Use of Soil Electrical Conductivity to Determine Gypsum Movement.

There has been renewed interest in the land application of industrial by-products, such as flue-gas desulfurization (FGD) gypsum. Some of these materials can be beneficial to crop production under certain circumstances. However, recent findings show that annual applications might be needed to provide the most benefit to crops. Therefore, the objective of this study was to determine the movement of a single application of FGD gypsum, fly ash and agricultural gypsum at different rates. Our hypothesis was that higher application rates should have longer residence times in the upper soil layers (root zone) than lower rates. A commercially available tractor-pulled instrument was used to measure field EC on plots within a Bermudagrass (Cynodon dactylon L.) hay stand that had received different rates of these materials. Soil samples were collected to a 90-cm depth and partitioned in several increments to measure soil EC under laboratory conditions, as well as soil calcium concentration. Preliminary results indicate that EC can be used to determine movement of these soil amendments and that a single application of gypsum, even at a high rate, might not be sufficient to have long-term effects.