Effects of Mob-Grazing on Soil and Range Quality Vary with Plant Species and Season in a Semiarid Grassland

Aradhana J. Roberts, Nancy C. Johnson

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Mob-grazing involves maintaining high densities of livestock for short periods so that most plants are either eaten or trampled, followed by long rest periods. This practice has been proposed as a mechanism to increase soil carbon (C) storage and range quality. However, mob-grazing has not universally achieved these objectives, possibly because many factors influence the effects of grazing on soil C dynamics and vegetation. This study examines factors that may mediate grazing impacts on soil C by comparing plant cover and the seasonal dynamics of roots, soil variables, and mycorrhizal fungal hyphae in experimental plots treated with traditional grazing, annual mob-grazing or no grazing for 18 yr. Root and soil variables were measured directly underneath a C4 grass, a C3 grass, and a forb up to 5 × during a 13-mo period. Mob-grazing did not influence total soil C, but it significantly increased soil organic matter (SOM), fine particulate organic matter, and nitrogen-15 (δ15N). Furthermore, mob-grazing increased soil compaction, decreased soil aggregate stability, decreased soil moisture, and tended to increase the abundance of two invasive plant species: Salsola tragus and Bromus tectorum. Soil compaction, soil aggregate stability, root biomass, particulate organic matter, and percent soil C and N varied significantly across seasons and among plant species. The density of mycorrhizal fungal hyphae varied with season but not with grazing treatment. A significant grazing by date interaction in root biomass and soil carbon-13 (δ13C) suggests that root dieback and inputs of pulverized plant material with a higher δ13C signature could be the source of higher SOM in mob-grazed plots. Compared with ungrazed plots, traditionally grazed plots had higher SOM without the adverse impacts on vegetation and soil properties observed in the mob-grazed plots. No single management strategy is universally beneficial. Range managers should carefully weigh the pros and cons of mob-grazing because, although it can increase SOM in surface soils, it may also negatively impact soil structure and composition of vegetation.

Original languageEnglish (US)
Pages (from-to)139-149
Number of pages11
JournalRangeland Ecology and Management
StatePublished - Nov 2021


  • Artemisia frigida
  • Bouteloua gracilis
  • Pascopyrum smithi
  • Savory method
  • mycorrhizal fungal hyphae
  • soil organic matter

ASJC Scopus subject areas

  • Ecology
  • Animal Science and Zoology
  • Nature and Landscape Conservation
  • Management, Monitoring, Policy and Law


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