Using alternative forage species to reduce emissions of the greenhouse gas nitrous oxide from cattle urine deposited onto soil

Grazed pastures are a major contributor to emissions of the greenhouse gas nitrous oxide (N2O) and urine deposition from grazing animals is the main source of the emissions. Incorporating alternative forages into grazing systems could be an approach for reducing N2O emissions through mechanisms such as release of nitrification inhibitors from roots and increased root depth. Field plot and lysimeter trials were conducted in a free draining Horotiu silt loam soil to test whether two alternative forage species, plantain (Plantago lanceolate L.) and lucerne (Medicago sativa L.), could reduce N2O emissions relative to traditional pasture species, white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). The amounts of N2O emitted from the soil below each forage species, which all received the same cow urine at the same rates, was measured using an established static chamber method. Total N2O emissions from the plantain, lucerne and perennial ryegrass controls (without urine application) were generally very low, but emissions from the white clover control was significantly higher. When urine was applied in autumn or winter N2O emissions from plantain were lower compared with those from perennial ryegrass or white clover, but N2O emissions from plantain and perennial ryegrass were similar when urine was applied in summer. Differences in emissions between lucerne and perennial ryegrass after urine application were strongly dependant on season. Incorporation of plantain into grazed pasture could be an approach to reduce N2O emissions. However, further work is required to understand the mechanisms for the reduced emissions and the effects of environmental conditions in different seasons.