Document Type

Thesis - Open Access

Award Date

2019

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

Lora B. Perkins

Abstract

Historic grazing and fire regimes have been altered with the development of the livestock industry in the Northern Great Plains and have resulted in a reduction of diversity across all scales. As alternative land surface disturbances are developed to combat the loss of diversity, their potential to serve as a sustainable land surface disturbance should be evaluated. To determine the ability of an alternative grazing strategy to serve as a sustainable land surface disturbance, the reaction of the soil microbial community and soil hydrological processes should be evaluated. Objectives of this study were to: 1) evaluate the impact of alternative land surface disturbance strategies, high-intensity winter-grazing (WG) and wildfire (WF), compared to a commonly used summer-long continuous grazing (CG), on the soil microbial community, measured by total soil microbial biomass, percent soil microbial functional groups, and soil microbial diversity and 2) determine the impact of the land surface disturbance strategies on soil moisture and temperature, infiltration rates, and erosion processes, which include soil loss, surface runoff, and sediment yield. To determine changes in the soil microbial community, four soil cores were taken from nine exclosures (3 CG, 3 WG, and 3 WF) during the beginning of the growing season (June) and peak growing season (August) for two years (2017 and 2018). Soil moisture and temperature sensors were installed at three depths (6-, 12, and 24-inch), across replicates of nine land surface disturbance areas (3 CG, 3 WG, and 3WF pastures), and monitored for approximately two years (April 13th, 2017 to December 31st, 2018). Infiltration tests were also performed within each land surface disturbance area every two months from June 2017 to August 2018. Surface runoff, soil loss, and sediment yield were modeled using the Watershed Erosion Prediction Project (WEPP) model. A total of nine scenarios were developed to evaluate the impact of land surface disturbances individually, hillslope individually, and the combined impact of land surface disturbance and hillslope. Total soil microbial biomass was significantly affected by land surface disturbances but was dependent on vegetation characteristics. Total microbial biomass increased as a result of fire in areas that had a greater percentage of shortgrass species and decreased in areas that had more mid-grass species. Similar to total microbial biomass, the effect of the surface disturbances on microbial functional groups was dependent on vegetation characteristics and differed between land surface disturbance treatments. No differences were found for soil microbial diversity between land surface disturbance treatments. Soil moisture and temperature were affected by land surface disturbance treatments, while infiltration rates were not. Although there were differences between land surface disturbance treatments for soil moisture and temperature, these differences are not likely to have any biological effect with the greatest difference between treatments being 0.9 °C. Results from the WEPP model showed that wintergrazed land surface disturbance scenarios do not drastically increase the amount of surface runoff, soil loss, or sediment yield when compared to continuous summer-long grazing while wildfire has dramatic increases compared to summer-long continuous grazing. Results of this study show that high-intensity winter-grazing does not cause detrimental impacts on the soil microbial community or soil hydrological processes. However, wildfire may not cause detrimental impacts on the soil microbial community but does increase surface runoff, soil loss, and sediment yield. This suggests that highintensity winter-grazing could serve as a sustainable land surface disturbance strategy.

Library of Congress Subject Headings

Soil microbial ecology -- Great Plains.
Grazing -- Environmental aspects -- Great Plains.
Soils -- Effect of fires on -- Great Plains.
Rangeland hydrology.

Format

application/pdf

Number of Pages

101

Publisher

South Dakota State University

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Rights Statement

In Copyright