Effects of dairy shed effluent dry matter content on ammonia and nitrous oxide emissions from a pasture soil

Abstract

Atmospheric emissions of nitrogen (N) from New Zealand dairy farms are significant but have the potential to be affected by manure management prior to land application. The current work examined whether reducing cattle manure dry matter (DM) from 0.16 high DM (HDM) to 0.06 low DM (LDM), to enhance infiltration and reduce ammonia (NH₃) emissions when applied to grassland, would affect nitrous oxide (N₂O) emissions. Pasture was cut, simulating grazing, and either amended with HDM (173 kg N/ha) or LDM manure (48 kg N/ha) or left unamended. Ammonia emissions from HDM manure were higher than from LDM manure, as a flux or as a percentage of total ammoniacal nitrogen (TAN, i.e. NH₃⁺NH₄⁺) applied, due to more TAN being retained near the soil surface and the higher soil surface pH under HDM manure treatment. Cumulative N₂O emissions over 37 days from HDM plots were higher than from the control but not from the LDM plots. After 5 days, the daily N₂O emission rate was larger from HDM plots than from LDM and control plots. The N₂O fluxes from LDM and HDM treatments did not differ, either as a proportion of TAN applied or as a proportion of total-N applied. Increasing DM contributed to reductions in both oxygen (O₂) availability and relative gas diffusivity, and thus potentially N₂O production. Under the conditions of the current study, lower manure DM content reduced NH₃ emissions but did not increase cumulative losses of N₂O.