Effects of dung and urine amendments on the isotopic content of N2O released from grasslands

The temporal and diurnal changes in nitrous oxide (N2O) fluxes were measure d between 29(th) September and 2(nd) November 1999 from urine and dung patc hes from cattle deposited on grazed grassland. The delta(15)N and delta(18) O values of the N2O emitted from soil from both treatments were examined on four occasions during this period, The diurnal fluxes of N2O were measured by a chamber technique that provides hourly measurement of N2O fluxes. The N-15 and O-18 analysis of N2O were determined by isotope ratio mass spectr ometry. N2O 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 patche s were significantly greater than from the dung, The results showed that ex cretal patches are an important source of atmospheric N2O. 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 soi l temperature changes. The isotopic content of N-15 and O-18 in the N2O sho wed a similar trend to that of the N2O flux. The N-15 and O-18 values of th e N2O emitted from the soil indicated that denitrification was the major pr ocess involved. After heavy precipitation on the 6(th) October, the larger delta(15)N and delta(18)O values suggested a consumption of the N2O by tota l denitrification, Copyright (C) 2000 John Wiley & Sons, Ltd.