EFFECT OF SMOOTH BROMEGRASS MANAGEMENT ON GRAZING CATTLE DUNG DECOMPOSITION, CO\u3csub\u3e2\u3c/sub\u3e FLUX, AND SOIL NUTRIENT MOVEMENT

Rapid nutrient cycling improves forage quality and livestock production in pastures. Interseeding legumes may be a strategy to enhance N cycling, but effects of dung excreted from cattle grazing pastures with legumes on dung decomposition rates and soil N cycling have not been studied. Our objective was to evaluate how dung excreted from cattle grazing legume-interseeded, N-fertilized, and unfertilized smooth bromegrass (Bromus inermis Leyss.) pastures affects dung chemical composition, dry matter decomposition, CO­2 flux, and N availability in soil. Freshly deposited dung from yearling steers grazing legume-interseeded, N-fertilized, and unfertilized pastures was collected and placed as pats in a neighboring pasture where experiments were established to evaluate effects of year (2014 and 2015), season (June and August), cattle diet, and time after dung placement (3, 7, and 30 days) on dung [dry matter, C, N, water extractable C (WEC), and water extractable N (WEN) contents] and soil (WEC, WEN, NH4-N, and NO3-N) characteristics. Across the experiments, these characteristics were often found to depend on year, season, and diet interactions, but overall, dung from legume-interseeded pastures had greater N content, WEC, and WEN, and lower C:N ratio than dung from N-fertilized and unfertilized pastures. Dung from legume-interseeded pastures also decomposed faster and had more CO2 flux than dung from unfertilized pastures, but showed no differences with that from N-fertilized pastures. Soil nutrient movement was not affected by cattle diet, but may have been limited by the time of dung placement and the depth of soil analyzed. Legume interseeding distinguish itself as a positive component of pasture management with an improved potential for dung decomposition and soil nutrient movement because of nutrient rich dung. Advisors: John A. Guretzky and Walter H. Schach