DENITRIFICATION AND N2O EMISSION FROM URINE-AFFECTED GRASSLAND SOIL

Denitrification and N2O emission rates were measured following two applications of artificial urine (40 g urine-N-2) to a perennial rye-grass sward on sandy soil. To distinguish between N2O emission from denitrification or nitrification, urine was also applied with a nitrification inhibitor (dicyandiamide, DCD). During a 14 day period following each application, the soil was frequently sampled, and incubated with and without acetylene to measure denitrification and N2O emission rates, respectively. Urine application significantly increased denitrification and N2O emission rates up to 14 days after application, with rates amounting to 0.9 and 0.6 g N m(-2) day(-1) (9 and 6 kg N ha(-1) day(-1)), respectively. When DCD was added to the urine, N2O emission rates were significantly lower from 3 to 7 days after urine application onwards. Denitrification was the main source of N2O immediately following each urine application. 14 days after the first application, when soil water contents dropped to 15% (v/v) N2O mainly derived from nitrification. Total denitrification losses during the 14 day periods were 7 g N m(-2), or 18% of the urine-N applied. Total N2O emission losses were 6.5 and 3 g N m(-2), or 16% and 8% of the urine-N applied for the two periods. The minimum estimations of denitrification and N2O emission losses from urine-affected soil were 45 to 55 kg N ha(-1) year(-1) and 20 to 50 kg N ha(-1) year(-1), respectively.