In addition, Kentucky’s fragipan subsoils are often acidic, which can further restrict plant root growth and water uptake.

In a study funded by the Kentucky Soybean Promotion Board, Grove and fellow UK Soil Scientist Edwin Ritchey conducted small-plot research in 2012 to determine if the addition of either gypsum or poultry litter or both could lower the fragipan depth and increase corn and soybean production.

Previous studies in other countries have shown gypsum can reduce the effects of acidic soil on corn crops. In an unrelated study at the UK Research and Education Center in Princeton, researchers made a chance observation that poultry litter might increase the depth of the fragipan in the soil profile.

Grove and Ritchey’s 2012 study occurred on 128 plots (64 plots for each crop) at the UK Research and Education Center at Princeton on a Sadler silt loam with a fragipan. They amended crop-specific plots with 16 replications each of 3 tons of gypsum, 3 tons of poultry litter, both or neither. They will repeat the study during the 2013 growing season.

In the 2012 study, soybean plots that received poultry litter only and plots with poultry litter and gypsum yielded two more bushels per acre than plots without either amendment or only gypsum.

Grove noted that because the 2012 drought was so severe, there was not a significant amount of moisture to move the gypsum and/or soluble poultry litter constituents deeper into the soil. When the amendments move deeper in the soil, greater yield returns are expected.

“We know from studies in Brazil and Africa that if you’re going to see any benefit from gypsum, it should appear by the second year,” Grove said. “We’re hoping rain this winter will help move the soluble constituents deeper into the soil so that we can see benefits from gypsum this year.”

If the amendments cause the fragipan to move deeper into the soil, researchers hope to learn if the movement is caused by the fragipan actually dissolving or dissolving and reforming at a deeper depth.

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