Dynamics of Soil CH4 and CO2 Fluxes from Cattle Urine with and Without a Nitrification Inhibitor, and Dung Deposited onto a UK Grassland Soil

Food production systems associated with livestock management are significant sources of greenhouse gases (GHGs). Livestock excreta are one of the primary sources of GHG emissions from grazing livestock. Against this context, a field experiment was established in a UK grassland to establish the extent of soil methane (CH4), carbon dioxide (CO2), andN2O fluxes upon the deposition of (i) cattle urine (U), (ii) urine + dicyandiamide (DCD) (U + DCD), (iii) artificial urine (AU), and dung (D), and compared with a (iv) control, where neither urine nor dung was applied. Excreta applications were made at three experimental periods during the grazing season: early-, mid-, and late-season. Soil N2O emissions data have been published already by co-authors; hence, this paper summarizes the emissions of soil-borne CH4 and CO2 emissions, and explores in particular, the effects of the addition of DCD, a nitrification inhibitor used to reduce direct and indirect N2O emissions from urine patches, on these (carbon) C-GHGs. Soil moisture (p = 0.47), soil temperature (p = 0.51), and nitrate (NO3−) (p = 0.049) and ammonium (NH4+) (p = 0.66) availability, and C (p = 0.54) addition were key controls of both soil CH4 and CO2 emissions. The dung treatment stimulated the production and subsequent emissions of soil CH4 and CO2, a significantly high net CH4 and CO2-based global warming potential (GWP). The findings of the current study lay a foundation for an in-depth understanding of the magnitude and dynamics of soil-borne CH4 and CO2 upon urine and dung deposition during three different seasons. This study implies that the use of DCD may have the potential to reduce carbon-based GHGs from the urine and dung of grazing animals.