Panel Discussion: Field Experience with Nitrogen Applications for Individual Corn Fields.

(Nester) In the Western Lake Erie Basin, we have conducted numerous in-field replicated nitrogen plots for five years. This effort has been aimed at helping farmers discover a more precise nitrogen rate for their farms, under their management program, as opposed to a one-size-fits-all nitrogen rate. The lime, P and K on these plot field have been precision managed by zones, some based on soil type and some based on yield variation. Our experience with these replicated plots has shown that the optimum nitrogen rate is not related to the yield goal of the field or zone. Somewhat related to soil type, the optimum rate will vary with cost of nitrogen and selling price of the grain, but the recovery rate of the system used is the most important factor. We have found high yielding areas of fields have maximum yield at lower N rates, while marginal production areas have responded to higher rates of N.  Root restriction, compaction, shallow topsoil, and denitrification are all characteristics that require more nitrogen in the low yielding soils. We have also found that excess nitrogen above optimal rates, not only increases costs, but often reduces yield. Nearly all participants in our plot program have found they were over-applying nitrogen. These farmers have cut their rates 15 to 25% after participating in the plot program. Eventually the proper way to optimally manage nitrogen in variable soils will be with variable rate nitrogen, but much work needs to be done to find the right rate. (Schaefer) With the high cost of crop inputs and the high stakes of crop production farmers today are now intensively managing their crops. Many producers are using the IPNI’s 4 R’s of nutrient stewardship (Right Source, Right Rate, Right Time, and Right Place) as a base for their nitrogen application system. An increase of 6 bu/a/yr in corn is needed to produce an average yield of 300 bu/a by the year 2030. To do this growers will need to carefully manage all plant nutrients, both macronutrients and micronutrients, to maximize yield. Since 2008 in central Illinois we have seen an increase in multiple applications of nitrogen with a portion of the total nitrogen applied preplant with smaller increments applied at planting, and in some fields an application made to the growing corn crop. This spoon feeding or split application of nitrogen has been shown to increase yields by 17-20 bu per acre with an economical advantage to the grower of as much as $75.00 per acre. In central Illinois we use the N-Rate calculator to estimate what that nitrogen budget should be. By following a split application program for nitrogen management the grower can maximize production, optimize nutrients and minimize environmental impact.