C. Alan Rotz and Michael S. Corson. USDA-ARS, Building 3702, Curtin Road, University Park, PA 16802-3702
Grasslands, like other agricultural components, are managed at the farm scale. Management changes that affect grass production and use also affect other farm components and vice versa, which ultimately affect farm performance and profitability. To evaluate the management of grassland systems, a comprehensive and integrated evaluation is required that includes the effects and interactions of all major farm components. These potentially include the production of other crops on the farm; harvest, storage and feeding of conserved feeds; animal intake and production; manure production and nutrient cycling; crop establishment and maintenance; and the combined influence of these components on the costs and returns of the farm. Whole-farm simulation provides an important tool for integrating these components. Only a few models have been developed at this scale; one of those is the Integrated Farm System Model. Growth of grass, alfalfa, corn, soybean, and small grain crops are simulated over many years of weather along with the operations of tillage, planting, harvest, storage, and feeding to predict resource use, timeliness of operations, crop losses, and nutritive changes in feeds. The production of dairy or beef animals is related to the nutritive value of available feeds, and nutrient flows through the farm predict potential nutrient accumulation and loss to the environment. Simulated performance is used to determine production costs, income, and farm net return. Recent development has focused on modeling the dynamics of multiple species in a pasture including cool and warm season grasses, legumes, and forbs. Farm scale simulation provides a useful tool for research and education. Although there has long been an interest in using this type of tool in farm management, model complexity has deterred this application.