SDI irrigated soils is a promising strategy for N2O emission reduction.