Kentucky Cover Crops: Ryegrass Helps Break Up Fragipan Layers

Soil showing fragipan layer. Photo: Kentucky Corn Growers Association

Several University of Kentucky soil scientists, an economist, a forage specialist, and other experts gathered in Princeton on October 3 to share findings from research that looked at getting rid of an issue for many western Kentucky farmers, the fragipan. This research has been supported by the Kentucky Corn Growers, Kentucky Small Grain Growers, and the Kentucky Soybean Board for several years.

Drs. Lloyd Murdock and Tasios Karathanasis explained to field day farmers and participants that fragipan horizons are naturally-occurring, impermeable layers found on 1.5 million cropable Kentucky acres, and about 12 percent of U.S. land area. Not only does this cemented layer restrict water availability to plants in dry periods but also reduces water drainage when conditions are wet. In either scenario, yields are significantly reduced.

While Dr. Murdock and his team tested several chemical application methods, it was the presence of annual ryegrass that resulted in the biggest degradation of the fragipan.

They said they believe the degradation occurs through both mechanical and chemical means; annual ryegrass roots apparently contain exudates that have a degrading effect on the fragipan, and the deep root penetration also increases soil porosity and may facilitate the leaching of other effective compounds down to the fragipan.

The team is presently looking for varieties of annual ryegrass that are more effective in breaking down the fragipan and varieties that are more easily killed by burndown herbicides. How to manage the cover crop with regard to timing on planting and burndown was of particular interest to visiting farmers.

“You need your ‘A’ game to burn it,” said visiting ryegrass specialist Dan Towery, “but if you can read and follow directions, you can do it.”

Towery suggested that farmers should learn their water hardness and pH when mixing herbicide and make sure the timing is right, as annual ryegrass needs to be actively growing for efficient burndown.

Visiting Dubois County, Illinois farmer Junior Upton also talked to participants about using annual ryegrass on his farm, where corn yield increased dramatically over time.

Based on UK’s research and Upton’s data, Murdock said that it might be possible to increase yields of corn and soybeans by 25 percent on the fragipan soils by using an annual ryegrass cover crop. He also expects to improve the yields of wheat.

“A 25 percent increase would result in $500,000,000 in increased returns to Kentucky producers per year or $5,000,000,000 over a 10 year period on the 1.5 million acres of cropable fragipan soils in Kentucky.”

UK economist Jordan Shockley also discussed costs, risks, and benefits of using annual ryegrass, and he projected a $225 per acre increase over a 10-year period.

Dr. Murdock and his team will continue to share additional information as it becomes available.

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