Grassland plant species and cultivar effects on nitrous oxide emissions after urine application

We tested whether plant species identity influenced emissions of nitrous oxide (N2O) in response to the addition of urine at a rate of 530 kg nitrogen (N) ha−1. The plants tested are all used in temperate pastoral agriculture and comprised 11 C3 grasses, 3 forbs and 2 legumes with controls of bare ground and a standard ryegrass/white clover mixture used in the region. Total N2O emitted over 6 weeks after the application of cattle urine was highest in the bare ground. Plant identity was important with emissions ranging from an average of 0.67 kg N2ONha−1 for the Italian ryegrass Grasslands Moata (Lolium multiflorum) to 3.20 kg N2O-N ha−1 for the upland brome Grasslands Gala (Bromus stamineus). The 4 perennial ryegrass (Lolium perenne) cultivars had generally low emissions (average of 1.02 kg N2O-N ha−1) and the white clover (Trifolium repens) cultivars high emissions (average of 2.86 kg N2O-N ha−1). Plants with high N uptake rates had low N2O emissions. However, this was not always due to a high N uptake rate per se as during the first 2 weeks after urine was applied, when N2O emissions were at their highest, soil mineral N was in excess of plant N demand. It seems that some traits related to a high plant N uptake, such as low soil nitrification potential, might be important in driving differences in emissions associated with different plant species.