NITROUS-OXIDE EMISSIONS FROM EXCRETA APPLIED IN A SIMULATED GRAZING PATTERN

N2O emissions were measured From cattle dung and urine applied to six separate experimental areas over a period of 15 months, to represent d istinct components of a grazing season. Application of livestock excre ta increased N2O emissions significantly over that measured from contr ol (untreated) plots and fluxes up to 290 mu g N m(-2) h(-1) from dung and 192 mu g N m(-2) hr(-1) from urine were measured. No significant correlations were observed between N2O fluxes and environmental factor s: such as rainfall and soil mineral-N. This was attributed to the spe cific physical and biogeochemical processes in the excreta that might override other environmental factors at our plots. Total N2O-N losses from dung and urine patches over 100 d represented up to 0.53% and 1% respectively, of the N excreted. The average annual N2O fluxes were ap proximately five times greater from the urine patches than from the du ng, and from the excreta deposited during wet conditions (autumn) than during dry conditions (summer). Our results suggest that excreta depo sited on grassland from grazing animals is an important source of N2O, and can contribute up to 22% of the total N2O emission from U.K. gras sland. (C) 1998 Elsevier Science Ltd. All rights reserved.