Because of the unusually warm winter, many people who applied anhydrous ammonia last fall are concerned they might have lost some of their nitrogen, according to University of Illinois assistant professor of crop sciences Fabian Fernandez.

"Nitrogen transformations and losses depend on many variables and complex interactions," said Fernandez, "including soil temperature, time of fall-nitrogen application, use of a nitrification inhibitor, rate of biological activity, drainage, amount and frequency of rain, and soil type."

Fernandez says that it is first necessary to estimate how much of the applied nitrogen has been transformed to nitrate.

"When anhydrous ammonia is applied, it reacts with soil water to convert to ammonium," he explained. "In this form, nitrogen is held by the soil and cannot be leached out of the root zone or denitrified. However, once ammonium transforms to nitrate, it can be leached out with rainwater moving through the soil profile or denitrified when soils are warm and saturated with water."

The bacteria that mediate nitrification are most active at warm temperatures (above 50 degrees F) when the soil is not saturated with water. When the soil temperature is below 32 degrees, nitrification does not occur.

Daily minimum soil temperatures at four inches below the soil surface ranged from 35.7 to 45 degrees F in Champaign during January and February. "The fact that temperatures never reached 32 degrees suggests that nitrifying bacteria have remained active most of the fall and winter," said Fernandez.

Champaign soil temperatures were also relatively constant last winter, with average daily fluctuations of 2.2 degrees F when minimum soil temperatures in the field were below 39 degrees. These conditions would not produce a substantial lag in bacterial activity from day to day. Fernandez said that similar conditions existed in other parts of Illinois.