Soil microorganisms respond distinctively to adaptive multi-paddock and conventional grazing in the southeastern United States

Authors: WHITE, LAURA - Former ARS Employee; Yeater, Kathleen; Lehman, R - Michael

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2023
Publication Date: 7/11/2023
Citation: White, L.J., Yeater, K.M., Lehman, R.M. 2023. Soil microorganisms respond distinctively to adaptive multi-paddock and conventional grazing in the southeastern United States. Soil Science Society of America Journal. 87:1096–1108. https://doi.org/10.1002/saj2.20573.
DOI: https://doi.org/10.1002/saj2.20573

Interpretive Summary: Grasslands occupy about 40% of the earth’s land, sustaining domestic livestock and wildlife, and providing a variety of ecosystem services. Some grazing practices may degrade grassland soils and reduce their capacity to sustain their valuable functions and services such as soil C sequestration. Because soil microorganisms are an inherent component of healthy grassland soil, we measured the response of soil microbiological properties to conventional and adaptive multi-paddock (AMP) grazing management practices at multiple locations in the southeast U.S. We found higher amounts of soil microbial biomass and greater carbon and nutrient cycling activities in grassland soils under AMP grazing management compared to conventional management. In contrast, carbon limitation of respiratory activities was higher in the conventional ranches compared to AMP ranches indicating decreased processing of soil C and formation of microbial biomass which are key processes leading to stable soil carbon. A large and active soil microbial community observed under AMP grazing management should maintain access to nutrients for plants and stimulate stable soil organic matter formation. In summary, we found grazing management influenced the numbers and key activities of soil microbes that may increase retention of C and nutrients in these grassland systems and sustain grassland function.

Technical Abstract: Variable reports regarding the effects of grazing management on soil properties in grasslands suggest the need for further study. We measured the response of soil microbiological properties to conventional and adaptive multi-paddock (AMP) grazing management practices at five locations arranged in a north-south transect from southern Kentucky to Southern Mississippi. Six sampling transects were established at each ranch and three composite soil samples were collected along each transect. We measured total DNA as a proxy for soil microbial biomass, abundance of taxonomic groups by quantitative PCR (qPCR), potential nutrient cycling activities by qPCR of functional genes, and potential carbon (C) mineralization activities. Numbers of fungi (p<0.0001) and bacteria (p<0.0001) were higher under AMP management compared to conventional management; however, there was no difference in the fungal:bacterial ratios between the two management treatments. Changes in relative abundance of several taxa indicated management-induced changes in soil microbial structure. The numbers of gene copies encoding for nitrification, denitrification, and phosphate hydrolysis were significantly higher in AMP ranches compared to the conventional ranches. Basal soil respiration was elevated (p< 0.0001) in AMP ranches compared to conventional ranches presumably due to the higher numbers of microbes that were actively transforming plant exudates and residues. In contrast, carbon limitation of respiratory activities was higher (p< 0.0001) in the conventional ranches compared to AMP ranches indicating decreased processing of soil C and formation of microbial biomass which are key processes leading to stable soil carbon. In summary, we found grazing management influenced the numbers and key activities of soil microbes that may increase retention of C and nutrients in these grassland systems.