Cattle-induced hotspot impacts on N2O and CH4 fluxes in shortgrass steppe

Authors: Del Grosso, Stephen; NICHOLS, KRISTOPHER - Natural Resources Conservation Service (NRCS, USDA); Delgado, Jorge; Derner, Justin; Augustine, David

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2025
Publication Date: 8/22/2025
Citation: Del Grosso, S.J., Nichols, K.L., Delgado, J.A., Derner, J.D., Augustine, D.J. 2025. Cattle-induced hotspot impacts on N2O and CH4 fluxes in shortgrass steppe. Nutrient Cycling in Agroecosystems. https://doi.org/10.1007/s10705-025-10426-4.
DOI: https://doi.org/10.1007/s10705-025-10426-4

Interpretive Summary: Grassland soils managed for grazing absorb methane (CH4) and emit nitrous oxide (N2O). Both CH4 and N2O act as greenhouse gases while N2O also depletes ozone in the upper atmosphere. Scientists from USDA ARS and NRCS previously observed enhanced N2O emissions from fresh patches of urine and manure in grassland but are there long term effects of cattle congregating in pasture hotspots near water tanks? Hotspots receive disproportionate manure and urine deposits which enhanced N2O emissions by 5-10 times compared to centers but CH4 uptake was not substantially altered. Although hotspots make up a small portion (< 2%) of total pasture area, they were responsible for about 4-15% of pasture level N2O. After accounting for global warming potentials, CH4 uptake exceeded N2O emissions so these pasture soils are a net GHG sink.

Technical Abstract: Grassland soils managed with livestock grazing can act as sources and sinks for methane (CH4) and nitrous oxide (N2O), but, in aggregate, are typically a source of N2O and a sink for CH4. Previously, we observed higher N2O losses from fresh patches of urine and manure in shortgrass steppe compared to controls receiving no excreta inputs while CH4 was a short-term source from manure patches but remained a sink with urine application. Here, we investigate legacy impacts of'>'75 years of cattle congregating in pasture hotspots near corners and water tanks under traditional, season-long (mid-May to October) and short term adaptive rotational grazing management on soil N2O and CH4 fluxes. As expected, soil NO3 and NH4 were elevated in both long-term traditional grazed and adaptively grazed pasture hotspots. Similarly, N2O emissions over all three years of the study (2015–2017) were higher in hotspots for both traditional and adaptively grazed pastures. Contrary to our hypothesis, CH4 uptake in hotspots was less than pasture centers only during 2015. Although hotspots make up a small portion (<'2%) of total pasture area, they were responsible for about 4–15% of pasture level N2O because emissions were 5–10 times higher than pasture centers on a unit area basis. When aggregating to the pasture level, the CO2 equivalents of the CH4 sink exceeded those of the N2O source implying a net soil GHG sink in this semiarid grazed grassland.