INFLUENCE OF CATTLE WASTES ON NITROUS-OXIDE AND METHANE FLUXES IN PASTURE LAND

Agricultural practices are assumed to contribute significantly to the increase in atmospheric N2O concentrations observed in the last decade s, and they might influence the consumption of atmospheric CH4. We rep ort on measurements of N2O and CH4 exchange of a pasture soil, as infl uenced by droppings of a grazing cattle (BOS taurus) herd. Nitrous oxi de and methane fluxes in pasture soil were largely determined by the e mission rates From cattle excrement with dung patches being hot spots of CH4 production and urine-affected areas showing extremely high N2O release rates. Methane emissions from dung patches (0.778 g CH4-C per animal and day) were insignificant when compared with those from the r umen of the cattle. Total N2O-N losses from the droppings were equival ent to 3.2% of the nitrogen excreted. Based on global data of total ni trogen excretion by dairy cattle, non-dairy cattle, buffalo (Syncerus caffer), and bison during grazing, we estimate the global N2O emission from this source to be similar to 1.18 teragrams N2O-N per year, indi cating that grazing cattle excretory products are one of the most impo rtant sources of atmospheric nitrous oxide. Our work suggests that the se sources have been drastically underestimated.