The Nitrogen Decision Aid is a computerized program that predicts the amount of N mineralized from planting to side-dress or 5-leaf growth-stage. By applying just enough N-fertilizer to reach the critical soil nitrate concentration it is possible reduce this waste. This model is designed for Northern climates that will have some frost in the soil during the winter. Each Year more than 10 billion kg of nitrogen fertilizer are applied to croplands in the United States at a cost of more that $3.5 billion (USDA Economics and Statistics System, 1998). It is estimated that the efficiency of this applied nitrogen (N) ranges from about 30% to about 70% (Pilbeam, 1998); thus, large amounts of fertilizer N are lost or wasted each year. The Nitrogen Decision Aid is a computerized program that predicts the amount of N mineralized from planting to side-dress or 5-leaf growth-stage. By applying just enough N-fertilizer to reach the critical soil nitrate concentration it is possible reduce this waste. This model is designed for Northern climates that will have some frost in the soil during the winter.