Achieving Environmental Balance of Nutrient Flow Through Animal Production Systems

An animal nutrition-based model to predict nutrient excretion to be managed on food animal production units is recommended. In a dairy model, average yearly excretions per high-producing cow of common fertilizer nutrients were estimated at approximately 250 lbs N, 461bs P, 100 lbs K, and 80 lbs Ca. Multiple cropping systems have the potential to consume about 400 lbs N/acre and 50 lbs P/acre. Applicable data of this nature for specific farms are essential for development of nutrient accountability budgets. Separating fibrous solids from flushed manure facilitates irrigation of the effluent in many manure management systems but removes relatively few nutrients which are of environmental concern (e.g., N and P) because they are mostly soluble and remain with the effluent. Stationary screens are most commonly used but settling basins that can be cleaned with wheel tractors with front-end loaders are gaining favor as improved designs are tested. Estimated flow of N and P through several types of manure management systems show a wide range in the predicted acreage needed to achieve environmental balance. More input into these budgets by agronomists and soil scientists is needed; however, the trends are well founded and show that more acres are required when P is selected as the primary nutrient in acreage budgeting for manure disposal than when N is selected. Many soils are deficient in P so that some allowance may be possible for N criteria to be used until soil tests show that soil P reserves or groundwater levels of P are excessive. Manure management should be permitted to vary depending on differences in soil types and feeding practices on individual farms without automatically limiting farms to manure application rates appropriate for higher than actual manure excretion levels of N and P or less intensive cropping. Groundwater sampling wells on farms and regular soil sampling are also important to establish and maintain a history of environmental responsibility associated with the cropping and manure management programs.