Because of the rising price of nitrogen (N) fertilizer, university personnel across the country are in the process of fine tuning N recommendations for com. Historically, each state has had different N recommendations based on research results obtained in different production systems and growing environments across each state. Some states in the Com Belt have used a yield potential (yield goal) approach to N recommendations. The expected yield is multiplied by a factor (usually 1.2) and then N credits for previous crop, manure, etc. are subtracted. One problem with this method is that as com yields increase N recommendations also increase. While this might seem logical, some studies show that N requirements are rising at a much slower pace than com yield. This simply means the com plant is becoming a more efficient user of N. States using the yield goal approach are realizing that, with time, their recommendations are increasingly exceeding the needs of the crop. For this reason, they are considering alternatives to the yield goal approach.
Grove, John H. and Schwab, Gregory J., "The Corn Belt Multi-State Corn Nitrogen Rate Calculator: Not Reliable for Kentucky Corn Producers" (2006). Soil Science News and Views. 183.