Effects of dung and urine amendments on the isotopic content of N(2)O released from grasslands.

The temporal and diurnal changes in nitrous oxide (N(2)O) fluxes were measured between 29(th) September and 2(nd) November 1999 from urine and dung patches from cattle deposited on grazed grassland. The delta(15)N and delta(18)O values of the N(2)O emitted from soil from both treatments were examined on four occasions during this period. The diurnal fluxes of N(2)O were measured by a chamber technique that provides hourly measurement of N(2)O fluxes. The (15)N and (18)O analysis of N(2)O were determined by isotope ratio mass spectrometry. N(2)O fluxes from the excreta patches were large, with peak emissions up to 1893 ng N m(-2) s(-1) occurring after heavy precipitation, measured one month after the treatment applications. Emissions from the urine patches were significantly greater than from the dung. The results showed that excretal patches are an important source of atmospheric N(2)O. The flux pattern showed a strong diurnal variation with maximum fluxes generally occurring in late afternoon or early morning, and generally not in phase with the soil temperature changes. The isotopic content of (15)N and (18)O in the N(2)O showed a similar trend to that of the N(2)O flux. The (15)N and (18)O values of the N(2)O emitted from the soil indicated that denitrification was the major process involved. After heavy precipitation on the 6(th) October, the larger delta(15)N and delta(18)O values suggested a consumption of the N(2)O by total denitrification. Copyright 2000 John Wiley & Sons, Ltd.