2005 Year in Review

From the Fields

Source: Jim Morrison, Extension Educator, Crop Systems, Rockford Extension Center, University of Illinois, Phone 815-397-7714, FAX 815-397-8620, Email morrison@uiuc.edu

Fall application of nitrogen is a common agronomic practice in northern Illinois. Let’s look at some of the factors associated with application of this nutrient in the fall for the 2006 corn crop.

The 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, or the movement of nitrate nitrogen in soil solution below the root zone. Nitrate is also subject to loss by denitrification, the conversion of nitrate nitrogen to unavailable atmospheric nitrogen.

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

Farmers planning fall nitrogen application are advised to use the ammonium form and avoid using nitrate-containing fertilizers. 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 3 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.

If applying anhydrous ammonia or injecting liquid manure in the fall, wait until soils are cold enough. Further information on nitrogen management can be found in the current Illinois Agronomy Handbook, available at Extension offices and on-line at The Agronomy Handbook

by  Editor, theCity1.com
October 15, 2005