NITROUS-OXIDE FLUX FROM NITRIC-ACID-TREATED CATTLE SLURRY APPLIED TO GRASSLAND UNDER SEMI-CONTROLLED CONDITIONS

Nitrous oxide (N2O) fluxes from cattle slurry after surface application to grassland were measured under semi-controlled environmental conditions during three periods in 1991. Three types of cattle slurry were examined: untreated slurry and slurries treated with nitric acid (HNO3) to pH 6.0 and 4.5. Treatment with HNO3 is a proposed technique to reduce ammonia volatilization from slurry during storage, and during and after surface application. N2O flux was determined one to four times a day for 7 to 18 days after application of 0.64 to 3.8 kg slurry m-2. Slurry-derived fluxes were much higher from treated slurries than from untreated slurries. Cumulative N2O losses ranged from less than 0.2 % of the mineral N applied via untreated slurry to a maximum of 3.4 % of mineral N for treated slurry of pH 6.0, which was stored for one week before application. N2O fluxes from slurry of pH 6.0 and those from slurry of pH 4.5 were similar, provided that the pH-6.0 slurry was treated one hour before application. Differences between treatments with treated slurry and those with calcium ammonium nitrate were relatively small; apparently the amount of NO3- N applied controlled the N2O flux. Regular irrigation strongly increased N2O fluxes.