January 17, 2001 | By: Laura Skillman

Over the years, many Kentucky farmers have developed some system of rotating crops within fields with a common rotation being corn, wheat and soybeans.

But some farmers are opting to go into the same field time after time with the same crop, and changes in federal farm legislation that decoupled specific cropping requirements with farm payments could be the reason for the change, said Richard Trimble, University of Kentucky Agricultural Economist. Trimble said farmers need to consider the benefits of crop rotation versus monoculture as they look at their enterprise budgets to determine what is best for their operations.

Crop rotation and its benefits were a large part of the discussions at the annual wheat conference recently at the UK Research and Education Center in Princeton.

Generally, yields are boosted by changing crops rather than growing the same crop year after year, said James Herbek, UK agronomist. Those benefits have been known for years.

"We do have a rotation effect," Herbek said. "I don't think we know for sure why, and it's not the same for every situation when rotating crops, but we do get increased yields. You need to consider this in your enterprise budget."

Nutrient management changes also are needed if farmers change from their rotational patterns.

Nitrogen needs along with agricultural lime change when farmers go to corn after corn, said Lloyd Murdock, UK soils specialist. Extra nitrogen, from 20 to 25 pounds, is needed in corn after corn and nitrogen costs are soaring. Extra agricultural lime also is needed when farmers chose to grow continuous corn.

In addition, continually growing a single crop can increase weed, disease and insect problems.

What makes a rotation work from the insect standpoint is that, by and large, it changes the type of plant, for example, from a grass (corn and wheat) to a legume (soybeans). Rotations help reduce or control insects that feed only on limited plant types, said Doug Johnson, UK Extension entomologist. It also helps if the insects in the feeding stage are not very mobile and if the eggs are laid before a new crop is planted.

Corn rootworm is the most difficult insect to control and the most dangerous that farmers have to contend with in Kentucky if they have continuous corn, he said.

The increased pressure of insects can lead to increased use of pesticides and that adds to cost, environmental and food safety concerns, Johnson said. It also means increased handling of pesticides and the added worker protection liability, as well as increased equipment needs and density of corn planting, he said.

In soybeans, there are no current pests like corn rootworm, he said. But, there is the question of whether it could lead to the emergence of new pests.

Rotations have helped to control weeds and helped reduce the number of herbicide resistant weeds. In Kentucky, with the traditional corn, wheat and soybean rotations, only three resistant weed biotypes have been confirmed, said James Martin, UK weed specialist. While in Indiana, eight have been confirmed; nine in Illinois and five in Tennessee, he said.

Crop rotation is most beneficial in controlling disease organisms that survive in crop residue, said Don Hershman, UK plant pathologist.

In soybeans, cyst nematode is the biggest disease concern in Kentucky. Monoculture in fields that contain nematodes can result in huge increases in nematode numbers in a single year, Hershman said.

"If you ignore the possibility that diseases are going to be an extra factor if you don't rotate, I think you are mistaken," he said. "All the evidence indicates diseases of soybean and corn will be generally higher when crops are grown in monoculture. As disease levels increase, your yields will decrease. So, crop rotation is a key."

Anyone wanting more information on the benefits of crop rotation can contact their Cooperative Extension Service office.


Richard Trimble, Lloyd Murdock, James Herbek, James Martin, Doug Johnson and Don Hershman, (270) 365-7541