The University of Illinois is undertaking a project to identify and map current soil nitrogen levels throughout the state. A great deal of nitrogen from both fertilizer and mineralization of soil organic matter remains in Illinois soils due to the low corn yields and the early death of the crop in dry areas. University of Illinois crop sciences professor Emerson Nafziger says that nearly all of the residual nitrogen is in the form of nitrate.


From an economic and environmental standpoint, it is important to know how much soil nitrogen remains in fields. “We are initiating a project to sample soils for nitrogen this fall,” Nafziger says. “Funding is being provided by the Council for Best Management Practices, so there will be no cost to producers and others who take samples.”

Unlike ammonium, nitrate moves readily in the soil. With no roots to take it up, the nitrate in the soil is likely to move downward with water. If the weather remains relatively dry between now and next spring, some nitrate may remain in the soil to be available for next year’s crop.

If there is enough rainfall to get tile lines to run, some of the nitrate will leave the field in drainage water or migrate below the root zone, according to Nafziger. In fields without tile drainage, wet soil and soil temperatures above 50˚F can cause nitrate to be converted to nitrous oxide or nitrogen gas, both of which will leave the soil.

Knowing how much nitrate is present this fall can make it easier to estimate how much might be there next spring, although the actual amount depends mostly on conditions over the winter. Nafziger says all soil nitrogen levels provide an indication of whether it is worth looking at soil nitrogen levels in the spring. Knowing fall nitrate levels helps producers to evaluate the chances of being able to fine-tune nitrogen rates if crop farmers follow corn with corn.

Nafziger’s plan is to post soil nitrogen values on a map and make it available on a Web site without identifying fields or producers.

Those interested in participating in this project can contact Nafziger at ednaf@illinois.edu.