The low corn price for Y2K combined with the recent increases in fertilizer nitrogen prices have caused agronomists, suppliers, and farmers to closely examine the amount of N they will apply this spring. Corn yield variations and differences in yield response to nitrogen fertilizer are primarily a function of the soil characteristics (depth, drainage, organic matter content, and yield potential) of the environment in which the corn is grown. The response to fertilizer N is also influenced by the amount of available nitrogen from other sources such as residual nitrate-N in the root zone or nitrogen from legumes or manure. These factors are accounted for by the UW soil test recommendations for nitrogen and the recommended adjustments. The combination of these components allows for the estimation of the economically optimum N rate. The very best rate of N to apply is the economic optimum rate because the last unit of N added just pays for itself with additional yield. This rate maximizes the dollar return per acre to the farmer.