Identifying challenges and opportunities for improved nutrient management through U.S.D.A's Dairy Agroecosystem Working Group

Nutrient management is a priority of U.S. dairy farms, although specific concerns vary across regions and management systems. To elucidate challenges and opportunities to improving nutrient use efficiencies, the USDA’s Dairy Agroecosystems Working Group investigated 10 case studies of confinement (including open lots and free stall housing) and grazing operations in the seven major U.S. dairy producing states. Simulation modeling was carried out using the Integrated Farm Systems Model over 25 years of historic weather data. Dairies with a preference for importing feed and exporting manure, common for simulated dry lot dairies of the arid west, had lower nutrient use efficiencies at the farm gate than freestall and tie-stall dairies in humid climates. Phosphorus (P) use efficiencies ranged from 33 to 82% of imported P, while N use efficiencies were 25 to 50% of imported N. When viewed from a P budgeting perspective, environmental losses of P were generally negligible, especially from dry lot dairies. Opportunities for greater P use efficiency reside primarily in increasing on-farm feed production and reducing excess P in diets. In contrast with P, environmental losses of nitrogen (N) were 50 to 75% of annual farm N inputs. For dry lot dairies, the greatest potential for N conservation is associated with ammonia (NH3) control from housing, whereas for freestall and tie-stall operations, N conservation opportunities vary with soil and manure management system. Given that fertilizer expenses are equivalent to 2 to 6% of annual farm profits, cost incentives do exist to improve nutrient use efficiencies. However, augmenting on-farm feed production represents an even greater opportunity, especially on large operations with high animal unit densities

Enzymatic Quantification of Phytate in Animal Manure

Phytate (inositol hexaphosphate) has been identified as a major organic phosphorus (P) form in soil, animal manure, and other environmental samples. Although a number of methods are available for quantitative isolation and determination of phytate, they are time-consuming and not amenable to routine analysis. We developed a simple, rapid method for enzymatic determination of phytate in animal manure. Animal manure was extracted by H2O, 1M hydrochloric acid (HCl), 0.1M sodium acetate (NaOAc, pH5.0) with or without 0.05M ethylenediaminetetraacetate (EDTA), and 0.25M or 0.5M sodium hydroxide (NaOH)–0.05M EDTA. Extracts were diluted (1/10–1/150) and adjusted to pH5.0 in sodium acetate buffer. The diluted extracts were then incubated at 37 °C for 1 h in the absence and presence of fungal 3-phytase (PHY) and potato acid phosphatase (PAP). Enzymatic hydrolyzable organic P was calculated as the difference in inorganic P (Pi) between the mixtures with and without enzymes. Our data indicated that enzymatic incubation of properly diluted and pH-adjusted HCl or NaOH/EDTA extracts released phytate P. The complementary substrate specificity of the two enzymes is considered to enhance the effectiveness of enzymatic hydrolysis. Consequently, we recommend this method of combining PAP and PHY for quantifying phytate P. Additional research is being conducted to verify the effectiveness of this method for general use across a wider range of soils and manures