A single model is used in EPIC for simulating all the crops
considered (Corn, Grain sorghum, Wheat, Barley, Oats, Sunflower,
Soybean, Altalfa, Cotton, Peanuts, Potatoes, Durham wheat. Winter
peas, Faba beans, Rapeseed, Sugarcane, Sorghum hay. Range grass.
Rice, Casava, Lentils, and Pine trees). Of course, each crop has
unique values for the model parameters. EPIC is capable of
simulating growth for both annual and perennial crops. Annual
crops grow from planting date to harvest date or until the
accumulated heat units equal the potential heat units for the
crop. Perennial crops maintain their root systems throughout the
year, although they may become dormant after frost. They start
growing when the average daily air temperature exceeds their base
temperature.
Phenological development of the crop is based on daily heat unit
accumulation. It is computed by using the equation