Nitrous oxide and ammonia emissions from urine-treated soils: Texture effect

Urine-treated soils have been implicated as an important source of gaseous N losses to the atmosphere. The goal of our research was to quantify NH3 and N2O emissions from urine under different simplified and controlled soil conditions and to relate these results to urinary-N transformation processes in soil. We studied the influence of soil texture (coarse vs. fine sand), moisture distribution with depth, air-filled pore space, and rate of air movement, which affected both soil drying processes and emission rates. Laboratory experiments were performed with synthetic urine in both aerobic and anaerobic conditions. Texture was the most important factor controlling NH3 volatilization and N2O emission factors in urine-treated sands. Generally, the finer the sand texture, the higher the input of denitrification to the total N2O emissions; however, the air-filled pore space threshold, below which denitrification became dominant, was greater in coarse sand. In addition, the evaporation rate of the urine water component was found to be an important parameter in total NH3 and N2O emissions. Ammonia volatilization occurred during the first day of the treatments, with volatilization rates closely related to evaporation rates in both sand textures. Finer sand texture caused reductions in the urine evaporation rate and therefore in NH3 volatilization rates. Urine evaporation increased air-filled pore space, thereby improving aeration conditions in the sand that contribute to nitrification dominance of N2O production. Moreover, evaporation of urine, enriched with dissolved N2O, increased total N2O emission. Results from these simplified experiments need confirmation under field soil conditions.