Nitrous Oxide Emissions From Smooth Bromegrass Pasture Under Nitrogen Fertilizer and Ruminant Urine Application in Eastern Nebraska.

Nitrous oxide (N₂O) is a greenhouse gas primarily produced in soils by denitrifying and nitrifying organisms.  In terms of global warming potential (GWP), N₂O has 310 times the GWP of carbon dioxide (CO₂).  Atmospheric N₂O concentrations have increased by 18% since the industrial revolution with agricultural soils responsible for 70% of emissions in the United States.  Tracking N₂O emissions in the United States prepares the country for future legislation and carbon budgeting.  Although the measurement of N₂O has become more focused in the last 20 years, little data has been collected in managed pasture ecosystems.  This study focused on the production of N₂O in smooth brome (Bromus inermis Leyss.) pastures established on silt loam soils in eastern Nebraska. Thirty smooth brome plots (1.5m x 1.5m) were treated with five different fertilizer treatments (0, 45, 90, 135, and 180 kg N/ha) and two urine treatments (urine and no urine).  N₂O emissions were recorded biweekly from March to October using the Hutchinson and Mosier (1981) vented chamber method. Preliminary findings revealed a significant interaction between Nitrogen fertilizer rate (p<0.005), urine application (p <0.001), and sampling date (p<0.0001).  Both N and urine treatments resulted in higher N2O emissions compared to control plots.  This study found ideal conditions for denitrifying and nitrifying activity occurred in soil at 15.5^oC with 55% soil moisture which resulted in N₂O emissions up to 983.88 g N/ha/day.  The research discovered higher N₂O emissions than cited in previous studies and significant daily losses raise questions about timing of sampling and further research.