Research Highlights

Fragipan field day held in Princeton

By Kentucky Soybean Board

Fragipan soil is found on 2.7 million acres of soil in Kentucky, and on 50 million acres throughout the United States. Uni­versity of Kentucky (UK) Extension Soils Specialist Dr. Lloyd Murdock has devoted his career to helping farmers across the state to improve their soils, and his extensive work on breaking down the fragipan makes him a leading authority on the subject.

UK held its first fragipan field day at the Princeton Research and Education Center in October, with more than 100 farmers, county extension agents and other interested parties in atten­dance.

The fragipan is a hard, cement-like layer that occurs naturally in silt loam soil. The fragipan layer is often 12 to 24 inches thick and can be found 20-24 inches beneath the soil surface. There­fore, it reduces the water holding potential in these soils to about one-half that of many of our more productive soils. It also causes saturated soil conditions in the winter and spring that can result in adverse condition to crops growing during this time. There­fore, crop yields on these soils are reduced.

If the cementation can be dissolved, it would be very similar to the soil above it. The goal of Dr. Murdock’s most recent project, funded for three years in part by the Kentucky Soy­bean Board, is to try to dissolve the cementation and make a deeper soil that will hold more water for summer growing crops and reduce waterlogging in the winter, which would make the soil better suited for winter crops.

When Murdock’s project first began, almost no research had been reported on how the fragipan can be broken down and made into soil. Progress is being made faster than expected in finding solutions to remediate the fragipan. After numerous tests in the lab, the greenhouse and the field, it has been proven that the use of annual ryegrass as a cover crop can be effective in breaking down this hard layer.

Dr. Jordan Shockley presented a session on the economic considerations of breaking down the fragipan, including estab­lishment, termination, and machinery while balancing the ben­efits of yield increase. Risks included in the equation are out­put price variability, input price variability and yield variability. Shockley said that, in some cases, it might not pay to break down the fragipan, but that in most scenarios it was a pretty safe bet. His estimate of cost to utilize annual ryegrass as a cover crop is about $36/acre, and the sample calculations that he used showed increased net profit.

Core sample research shows that repeated application of an­nual ryegrass as a cover crop could break down the fragipan lay­er by as much as 10 inches. The lab research thus far has shown an average of about six inches, and Murdock says that for every inch of depth the fragipan is remediated, farmers can expect a two to two-and-a-half percent yield increase. If we extrapolate this data, this pencils out to a big increase in yield for our state. Kentucky’s state soybean average is currently calculated at 53 bushels/acre, and we grow soybeans on nearly 2 million acres of soil. If 75 percent of those acres contain some degree of fragipan soil, and if each of those acres saw a two-percent yield increase, that would be an increase of 1 bushel per acre, for a statewide yield increase of 1.5 million bushels.

These long-term consequences and lasting results are among the reasons that the farmer-leaders of the Kentucky Soybean Board invest checkoff dollars into production research. Using those dollars to investigate ways to solve problems that affect growers here in our state is not a task taken lightly.

One farmer who is experiencing these yield increases is Ralph (Junior) Upton. Upton spoke at field day and said that he has been using annual rye grass as a cover crop for 17 years, and he has seen noticeable increases in yields in both soybeans and corn over the nearly two decade span. He makes sure to termi­nate the cover crop just as it begins to “green up” in the spring so that it won’t leach valuable nutrients meant for his cash crop from the soil, and says that Dr. Murdock has been an invaluable resource to his operation.

In summary, the fragipan is a very real problem for Kentucky producers, and it certainly appears that Dr. Murdock’s research has eliminated the trial and error method that many producers have been using to break up this layer of cementlike soil in order for cash crop root systems to better utilize water and nutrient resources.

Published: Dec 17, 2019