Degree

Doctor of Philosophy (PhD)

Department

School of Plant, Environmental, and Soil Sciences

Document Type

Dissertation

Abstract

Utilizing winter annuals in livestock pastures reduces feed costs of hay, and provides additional vegetative cover that is beneficial to the soil. However, how this practice affects the soil microbial communities has not been well studied. Two sites were included in this study. Both were commercial cattle grazing operations that over-seeded a mixture of grasses, legumes, and brassicas into pastures dominated by bahiagrass (Paspalum notatum). Soil health was assessed using a suite of physical, chemical, and biological properties. Soil physical assessments included bulk density and aggregate stability. Soil chemical assessments included macronutrients, pH, soil organic matter (SOM), total carbon (TC), and total nitrogen (TN). Fatty acid methyl ester analysis and enzyme assays were used to determine soil microbial community structure and activity. The objective for site one was to determine how soil health changed with time along a topographic sequence. The objective at site two was to compare the soil health of pastures using varying years of winter annuals and grazing. At both sites, TC and TN did not change with date of sampling although SOM did increase by 6% in site one. Nitrate concentrations decreased by 82% within two years at site one and remained consistent at 2.15 mg kg-1 at site two. Potential soil microbial enzyme activity increased with increasing years of management (grazing and winter annuals) by 27% and over time by 32% at site one and an average of 70% at site two. Total microbial abundance did not change over time at either site. Soil microbial community structure responded to abiotic conditions (e.g. season and topography) but not to years of management. This pasture management technique of over-seeding a diverse mix of winter annuals may, with time, allow for a steady state of C and N while SOM increases and inorganic nitrogen decreases, and enhance the total soil microbial community and their potential enzyme activity.

Date

10-24-2018

Committee Chair

Fultz, Lisa

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