July 18, 2001 | By: Laura Skillman

Variable rate nitrogen applications allow farmers to put the fertilizer where they will get the most for their money while lowering rates where additional amounts are unwarranted.

A flat rate of nitrogen may not be the best economic decision, but one most farmers use today, said Lloyd Murdock, an agronomist with the University of Kentucky Cooperative Extension Service.

Research being conducted by specialists at the University of Kentucky Research and Education Center in Princeton is varying nitrogen levels based on previous yield maps found on the Trigg County farm being used in the project.

The project builds on a study by Murdock and Paula Howe, Extension soils associate. That project looked at the relationship between soils and yield variability in fields. After looking at some 20 different soil types, Murdock said they found that it all depended on topsoil depth and drainage.

"The deeper the topsoil, the better the yields," he said. "So, it logically follows that a farmer would need to put high nitrogen rates where there are high yields and low nitrogen where there are low yields. So we started this project to look at rates strictly based on past yield history."

Farmers could save money by cutting back on those areas that do not benefit from added nitrogen, Murdock said and the project's aim is to identify areas where applying extra nitrogen will produce larger yields and identify areas where extra nitrogen will not help.

Trigg County farmer Wayne McAtee said he agreed to assist with the project because he was interested in what they where doing.

"I think is has potential both for an economic impact and a possible environmental aspect with the emphasis on nitrates at the present time," he said.

McAtee said he was also a technology junkie and was anxious to get his hands on the equipment that is being used in the project.

Initially, researchers theorized that the highest producing soils would show the greatest response to added nitrogen but the reverse proved true.

By increasing nitrogen levels from 100 to 170 pounds per acre, the lowest yielding areas of the three soil types showed a 10 bushel per acre increase. That increase would more than pay for the increased cost of the extra nitrogen, Murdock said.

The highest producing areas showed only a four bushel increase from the high nitrogen rate. While the medium producing soils showed no response from the extra nitrogen, he said. A wider range of nitrogen rates are being used in the study this year.

McAtee said the first year's results surprised him but he also reminds himself that it is only one year's figures.

"I think it's going to be a lot more complicated than I thought," he said. "I'm not an agronomist and I'm finding out how little I do know. It's not as straight forward as I thought."

Murdock said the first year results prompted him and Howe to wonder if the release of nitrogen from organic matter was playing a role.

Murdock said similar results have been seen in two years of research conducted by Southern Illinois University.

That means there is organic nitrogen in high yielding areas that is being released. Many tests are available to test soil for nitrogen but none have been real successful in telling you what you need to do in a coming year to be able to adjust nitrogen rate.

However, a new test has been developed by a researcher at the University of Illinois which looks at amino sugars, an organic type of nitrogen that is readily decomposable making it a good measure of what would be released from the organic matter that year, Murdock said.

The testing is not far along in research but looks promising, he said, so the test has been added to the UK project.

"Our hope is we can identify amounts of nitrogen being released in areas of the field and adjust rates accordingly," Murdock said. "We've always assumed that fields are the same but they aren't. Now the question is can we identify those areas that release a lot of organic nitrogen and lower rates there, and identify places that aren't going to have a lot of nitrogen and increase the rates there.

"That's our hope and our theory," he said. "If it works, it would be very helpful to farmers to identify these areas.

The three-year project is one of numerous project funded through a precision agriculture grant. In 1999, U.S. Sen. Mitch McConnell announced a $1 million grant from the United States Department of Agriculture for precision agriculture research at the University of Kentucky's College of Agriculture.


Lloyd Murdock, 270-365-7541