A Web-Based Program for Predicting Soil Organic Matter and Phosphorus Changes from Applications of Manure and Compost.

Application of large amounts of manure and compost can cause excess P in soils. This fact is not always clearly understood by producers, especially organic producers who use compost applications to supply most of the nutrients for their crops. Because compost releases nutrients slowly, most users of compost and most information sources about rates of compost to apply, assume that it is impossible to apply excess amounts of compost. Overapplication of compost increases farmers’ input costs and can pollute ground and surface water with P and nitrate. To help farmers to better manage their compost and manure applications, we developed a web-based program to predict soil P and OM changes with time for various rates of manure and compost applications. The predictions are based on published papers that describe the relationships between soil P and OM accumulation with various organic amendments. The program has three major sections: user inputs, model parameter determination, and prediction output. A discussion of possible extension of the program to predict excess N mineralization from compost applications also will be discussed.