FGD Gypsum Application to a Tunica Clay Soil in the Mississippi Delta.

The Lower Mississippi River Basin is an intensively cropped region in the central United States. Hypoxia in Mississippi Delta water bodies is heavily influenced by nitrogen and phosphorus input from agricultural runoff. Soils within the Lower Mississippi River Basin that are adjacent to the Mississippi River or its tributaries reflect their alluvial origin. Some of these soils are characterized with high shrink-swell clay content. A corn (Zea mays L.) field study was established in 2014 near Stoneville, Mississippi, on a Tunica clay soil with the goal of evaluating the impact of FGD gypsum on the solubility of P and its potential loss in runoff. The study arranged with a randomized complete block design with three replications. Treatments included (a) vegetative buffer at the end of the corn row or bare soil, (b) 6 tons acre^-1 (13.44 Mg ha^-1) FGD gypsum applied annually in corn field area or no gypsum applied, and (c) gypsum applied in the buffer soil at the end of the crop row or not applied if there was no buffer. Gypsum was applied in the fall after harvest and tilled into the soil. Soil was sampled in the fall before and after gypsum application and characterized. Three years of gypsum application did not significantly influence most soil nutrients or physical characteristics in the Tunica clay soil. The only exception was Mehlich-3 extractable Mg, which was lower in the gypsum treated soils. These results indicate that applying gypsum to high shrink-swell clay soils may not be a recommended management option.