November 21, 2001 | By: Laura Skillman

Every two years, a committee of agronomists and horticulturists from the University of Kentucky College of Agriculture meet to review the university's fertilizer recommendations to see if any changes should be made based on ongoing research.

These recommendations are contained in the College of Agriculture's publication AGR-1 which is available at county offices of the Cooperative Extension Service and the UK College of Agriculture web site at

Earlier this month, the committee members met to consider whether to change the university's nitrogen recommendations for corn. Industry representatives are also invited to these biennial meetings.

The members also review other issues that may require changes. An example would the governmental programs, such as when buffer strips were added to the mix a few years back.

The concern with UK's recommendations for nitrogen on corn was that yields have increased dramatically in the past 15 to 20 years yet the recommendations have not, said Lloyd Murdock, a UK Extension agronomist and co-chair of the committee.

"The question was are these recommendations adequate," Murdock said. "We had the same concern and saw the need to review them."

Another issue with the nitrogen recommendations is their relationship to environmental rules such as the agricultural water quality plan along with confined animal feeding operations (CAFOS) and animal feeding operations (AFOS) regulations. In some of these regulations, farmers could be required to use UK's recommendations, he said.

"We were aware that was happening, so in the last two years there's been a considerable amount of research to see if we are behind the times, so to speak," Murdock said. "Usually, what we find is that we are not and that is pretty much what happened this year."

The main concern was not UK's nitrogen recommendations for poorly drained soils but on its recommendation on well drained soils, he said. Poorly drained soils have been found to sustain significant nitrogen loss after application each. UK recommends a maximum of 200 pounds per acre on poorly drained soils.

On well drained soils the university recommendations have been 125 to 150 pounds per acre on no-tillage and 100 to 125 on conventional tillage. Most of the work in the past two years was in no-till and that research has found that the recommendations are close but maybe a little low, Murdock said.

The recommendation was adjusted to 125 to 165 pounds per acre on fields where conservation tillage was used on well-drained soils. Recommendations in other drainage classes remain relatively unchanged.

The production categories also were changed to conservation tillage with more than 30 percent residue cover and intensive tillage with less than 30 percent residue. This replaced no-till and conventional tillage categories which did not reflect many of the conservation tillage practices taking place in Kentucky, he said.

"In looking at our research the last two years, even though the nitrogen rates are perceived to be low with increased corn yields, what we have found is that they are pretty solid," Murdock said. "Certainly a lot of people wonder how you can get 200 and 250 bushel corn yields off 160 pounds of nitrogen but we did that and consistently. When we looked at economic returns from different nitrogen applications and yields, what we found was that 160 pounds per acre gave us the most economic return by quite a few dollars.

"When you went to 200 pounds per acre, yield increased but the added cost of nitrogen brought it down to where profits weren't any greater than when 120 pounds was used, a rate most people wouldn't think about using," he said.

"We recommend less than many people do and less than many people use, but they are the most economical rates that we can find," Murdock said. "It's strictly a scientific method on which we make recommendations."

The changes will be reflected in the 2002-03 issue of AGR-1.


Lloyd Murdock, (270) 365-7541