Soil nitrous oxide and nitric oxide emissions as indicators of elevated atmospheric N deposition rates in seminatural ecosystems

Elevated N deposition caused by ammonia emissions from poultry and pig farms, and supplemented N concentrations in acid mist in field and chamber experiments increased soil available NH4+ and NO3− concentrations and emissions of N2O and NO. In a ‘pristine’ soil, not previously exposed to high N deposition rates, an initial threshold of 40 kg N ha−1 year −1 was required to increase N2O emissions. For all data described here on average 0.76% (range 0.2 to 15%) of the elevated N deposited was emitted as N2O. For soils exposed to long-term and large N deposition rates N2O losses>3% of the N deposition rate were calculated. This suggests that N2O losses of more than 3% of the N input can be indicative of soil ecosystems where the N input exceeds its demand. For NO a more limited data set showed losses ranging from 1.3 to 20% of the elevated N input. It was calculated that NH3 emissions from all intensive pig and poultry farms in Great Britain accounted for 18 t N2O---N year−1 and that poultry farms accounted for less than 3 t NO---N year−1.