Long‐Term Grazing Alters Soil Trace Gas Fluxes from Grasslands in the Foothills of the Rocky Mountains, Canada

Abstract

Long-term cattle grazing may degrade grassland soils, but how soil CO 2 , CH 4 and N 2 O fluxes respond to long-term cattle grazing is poorly understood. Therefore, we quantified soil CO 2 , CH 4 and N 2 O fluxes in response to four levels (none, light, heavy, very heavy) of long-term (>65 years) cattle grazing on a rough fescue grassland in the foothills of the Rocky Mountains, Canada over three grazing seasons. The grazed grassland soils emitted 37 to 51% more CO 2 than non-grazed soils. Grazed grassland soils were small CH 4 sinks and small N 2 O sources each season, and their cumulative fluxes were significantly affected by a cattle stocking rate × year interaction, indicating the grazing effect was influenced by environmental conditions. Soil CH 4 uptake was negatively correlated with soil moisture (r = À0·59). The 2013 grazing season had about 41% greater precipitation than average and grazing significantly decreased CH 4 uptake 31 to 38% compared with non-grazed soils. The N 2 O emissions were 122 to 179% greater with heavy and very heavy grazing than none in the wet season, unaffected by grazing in the normal precipitation season and 72% lower with light grazing than none in the dry season. Predicting trace gas fluxes from grazed grassland soils across space and time is difficult because of interactions among weather conditions, edaphic properties and grazing intensity. However, long-term cattle grazing increased soil CO 2 fluxes, while the grazing effect on CH 4 uptake depended on precipitation and the soil N 2 O flux responded as a function of grazing intensity and precipitation.

Slope position regulates response of carbon and nitrogen stocks to cattle grazing on rough fescue grassland

“…At the same time, grazing may facilitate the growth of plants with shallow roots (Ingram et al 2008) and hence increase the surface layer root C and N stocks. With VH treatment, lower litter and standing crop C stocks may be related to the decrease of aboveground primary production (Li et al 2008;Gao et al 2018) and a smaller mass of residual crop following grazing. Livestock dung and urine could increase the soil available N (Frank and Evans 1997) and hence increase plant N content (Mikola et al 2009).…”

“…On the other hand, the hoof action of livestock may influence C and N storage through its effects on litter decomposition rate and soil physical status (Semmartin et al 2008). Soil is the main reservoir of C and N in grassland ecosystems, and previous studies have shown that livestock grazing alters the accumulation and release of soil C and N (Tanentzap and Coomes 2012;Gao et al 2018). However, the direction and magnitude of grazing effects are highly contextdependent and regulated by the complex interactions among grazing strategy, climate, and soil (McSherry and Ritchie 2013).…”

Effects of Grazing Management on Spatio-Temporal Heterogeneity of Soil Carbon and Greenhouse Gas Emissions of Grasslands and Rangelands: Monitoring, Modelling and Upscaling

“…Counter-intuitive, no significant differences were found among the three grazing treatments in the top of the slope. Gao et al [47] investigated soil trace gas fluxes from grasslands in the foothills of the Rocky Mountains, Alberta. Grazed grassland soils had 37 to 51% greater CO2 emissions?…”

Effects of Grazing Pattern on Ecosystem Respiration and Methane Flux in a Sown Pasture in Inner Mongolia, China

“…For example, a study, in an alpine steppe on the Tibetan Plateau, China, thought that no grazing enhanced CH 4 uptake by 17.8% and 33.8% in 2009 and 2010, respectively, while its effect on CO 2 emission (ecosystem respiration) was not significant [55]. Gao et al reported that long-term cattle grazing increased soil CO 2 fluxes, while the grazing effect on CH 4 uptake depended on precipitation [56]. The effects of grazing on ecosystem respiration and methane flux are complex.…”