In this era of high fertilizer prices and environmental concerns, we have to know where our crop nutrients are coming from and where they are going. The "big three" of corn and soybean production are Nitrogen (N), Phosphorus (P) and Potassium (K). Of these, Nitrogen is of special concern because it can be transferred throughout the soil profile by water. This means that it can be readily moved into ground water and can cause some pollution problems as well as not being available for the growing crop. Both P and K become fixated in the soil upon application and generally are not considered a pollution threat unless the soil physically moves through erosion to bodies of water.