Nitrous oxide and ammonia emissions from cattle excrement on C3 pasture and C4-dominated shortgrass steppe

Authors: Nichols, Kristopher; Del Grosso, Stephen - Steve; Derner, Justin; Follett, Ronald; ARCHIBEQUE, SEAN - Colorado State University; Delgado, Jorge; PAUSTIAN, KEITH - Colorado State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2018
Publication Date: 5/2/2018
Citation: Nichols, K.L., Del Grosso, S.J., Derner, J.D., Follett, R.F., Archibeque, S., Delgado, J.A., Paustian, K. 2018. Nitrous oxide and ammonia emissions from cattle excrement on C3 pasture and C4-dominated shortgrass steppe. Journal of Environmental Quality. 47:419–426. doi:10.2134/jeq2017.12.0463.
DOI: https://doi.org/10.2134/jeq2017.12.0463

Interpretive Summary: Grazing cattle redistribute nitrogen consumed in forage through urine and feces patches. The high concentration of nitrogen in these patches often exceeds the uptake demands of the local plant community, thereby providing ideal conditions for losses of reactive nitrogen. We studied the effect of actual cattle urine and feces patches on nitrous oxide and ammonia gas emissions from cool-season (C3), Bozoisky-select pasture and C4-dominated native rangeland of the shortgrass steppe. Cumulative ammonia volatilization was 351 and 164% greater on C3 pasture compared to C4-dominated native rangeland from the urine and feces treatments, respectively. Contrary to previous findings, cumulative ammonia volatilization from the feces treatment was significantly greater than baseline levels. The average ammonia emission factors for urine and feces combined was 16.5 and 6.0% on C3 pasture and C4-dominated native rangeland, respectively. Nitrous oxide emission factors were 0.20 and 0.08 percent for the urine treatment and 0.07 and 0.03 percent for the feces treatment on C3 pasture and C4-dominated native rangeland, respectively. Our findings suggest that using the IPCC Tier 1 default emission factor (2%) to estimate nitrous oxide emissions from cattle excrement patches at the shortgrass steppe would result in a significant overestimation for these dryland systems. In contrast, the observed ammonia emissions are consistent with the IPCC Tier 1 default assumption that 20% of excrement nitrogen is volatilized as ammonia plus nitrogen oxides.

Technical Abstract: Grazing cattle redistribute nitrogen (N) consumed in forage through urine and feces patches. The high concentration of N in these patches often exceeds the uptake demands of the local plant community, thereby providing ideal conditions for losses of reactive N. We studied the effect of actual cattle urine (1002 kg N ha-1) and feces (1021 kg N ha-1) patches on nitrous oxide (N2O) and ammonia (NH3) emissions from cool-season (C3), Bozoisky-select (Psathyrostachys juncea), pasture and C4-dominated native rangeland of the shortgrass steppe. Cumulative NH3 volatilization was 351 and 164% greater on C3 pasture compared to C4-dominated native rangeland from the urine (274 vs. 78 kg NH3-N ha-1) and feces (59 and 36 kg NH3-N ha-1) treatments, respectively. Contrary to previous findings, cumulative NH3 volatilization from the feces treatment was significantly greater than baseline levels. The average NH3 emission factors for urine and feces combined was 16.5 and 6.0% on C3 pasture and C4-dominated native rangeland, respectively. Nitrous oxide emission factors were 0.20 and 0.08 percent for the urine treatment and 0.07 and 0.03 percent for the feces treatment on C3 pasture and C4-dominated native rangeland, respectively. Our findings suggest that using the IPCC Tier 1 default EF (2%) to estimate N2O emissions from cattle excrement patches at the shortgrass steppe would result in a significant overestimation for these dryland systems. In contrast, the observed NH3 emissions are consistent with the IPCC Tier 1 default assumption that 20% of excrement N is volatilized as NH3+NOx.