Reduced soil disturbance: Positive effects on greenhouse gas efflux and soil N losses in winter wheat systems of the southern plains

Soils produce greenhouse gases (GHG) from carbon (C) and nitrogen (N) mineralization. The GHGs of interest in cropped soils are carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Greenhouse gases of cropped soils in response to management disturbance in the Southern Plains of the United States after tillage have not been monitored and reported to date in the literature. It was hypothesized that undisturbed no-tillage treatment would produce less CO2, CH4, and N2O emissions compared to conventional tillage due to a flush of labile N and aeration of soil immediately after tillage. Methane emissions were hypothesized to increase following tillage due to disturbance. This study was conducted at the United States Department of Agriculture, Agricultural Research Service, Grazinglands Research Laboratory at El Reno, OK on 21-28 July 2015 and 25 July-August 1, 2016, post-harvest. Efflux rates of GHGs were monitored using stationary chambers and soil nitrogen, carbon and water were monitored before tillage, 0, 3, 6, 9, 24, 48, 96, 168 and 336 h after tillage in conventional (CT) and no-fill (NT) management systems. Soil water content was lower in CT than NT in both years. Tilling the soil resulted in a doubling of CO2 and N2O efflux. Methane assimilation decreased by two fold post tillage compared to before tillage efflux. Soil nitrate and ammonium increased after tillage and remained elevated. This study confirmed that water-filled pore space (WFPS) was an important driver of CO2. Mechanical disturbance through tillage appeared to be the biggest driver of N2O efflux and produced a flush of soil N. However, soil N availability, as a result of tillage, caused a transition of assimilation to efflux for CH4 that was not affected by WFPS.