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Title: Nitrous oxide and methane fluxes from cattle excrement on C3 pasture and C4-dominated shortgrass steppe

Author
item Nichols, Kristopher
item Del Grosso, Stephen - Steve
item Derner, Justin
item FOLLETT, RONALD - Retired ARS Employee
item ARCHIBEQUE, SHAWN - Colorado State University
item Stewart, Catherine
item PAUSTIAN, KEITH - Colorado State University

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2016
Publication Date: 3/26/2016
Citation: Nichols, K.L., Del Grosso, S.J., Derner, J.D., Follett, R., Archibeque, S., Stewart, C.E., Paustian, K. 2016. Nitrous oxide and methane fluxes from cattle excrement on C3 pasture and C4-dominated shortgrass steppe. Agriculture Ecosystems and the Environment. Vol 225: 104–115. doi:10.1016/j.agee.2016.03.026.

Interpretive Summary: Grazers play a major role in nutrient cycling of grassland ecosystems through biomass removal and deposition of urine and feces. We studied the effects of cattle urine and feces patches on greenhouse gas fluxes on cool-season (C3), Russian wildrye pasture, and warm-season (C4)-dominated native rangeland. Greenhouse gas measurements were conducted over a 2 year period, June 2012 to June 2014, which included the severe drought of 2012. Nitrous oxide emissions from urine patches were approximately 100% greater than those from the control plots, whereas emissions from feces were over 150% greater than the control plots. Cumulative nitrous oxide emissions were 55% greater from feces relative to urine patches on native rangeland and 25% greater on Russian wildrye pasture. However, the proportion of urine and feces nitrogen emitted as nitrous oxide did not differ on native rangeland (0.13 and 0.13%) and Russian wildrye pasture (0.14 and 0.11%). These proportions are substantially less than the standard default (2%) used to calculate nitrous oxide emissions from urine and feces on pasture, indicating that using the standard default would result in a significant overestimation of emissions from urine and feces patches deposited on shortgrass steppe native rangeland and cool-season pasture during drought conditions. Cumulative net methane uptake was greater for all treatments on native rangeland compared to Bozoisky-select pasture. Cumulative net CH4 uptake rates per unit area on native rangeland were 68% greater from urine compared to feces patches and 86% greater on pasture.

Technical Abstract: Grazers play a major role in nutrient cycling of grassland ecosystems through biomass removal and excrement deposition (urine and feces). We studied the effects of cattle excrement patches (cattle urine at 430 and feces at 940 kg N ha-1) on nitrous oxide (N2O) and methane (CH4) fluxes using semi-static chambers on cool-season (C3), Bozoisky-select (Psathyrostachys juncea) pasture, and warm-season (C4)-dominated native rangeland. Trace gas measurements were conducted over a 2 year period, June 2012 to June 2014, which included the severe drought of 2012. Nitrous oxide emissions from urine patches were approximately 100% greater than those from the control plots (1.17 vs. 0.61 kg N2O-N ha-1 native rangeland and 1.25 vs. 0.65 Bozoisky-select), whereas emissions from feces were over 150% greater than the control plots (1.81 vs 0.61 kg N2O-N ha-1 native rangeland and 1.66 vs. 0.65 Bozoisky-select). Cumulative N2O emissions were 55% greater from feces relative to urine patches (1.81 vs. 1.17 kg N2O-N ha-1) on native rangeland and 25% greater on Bozoisky-select pasture (1.66 vs.1.25). However, the emission factors (EF) for urine and feces did not differ on native rangeland (0.13 and 0.13%) and Bozoisky-select pasture (0.14 and 0.11%). These EFs are substantially less than the IPCC Tier 1 Default EF (2%) for manure deposited on pasture, indicating that the IPCC Tier 1 Default EF would result in a significant overestimation of emissions from urine and feces patches deposited on SGS native rangeland and cool-season pasture during drought conditions. Cumulative net CH4 uptake was greater for all treatments on native rangeland compared to Bozoisky-select pasture (urine: -2.73 vs. -2.16, feces: -0.88 vs. -0.30, blank: -3.60 vs. -3.15 kg CH4-C ha-1). Cumulative net CH4 uptake rates per unit area on native rangeland were 68% greater from urine compared to feces patches (-2.73 vs. -0.88 kg CH4-C ha-1) and 86% greater on pasture (-2.16 vs. -0.30). {GRACENet}