Showing papers by "Arvin R. Mosier published in 1988"

Rates and pathways of nitrous oxide production in a shortgrass steppe

Abstract: Most of the small external inputs of N to the Shortgrass steppe appear to be conserved. One pathway of loss is the emission of nitrous oxide, which we estimate to account for 2.5–9.0% of annual wet deposition inputs of N. These estimates were determined from an N2O emission model based on field data which describe the temporal variability of N2O produced from nitrification and denitrification from two slope positions. Soil water and temperature models were used to translate records of air temperature and precipitation between 1950 and 1984 into variables appropriate to drive the gas flux model, and annual N2O fluxes were estimated for that period. The mean annual fluxes were 80 g N ha−1 for a midslope location and 160 g N ha−1 for a swale. Fluxes were higher in wet years than in dry, ranging from 73 to 100 g N ha−1y−1at the midslope, but the variability was not high. N2O fluxes were also estimated from cattle urine patches and these fluxes while high within a urine patch, did not contribute significantly to a regional budget. Laboratory experiments using C2H2 to inhibit nitrifiers suggested that 60–80% of N2O was produced as a result of nitrification, with denitrification being less important, in contrast to our earlier findings to the contrary. Intrasite and intraseasonal variations in N2O flux were coupled to variations in mineral N dynamics, with high rates of N2O flux occurring with high rates of inorganic N turnover. We computed a mean flux of 104 g N ha−1 y−1 from the shortgrass landscape, and a flux of 2.6 × 109 g N y− from all shortgrass steppe (25 × 106 ha).

Phytotron studies to compare nitrogen losses from corn-planted soil by the 15-N balance or direct dinitrogen and nitrous oxide measurements

Abstract: Containers filled with soil mixed with potassium nitrate highly enriched in 15N were planted with corn (Zea mays L.) and kept in a phytotron under controlled conditions for 79 days. Soil water content was normally maintained at exactly 60% water-holding capacity (−33 kPa), but it was increased several times to 85% (−5 kPa) for short periods to favour denitrification. The soil headspace was sealed from the phytotron atmosphere and aerated by a continuous stream of air. Nitrous oxide emission was measured by estimating the N2O concentration differences in the air entering and leaving the containers. Emission of N2 was estimated by mass spectroscopy from changes in the N2 composition in the temporarily enclosed soil headspace. Both methods were carefully checked for accuracy by different tests. At specific times during the experiment the distribution of 15N between plants and soil was determined and a 15N balance established. Emission of N gases peaked at times of increased water content and reached maxima of 149 and 142 μg N pot−1 day−1 for N2O and N2, respectively. While N losses of 5% ± 2% were indicated by the 15N balance, only 1.1% ± 0.3% loss from 2.7 g applied N was estimated from the N2O and N2 measurements after 79 days. Possible reasons for these differences are discussed.