Tuesday, November 6, 2007 - 9:50 AM
153-2

A New Approach to Formulating N Rate Guidelines for Corn.

Emerson D. Nafziger, University of Illinois, 1102 South Goodwin, Urbana, IL 61801 and John E. Sawyer, Agronomy, Iowa State University, Ames, IA 50011.

Until recently, N rate recommendations for corn (Zea mays L.) differed among U.S. Corn Belt states, including states with similar soils where such differences would not be expected. Many of these recommendation systems were based on state-specific data, some of it several decades old. Some recommendation systems required determination of expected yield, which was usually based on historical yield. Recommended N rates were then calculated as a function of expected yield, in some cases with adjustments based on soil characteristics. Some models included the option to improve economic returns as corn and N prices changed, but such adjustments were often inadequate when N prices increased rapidly, or were simply not made. Base N rate recommendations were often for corn following corn, with adjustments to the N rate when soybean or another legume preceded corn. Recent N response data, especially those from trials with high corn yields, have shown that N rate recommendations calculated based on actual, as opposed to expected, yields are often higher than observed optimal N rates. And, particularly when corn follows soybean, the correlation between the predicted optimum N rate and the corn yield at that N rate is often very weak. In an attempt to utilize more current N response data and to include economic maximization more directly, we worked with other scientists to devise a method to combine data from response trials into a web-based N rate calculator. This calculator allows input of corn and N prices, and calculates N rate ranges that are expected to produce maximum economic returns to N. Such N rate guidelines can be calculated for any of several states, and for corn following corn as well as for corn following soybean. Advantages and drawbacks to this approach will be discussed.