Wet-dry cycles control the emissions and sources of greenhouse gases in agricultural soil: An incubation study.

This study examines the impact of wet-drying cycles and nitrogen (N) fertilization on soil greenhouse gas fluxes, specifically nitrous oxide (N2O) and carbon dioxide (CO2). Nine treatments were tested, combining three soil moisture regimes (55% constant, 55%-30% cycle, and 80%-55% cycle) with three N addition rates (0, 100, and 150 kg N ha-1) using 15N-labeled urea. Soil samples from a potato (Solanum tuberosum) field in Lethbridge, Alberta, were incubated for 28 days under controlled conditions. Wet-drying cycles involved initially wetting the soil to the upper threshold (55% or 80% WFPS) and allowing it to dry to the lower threshold (30% or 55% WFPS), followed by rewetting to restore upper moisture levels. N2O and CO2 fluxes were measured regularly using a recirculation chamber system to quantify gas emissions and determine N2O sources. Soil moisture significantly increased N2O and CO2 production (p < 0.001), with the highest emissions under wet conditions (80%-55% WFPS cycle), moderate production at 55% WFPS, and the lowest under dry conditions (30%-55% WFPS cycle). Compared to constant 55% WFPS, N2O and CO2 production were 33% and 403% higher, respectively, under wet conditions and 28% and 3% lower under dry conditions. Rewetting events triggered temporary increases in gas emissions due to enhanced microbial activity. Urea addition caused a stronger priming effect on N2O production under wet conditions, with urea-derived N2O more prominent in wetter soils.