Simulation to evaluate dairy manure systems

An existing dairy forage system model (DAFOSYM) was expanded to include submodels for manure production, collection, storage, and application to crop land. The original DAFOSYM simulated the growth, harvest, storage, and utilization of alfalfa and corn on a dairy farm over 25 years of weather. The revision allowed simulation of the quantity and nutrient content of manure produced as a function of feed composition and consumption, milk production, and animal growth. Nutrient losses in manure handling, storage, and application were subtracted to determine nutrients available for crop growth. The facilities, machinery, labor, and fuel required were modeled to determine the costs of manure handling. The integrated model provided a tool for evaluating and comparing the long- term performance and economics of alternative manure systems for dairy farms and their interaction with feed production. Manure systems using long-term storage with spreading, injection, or irrigation have greater direct costs to the farmer than the daily haul system commonly used in the upper midwest. If long-term storage systems are required to protect the environment, the annual net cost of manure handling will increase up to $651 cow for small (60 cow) and $451 cow for large (250 cow) dairy farms.