Winter-Season Gaseous Nitrogen Emissions in Subtropical Climate: Impacts of Pig Slurry Injection and Nitrification Inhibitor

Controlling nitrogen (N) losses from pig slurry (PS) is a challenge under no-till because amendments are left on the soil surface. We investigated the potential of shallow injection of PS, with and without addition of the nitrification inhibitor dicyandiamide (DCD), to abate gaseous ammonia (NH₃) and nitrous oxide (N₂O) emissions in winter crops in subtropical soils. Injection was compared with surface broadcasting of PS, with and without DCD. The significance of winter season on annual N₂O emissions was assessed. Injecting PS reduced NH₃ volatilization compared with surface application. However, this reduction was partly offset because N₂O emissions increased by 77% (+1.53 kg N₂O-N ha⁻¹) when PS was injected. Adding DCD to injected PS reduced N₂O emission below levels of surface-broadcast PS without the inhibitor, indicating that DCD may be a management option when injecting PS. Compared with a reference urea treatment, PS without DCD increased cumulative N₂O emissions 5.7-fold (from 613 to 3515 g N₂O-N ha⁻¹) when injected, and 3.2-fold (from 613 to 1980 g N₂O-N ha⁻¹) when surface applied. Adding DCD significantly reduced emissions with injected PS, whereas reduction was not always significant with surface-applied PS. Nitrous oxide emissions during the winter cropping season contributed 30 to 44% of annual emissions, indicating that controlling gaseous N losses in that season is required to reduce the environmental footprint of the whole cropping system. Overall, combining PS injection with DCD was an efficient practice for reducing winter-season gaseous N losses from no-till soils under subtropical climate.