Location: Agroecosystem Management ResearchTitle: Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application Author
Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2014
Publication Date: 2/25/2014
Citation: Snell, L.K., Guretzky, J.A., Jin, V.L., Drijber, R.A., Mamo, M. 2014. Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application. Nutrient Cycling in Agroecosystems. 98:223-234. DOI: 10.1007/S10705-014-9607-Z. Interpretive Summary: Pasture management in eastern Nebraska supports the state’s $12 billion beef cattle industry, which is the largest single industry in Nebraska and ranks 1st in commercial red meat production in the United States. Little is known about how pasture fertilization rates and grazer urine inputs in eastern Nebraska affect forage grass production or pasture soil emissions of nitrous oxide (N2O), a powerful temperature-forcing greenhouse gas. This research addresses those knowledge gaps. Smooth bromegrass production and soil N2O emissions increased with higher N rate in 2011, but was severely limited by extreme drought in 2012. Grazer urine inputs in both year provided moisture, nitrogen, and carbon sources that promoted plant growth and increased soil N2O emissions. The key implication of research results is that management practices that increase plant and animal nitrogen use efficiencies can also decrease soil N2O emissions.
Technical Abstract: Agricultural soils contribute significantly to nitrous oxide (N2O) emissions, but little data is available on N2O emissions from smooth bromegrass (Bromus inermis Leyss.) pastures. This study evaluated soil N2O emissions and herbage accumulation from smooth bromegrass pasture in eastern Nebraska, USA. Nitrous oxide emissions were measured biweekly from March to October in 2011 and 2012 using vented static chambers on smooth bromegrass plots treated with a factorial combination of five N fertilizer rates (0, 45, 90, 135, and 180 kg ha-1) and two ruminant urine treatments (urine and distilled water). Urine input strongly affected daily and cumulative N2O emissions in both years, but responses to N fertilizer rate depended on growing season rainfall. In 2011, when rainfall was normal, cumulative N2O emissions increased exponentially with N fertilizer rate. During drought in 2012, however, N fertilizer rate had no effects on daily and cumulative N2O flux. Herbage accumulation ranged from 4.46 Mg ha-1 in unfertilized pasture without urine input to 16.01 Mg ha-1 in pasture supplied with 180 kg N ha-1 and urine in 2011. In 2012, plots treated with urine had 2.2 times as much herbage accumulation than plots treated with distilled water but showed no response to N fertilizer application. The amount of applied N lost as N2O ranged from 0.52 to 1.78% in 2011 and 0.13 to 0.40% in 2012. Our research supports the Intergovernmental Panel on Climate Change (IPCC) recommendations of 1.25% +/- 1% applied N lost as N2O, though variability in weather can impact this percentage year-to-year.