Nitrogen Gaseous Emission from Animal Based Agriculture: Effect of Soil Physical Properties

Agriculture has been implicated as an important source of atmospheric nitrous oxide and ammonia emissions. In dairy areas the main source of N is due to the spreading of animal waste on the agricultural land. Fifty to eighty percent of the excreted N from animals occurs in urine with the varying proportion depending on the diet. The main goal of the research was to quantify ammonia and nitrous oxide emissions from urine-treated soils and to relate these results to urinary N-transformation processes in soil. We studied effects of soil texture, air filled porosity, and rate of air exchange. Series of laboratory experiments were carried out in aerobic as well as anaerobic conditions in which synthetic urine was mixed with either fine and coarse sand. Ammonia and nitrous oxide were measured at the time intervals of 20 minutes up to 6 hours. The air flow rate ranged from zero to 2000 ml/min. As expected, most ammonia volatilized during the first hours of the experiment and was well correlated with moisture loss by evaporation. Ammonia volatilization and evaporation rates were greater for coarse rather than fine sand. Consequently the total nitrous oxide emission was higher for the fine sand because more ammonium was available for nitrification and subsequent denitrification. Under no air flow conditions, the input of denitrification to total nitrous oxide production was higher in the fine sand than in the coarse sand at the same moisture content. In all experiments, the most nitrous oxide was emitted within two ranges of oxidation-reduction potential: -50-50 with denitrification-dominant conditions and 250-400 mV with nitrification-dominant conditions.