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Nitrous oxide (N2O) is a greenhouse gas primarily produced in soils by denitrifying and nitrifying organisms. Agricultural soils account for 70% of emissions in the United States, but little data is available for contributions from managed pasture ecosystems. This study focused on the production of N2O in smooth bromegrass (Bromus inermis Leyss.) pastures established on silt loam soils in eastern Nebraska. Thirty smooth bromegrass 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). Herbage sampling was taken the day before sampling by clipping the grass within the anchor to a 10 cm stubble height and oven drying the samples. In 2011, a significant effect between the urine treatment x fertilizer rate and cumulative herbage yield (p = 0.0002) was found. In 2012, the urine treatment significantly affected cumulative herbage yield (p < 0.0001). In 2011, cumulative herbage yield increased with total nitrogen inputs of up to 675 kg N ha-1 compared with 435 kg N ha-1 in 2012. N2O emissions were recorded biweekly from March to October using the Hutchinson and Mosier (1981) vented chamber method in 2011 and 2012. Findings revealed a significant interaction between urine treatment x fertilizer rate interaction and cumulative seasonal flux (p = 0.0061) in 2011 and the urine treatment (p < 0.0001) in 2012. There was a significant exponential relationship between fertilizer rate and cumulative seasonal flux in respect of urine treatment in 2011 (p2O was between 0.518-1.781% for treatments in 2011 and 0.126-0.395% in 2012. The research supports the IPCC recommendations of 1.25% +/- 1% applied N lost as N2O.
Advisor: John A. Guretzky