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Yellowstone National Park is home to the largest population of free ranging genetically pure American bison (Bison bison). The current population estimate is 4,800 animals which utilize the parks grasslands throughout most of the year. In 2015, the National Park Service began an assessment of the effects of bison across the migratory range of both the Central and Northern Range herds and we present here a set of experiments conducted at a subset of 23 field sites across the altitudinal migratory gradient. The effects of bison a population this size on grassland ecosystems has not been determined and in this study we present the contributions of plant available nutrients returned to soil by bison dung and urine using natural and experimental applications of animal wastes. In all experiments we quantified KCl extractable pool sizes of soil ammonium, nitrate and phosphate using either soil cores or ion exchange membranes (IEM). At 5 sites in the northern range we applied simulated bovine urine and quantified N and P mineralization using ion exchange membranes for 40 days. At 2 sites we observed bison urination and collected soil cores for 3 weeks after deposition. At 12 sites we quantified the pool sizes of N and P in dung of varying ages and at 2 sites we homogenized fresh bison dung and reapplied dung pats to the soil surface and quantified pool sizes with IEMs for 10 days. IEMs unlike soil cores allow for the continuous trapping of mineralized N and P pools and our data shows that dung provides significant amounts of N and P while urine provides only N. The combined contribution of dung and urine to N and P soil pools represents a significant fertilizer effect ranging from 15-36 kg N/Ha and 3.5-7.1 kg P/Ha.