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 decades, and they might influence the consumption of atmospheric CH4. We report on measurements of N2O and CH4 exchange of a pasture soil, as influenced by droppings of a grazing cattle (Bos taurus) herd. Nitrous oxide and methane fluxes in pasture soil were largely determined by the emission rates from cattle excrement with dung patches being hot spots of CH4production 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 rumen of the cattle. Total N2O-N losses from the droppings were equivalent to 3.2% of the nitrogen excreted. Based on global data of total nitrogen 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 -1.18 teragrams N2O-N per year, indicating that grazing cattle excretory products are one of the most important sources of atmospheric nitrous oxide. Our work suggests that these sources have been drastically underestimated.