Precision farming studies are revealing that substantial amounts of fertilizer nitrogen (N) often are lost soon after application. In a surprising number of fields, most of the fertilizer N is lost before it is needed by the crop. Figure 1 (right) shows aerial photographs from a portion of such a field. This field received 125 lb of N/acre as anhydrous ammonia in the fall of 1997. The late spring test indicated that soil nitrate concentrations were less than 10 ppm at the end of May 1998. The aerial photograph (top) taken in early July showed streaks of light-and-dark green plants. The streaks were caused by nonuniform applications of anhydrous ammonia between knives. Most of the plants in the field, however, had run out of N when they needed it most.