The decision on applying late season N on corn involves 3 questions: 1) Does the crop need it? 2) Do only certain sections of the field need it? 3) How much do I apply to those sections that need it? An aerial photograph of the corn field (taken between the period of full canopy to tasselling) is an excellent tool to determine the answers to these questions. If the aerial view isn't splotchy with several shades of green, then the field probably has enough N, and you'll save money by not applying N.

Fig. 1. A pivot-irrigated field that would benefit from fertigating different amounts of N through the pivot to different portions of the field and units of N each segment needs.

If N is to be applied, treat only those areas that are off color. An off-the-shelf computer program (Adobe PhotoShop) is used to analyze the "green-ness" of weaker spots in the field and compare them to those dark green spots where N is adequate. Procedures are found on-line at: Agr J (http://agron.scijournals.org/cgi/content/full/94/3/397).