Date of Graduation


Document Type


Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level



Crop, Soil & Environmental Sciences


Mary Savin

Committee Member

Dirk Philipp

Second Committee Member

Kenneth Coffey

Third Committee Member

Trenton Roberts

Fourth Committee Member

Amanda Ashworth




Hippuric acid is a breakdown product of tannins, which bind with proteins in the animal rumen and slow down protein metabolism, thus increasing nitrogen (N) retention in the animal. Increased hippuric acid concentration in bovine and ovine urine applied to soil may decrease rates of nitrification, denitrification, and nitrous oxide fluxes in pasture soils. Additionally, condensed tannins have increased rates of carbon mineralization when incorporated in humus and leaf litter. To evaluate effects of hippuric acid concentration, treatments of urine from sheep fed a tannin-supplemented diet, synthetic urine, or urea controls were applied to intact soil cores seeded with crabgrass (Digitaria ciliaris (Retz.) Koeler) and maintained in a greenhouse. Ammonia volatilization was estimated using indicator probes for 19 days. Leachate was collected with micro-lysimeters at four depths over 86 days for analysis of nitrate-N and ammonium-N. Soil samples were collected after 28 days from three depth intervals and analyzed for nitrate-N, ammonium-N, total N and carbon, organic matter, particulate organic matter, and Mehlich-3 extractable nutrients. Ammonia volatilization and ammonium-N concentrations were greatest immediately following treatment application but were not different in relation to hippuric acid concentration (P < 0.05). Nitrate-N concentration in leachate did not vary among urine treatments, but a reduction was observed in the urea control with hippuric acid compared to the urea-only control. Nitrate-N and ammonium-N concentrations in soil varied primarily by depth but were not different in relation to hippuric acid content. Organic matter, particulate organic matter, and total soil carbon were not affected by treatment, but all decreased with increasing depth. Results indicated that manipulation of hippuric acid concentration of ruminant urine is not an effective tool to increase N retention or carbon sequestration in pasture systems.

Available for download on Saturday, August 30, 2025

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