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Nitrogen monitoring should help Illinois growers in their estimates
Illinois Correspondent

URBANA, Ill. — In the wake of “Superdrought” 2012, many producers throughout the Midwest are eyeing their fields for soil nitrogen needs in the new year. This is behind Emerson Nafziger’s Illinois Soil Nitrogen Monitoring project, to determine how much nitrogen is in the soil now as a means of estimating likely loss through this winter and early next spring.

“There’s a lot of interest in it,” Nafziger, crop sciences professor at the University of Illinois, noted on Jan. 8 about the first results of the project to sample soil in late fall, to see how the dry growing season and low corn yields affected nitrogen levels.

“Always before when we’ve had a drought year like 2012, there’s probably quite a bit of nitrogen left in the soil. But, that’s about as far as it’s gone. This (project) is the first attempt, at least over a range of sites like this, mostly on farmers’ fields, to see how much nitrogen is actually there.”

An element essential to plant growth, nitrogen ranks behind only carbon, hydrogen and oxygen in the total quantity needed, and is the mineral most demanded by plants. Nitrogen deficiency symptoms include uniformly pale green or yellow leaves, slow crop growth and reduced yields at harvest. On the other hand, lower yields and lesser crop quality can result from too much nitrogen.
If there’s more nitrogen in the soil than the crop needs, the excess may wind up in ground or surface water. Nitrogen behavior is complex, but must be understood so producers can manage nitrogen for maximum profitability and minimal environmental impact, the Mississippi State University Extension Service noted in a 2012 bulletin.

Nitrogen develops from decomposing organic materials such as manure, plants, human waste and ammonia or ammonium. Plants need nitrogen for growth-essential amino acids and proteins, but cannot use organic nitrogen directly. Microorganisms in the soil convert the nitrogen to ammonium.

Certain microorganisms convert ammonium to nitrate, which contains nitrogen and water. Since nitrate is water-soluble, excess nitrate not used by plants can leach through the soil and into the groundwater, according to a University of Wisconsin Extension Service newsletter.

The U of I study was to determine how much nitrogen is in the soil now, to estimate loss over the winter and early spring, and to estimate the amount of nitrogen available to the 2013 crop, especially if corn is planted in the same fields. Some loss typically occurs with normal precipitation from fall to early spring, but if this winter is dry, some of the nitrogen there now should be available for the 2013 crop.

Statewide testing
Soils in approximately 200 sites across Illinois were tested in the project. November 2012 was relatively dry in Illinois, with few reports of tile lines draining water from the fields. Now that soils have cooled down, the nitrogen – mostly in the form of nitrate – probably will stay in the soil unless enough moisture occurs to drain through the tile lines, taking along some of the nitrogen.

“We know we have to find out how much nitrogen there is in the spring. How much is there in the fall is of interest, but if it all disappears by spring, then we can’t take any credits for it. Part of the thinking after a drought like this is, if things have really changed in the soil,” Nafziger explained.

“(Nitrogen change) is just one of the things we know tends to happen. Whether it’s of great importance to farmers depends to a large extent if they plan to have corn or soybeans in that field the next year. Beans will take up the nitrogen that’s left over by the corncob, but they probably won’t produce higher yields because of that.

“The greatest interest is where they plan to follow corn in those fields next year, and we’ll be looking very closely in the spring to see how much nitrogen is still there. We’ll need to put fertilizer on, which is what we need to do anyway for corn, but our hope is if we find some, of course we can use less nitrogen in the fields next spring,” he concluded.

Soil samples showed about 20-30 pounds of soil nitrogen per acre in some of the fields tested, and more than 200 pounds per acre in other fields. There is no way to be sure about the amount of nitrogen in a specific site without sampling the soil.
“By next spring, we’re going to know that if (the climate) continues to be dry, and we can sample the fields that we sampled in the fall and find there’s still quite a bit there, I think we’re going to put out rather general information that if you’re in these areas where we found high amounts of nitrogen, you might want to take a sample before you apply (commercial) nitrogen and see just how much might just be left (in the soil),” he said.

The information will be published in a U of I bulletin, which Nafziger said the public can access anytime.

To find nitrogen levels, producers can take their own soil samples or contact their local fertilizer company, which might do this. To actually take samples is the only way to know the level of nitrogen in a given location.

“We encourage people in this project to just go to a place in the field to where they know they put on a certain amount of nitrogen – not on the end rows or anything, but choose a spot and take a couple samples in that spot,” he said.

“Take something like a pound in a sample. Using a soil probe, we’re taking samples from the top foot. Those who are able are taking a sample from the second foot – a sample below the top sample in the same hole. This way they can take out one sample from one foot and another sample from two feet.”

The university does not release names of producers involved in the nitrogen testing program.

“The nitrate we find out there today, if we get a lot of rain ever again, is pretty susceptible to being moved down into tile lines and out into the drainage river systems,” Nafziger said. “People don’t want to be fingered as a source of the problem.

“Farmers are very responsible on how they use nitrogen. But in a year like (2012), it didn’t matter how responsible we were – there’s still quite a bit left in the fields.”