With nitrogen prices hovering around $0.80 per unit, deciding when and how much to apply is becoming increasingly difficult. Below are some tips to help make the most of your nitrogen program.
Do not skip the starter. Research has shown the benefits of applying 20-30 pounds of N at planting. Starter should even be considered on manured fields. Cold soil temperatures early in the season prevent the mineralization of N from organic forms. A corn crop that starts behind due to lack of N is not likely to maximize yield at the end of the season.
Split applications of N into as many passes as feasible. The more frequently N is applied, the more efficiently it can be used. Explore late season options for application. A corn crop takes of 60-70% of its N requirement by tasseling. If 70% of the N is applied between starter and sidedress, any additional applications can be fine tuned based on the performance of the crop at that time.
Soil test for N (both nitrate and ammonium), even on non-manured fields. Using a PSNT to adjust sidedress rates is common practice but using soil tests later in the season to evaluate a nitrogen program is less common because there is no clear interpretation of the results. However, this data especially in the hands of a trained crop advisor, can be a useful piece of the puzzle that is N management.
Use tissue tests to help fine tune an appropriate late season application rate or possibly determine if the application is needed at all. Collecting tissue samples 2 to 4 times during early growing season can help to monitor how efficiently the crop is utilizing the N that has already applied. If N was applied at a rate assuming an average growing season and yield, but conditions are favorable for a higher yield, a tissue test can help determine if a higher rate of N is needed to produce that higher yield.
Most importantly chose an appropriate yield goal based on the history of the field. Applying additional N to a field that has other limitations such as drainage problems or low fertility will likely result in financial loss. Also remember that maximizing yield does not mean maximizing profitability. To help fine tune an appropriate N rate for your area and N prices, use the Maximum Return to Nitrogen calculator available at http://cnrc.agron.iastate.edu/.