NITROUS-OXIDE EMISSIONS FROM GRAZED GRASSLAND

Grazing animals on managed pastures and rangelands have been identifie d recently as significant contributors to the global N2O budget. This paper summarizes relevant literature data on N2O emissions from dung, urine and grazed grassland, and provides an estimate of the contributi on of grazing animals to the global N2O budget. The effects of grazing animals on N2O emission are brought about by the concentration of her bage N in urine and dung patches, and by the compaction of the soil du e to treading and trampling. The limited amount of experimental data i ndicates that 0.1 to 0.7% of the N in dung and 0.1 to 3.8% of the N in urine is emitted to the atmosphere as N2O. There are no pertinent dat a about the effects of compaction by treading cattle on N2O emission v et Integral effects of grazing animals have been obtained by comparing grazed pastures with mown-only grassland. Grazing derived emissions, expressed as per cent of the amount of N excreted by grazing animals i n dung and urine, range from 0.2 to 9.9%, with an overall mean of 2%. Using this emission factor and data statistics from FAO for numbers of animals, the global contribution of grazing animals was estimated at 1.55 Tg N2O-N per year. This is slightly more than 10% of the global b udget.