2008 Year in Review

From the Fields

Fall application of nitrogen is a common practice in northern Illinois. What are some factors associated with fall application of this nutrient for the 2009 corn crop?

First, consider the economic optimum rate of nitrogen. See the nitrogen rate calculator at Corn Nitrogen Rate Calculator. Select northern, central, or southern Illinois in addition to the price of corn and cost of nitrogen.

Soil type, climatic condition, and form of nitrogen fertilizer have a great impact on the amount of loss that may occur over winter. Nitrogen in the nitrate form is susceptible to loss by leaching and by denitrification.

Fall application of nitrogen should be avoided on coarse-textured, sandy soils or shallow soils over fractured bedrock. These offer the greatest possibility for leaching.

Farmers planning fall nitrogen application are advised to avoid using nitrate-containing fertilizers (ammonium nitrate or UAN). Also, urea should not be applied in the winter. Since it converts to nitrate more slowly than other nitrogen sources, anhydrous ammonia is the preferred form to use.

Anhydrous ammonia should not be applied until the soil temperature at the 4-inch level is below 50 degrees F. If a nitrification inhibitor is used with anhydrous ammonia, the nitrogen can be applied earlier, when the soil temperature at the 4-inch depth reaches 60 degrees F. Soil temperatures must be below these levels and continuing to get colder. At these temperatures, soil organisms are less active and less likely to convert ammonium to nitrate. Below 50 degrees F, nitrification slows rapidly, but it does continue until 32 degrees F. These temperature guidelines also apply to injected liquid manure with high ammonium nitrogen content.

Delay fall anhydrous ammonium application irrespective of soil temperature until at least the third week of October in northern Illinois.

Soil thermometers should be used to guide the fall application as average dates on which the above-mentioned temperatures are reached are not satisfactory because of year-to-year variation. Current soil temperature is available at several web sites, one being Soil Temperatures.

If using ammonium sulfate, delay application until soil temperatures have fallen below 50 degrees and do not apply before the first week of November in the northern three tiers of counties.

Nitrification inhibitors can be viewed as a nitrogen management tool. They will increase the cost of fall application, but could significantly improve the efficiency of fall-applied nitrogen.

Further information on nitrogen management can be found in the current Illinois Agronomy Handbook, available at Extension offices and on-line at Illinois Agronomy Handbook.

by  Editor, theCity1.com
October 5, 2008