Effects of Mob-Grazing on Soil and Range Quality Vary with Plant Species and Season in a Semiarid Grassland
(2021) In Rangeland Ecology and Management 79. p.139-149- Abstract
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... (More)
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.
(Less)
- author
- Roberts, Aradhana J. LU and Johnson, Nancy C.
- organization
- publishing date
- 2021-11
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Artemisia frigida, Bouteloua gracilis, mycorrhizal fungal hyphae, Pascopyrum smithi, Savory method, soil organic matter
- in
- Rangeland Ecology and Management
- volume
- 79
- pages
- 11 pages
- publisher
- Society of Environmental Toxicology and Chemistry
- external identifiers
-
- scopus:85115036276
- ISSN
- 1550-7424
- DOI
- 10.1016/j.rama.2021.04.008
- language
- English
- LU publication?
- yes
- id
- 35c94509-b30e-4329-8fd1-3db758f569e7
- date added to LUP
- 2021-09-28 11:44:31
- date last changed
- 2023-02-21 11:21:19
@article{35c94509-b30e-4329-8fd1-3db758f569e7,
abstract = {{<p>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 C<sub>4</sub> grass, a C<sub>3</sub> 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 (δ<sup>15</sup>N). 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 (δ<sup>13</sup>C) suggests that root dieback and inputs of pulverized plant material with a higher δ<sup>13</sup>C 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.</p>}},
author = {{Roberts, Aradhana J. and Johnson, Nancy C.}},
issn = {{1550-7424}},
keywords = {{Artemisia frigida; Bouteloua gracilis; mycorrhizal fungal hyphae; Pascopyrum smithi; Savory method; soil organic matter}},
language = {{eng}},
pages = {{139--149}},
publisher = {{Society of Environmental Toxicology and Chemistry}},
series = {{Rangeland Ecology and Management}},
title = {{Effects of Mob-Grazing on Soil and Range Quality Vary with Plant Species and Season in a Semiarid Grassland}},
url = {{http://dx.doi.org/10.1016/j.rama.2021.04.008}},
doi = {{10.1016/j.rama.2021.04.008}},
volume = {{79}},
year = {{2021}},
}