The effect of N deposition on nitrous oxide and nitric oxide emissions from temperate forest soils

Long-term and short-term N deposition effects on N2O and NO emissions from forest soils were compared. Long-term NH3 deposition (> 20 years) from a poultry farm to a downwind woodland (decreasing from 73 to 18 kg N ha(-1) y(-1), 30 to 110 m downwind of the farm) resulted in the re-emission of 6% and 14% of NH3-N deposited as N2O-N and NO-N, respectively. However, when in short-term (2-3 years) field experiments the atmospheric N deposition to mature conifer plantations was raised by fumigation with NH3 to 15 kg N ha(-1) y(-1) or by acid mist to 48 and 96 kg N ha(-) (1) y(-1) the N deposited was immobilised. In the acid mist experiment more than 2 years of acid mist (48 and 96 kg N ha(-1) y(-1)) were required to significantly increase N2O emissions from -0.3 mu g N2O-N m(-2) h(-1) (control) to 0.5 and 5.7 mu g N2O-N m(-2) h(-1), respectively. This suggests, that N deposition simulation studies in soil ecosystems, which have previously not been exposed to high rates of N (by deposition or fertilisation), need to be long-term. Also, measurements of N2O and/or NO may be a non-destructive, quick indicator of the N status of the soil.