The potential of using alternative pastures, forage crops and gibberellic acid to mitigate nitrous oxide emissions

Abstract

© 2016, Springer-Verlag Berlin Heidelberg. Purpose: In grazed pastures, nitrous oxide (N₂O), a powerful greenhouse gas and an ozone depletion substance, is mostly emitted from animal excreta, particularly animal urine-N returned to the soil during grazing. We conducted a series of four field lysimeter and plot experiments to assess the potential of using gibberellic acid (GA) and/or alternative pastures or forage crops to mitigate N₂O emissions from outdoor dairy farming systems. Materials and methods: Pasture and forage plants assessed in the experiments included Italian ryegrass (Lolium multiflorum L.), lucerne (Medicago sativa L.), diverse pastures (including plantain (Plantago lanceolata L.), chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.)), fodder beet (Beta vulgaris L.), kale (Brassica oleracea L.), as well as the standard perennial ryegrass and white clover (RG/WC) pastures. N₂O was determined using a standard static chamber method in the field either on top of lysimeters or field plots. Results and discussion: The results showed that the application of GA to urine-treated lysimeters with Italian ryegrass, lucerne or RG/WC pastures did not result in lower N₂O emissions. However, the use of diverse pastures which included plantain with a lower urine-N loading rate at about 500 kg N ha⁻¹ significantly decreased N₂O emissions by 46 % compared with standard RG/WC with a urine-N loading rate at 700 kg N ha⁻¹. However, when urine-N was applied at the same rates (at 500 or 700 kg N ha⁻¹), the N₂O emissions were similar between the diverse and the standard RG/WC pastures. This would indicate that it is the N-loading rate in the urine from the different pastures that determines the N₂O emissions from different pastures or forages, rather than the plants per se. The N₂O emissions from cow urine from fodder beet were 39 % lower than from kale with the same urine-N application rate (300 kg N ha⁻¹). Conclusions: These results suggest that N₂O emissions can potentially be reduced by incorporating diverse pastures and fodder beet into the grazed pasture farm system. Further studies on possible mechanisms for the lower N₂O emissions from the different pastures or forages would be useful.