Short-term carbon and nitrogen cycling in urine patches assessed by combined carbon-13 and nitrogen-15 labelling.

Summary

Deposition of urine and dung by grazing animals is a strong source for N2O production and evolution in grass pastures. Investigations have shown that at least 20% of the annual losses of N2O from a grazed pasture may be associated with urine patches. Moreover, it is well known that urine depositions causes plant damage (scorching) and root death. It can therefore be hypothesized that organic C is released, which may further stimulate the production of N2O. In this study we have used combined 13C-pulse labeling and 15N-labeled urine in order to determine the amount of plant derived C respired in response to the urine application and assess the N2O emission factor from urine patches. Over a six weeks course the cumulated amount of CO2 evolved equaled the quantity of organic C added with the urine, however, the amount of non-plant derived carbon approximated 50% of the total CO2 release. Emissions of N2O-N amounted 0.20% to 0.26% in urine patches, and 0.14% with mineral N. These results indicate that more urine-N is susceptible to transformation and losses as N2O than mineral N.