Managing Phosphorus in Beef Feeding Operations

A commercial feedlot study was conducted to determine manure nutrient flow in six feedlots representing 6,366 cattle. On average, cattle involved in this summary were yearlings (BW = 353 kg) and gained 183 kg over 123 d. It was calculated that 11.5% of the feed nitrogen and 16.9% of the feed phosphorus was retained by the animal with the remaining nutrients excreted. On average, 25.6 kg of N and 4.1 kg of P (DM basis) were excreted per fed beef animal. On average, 887 kg total manure (solids and water) were removed per finished animal (7.2 kg/animal/d) averaging 73% total solids. Approximately 28% of the total solids are volatile solids with a wide range of observed volatile solids levels (9 to 63%). Based upon these data, 30.7% of the excreted nitrogen or (7.8 kg/animal fed) and 90.2% of the excreted phosphorus (or 3.7 kg/animal fed) were removed in manure at cleaning. These data suggest there is variation in the amount of P harvested from beef feedlots, reflecting the variation between feedlots as a result of individual pen conditions, and requirements for use and handling of the manure in the pen prior to harvesting. These data suggest that estimates based on the references (ASAE, 2000; USDA, 1992) of P removed in manure are too high, and indicate that acres required for distribution of manure P in NMPs should be 50% of the acres predicted by those references