Nitrous oxide and nitrate as indicators of subsoil removal of N in pig slurry applied to Luvisols in Western Denmark

Abstract

This one-year study examined effects of autumn- vs. spring- application of pig slurry, and the effect of a nitrification inhibitor (DMPP) for autumn-applied slurry, on transport and transformations of nitrogen in the soil profile. Duplicate field plots had ceramic suction cells at 50, 100, and 150 cm depths to calculate leaching for each treatment using NO3− concentrations and percolation simulated using a water transport model. Furthermore, soil moisture, soil texture and bulk density at 50, 100 and 150 cm depth, and water table level, were recorded. During campaigns, subsurface N2O concentrations at 20, 50, 100, and 150 cm depths, and N2O fluxes to the atmosphere, were monitored for indicators of denitrification activity. Autumn-applied pig slurry showed evidence for NO3− removal between 50 and 100 cm depth, and N2O concentration profiles indicated high denitrification activity around 50 cm depth. Autumn-applied slurry showed higher N2O emissions and lower crop yields compared to spring application, indicating losses occurred during winter. DMPP did not reduce average NO3− leaching, nor affect N2O emissions, but treatment effects were confounded by heterogeneity in compaction, clay content, and water table depth at plot level. The study showed that accounting for transport and transformations of N in the subsoil can contribute to understanding the environmental controls of N leaching, as well as direct and indirect N2O emissions.