Phosphogypsum, a by-product of phosphoric acid production, was examined for its potential value as a source of sulfur and calcium in sandy, low-cation-exchange soils in Florida. Positive yield responses to phosphogypsum in field and greenhouse studies were found for several crops, including corn, potatoes, cantaloupes and watermelons. Yield enhancement by phosphogypsum was most evident when other nutrients were balanced and in adequate supply. Application of 0.5 to 1.5 tons of phosphogypsum per acre had no significant effects on radioactivity (gross alpha and gross beta emissions) or heavy metals (As, Cd, Cu, Fe, Mn, V, Zn) in sweet corn, citrus, watermelon, tomato or cowpea. The study also examined factors affecting pelletization of phosphogypsum for easier application and more efficient fertilizer blending. Phosphogypsum alone did not produce a sufficiently hard pellet, but several finely ground fertilizer additives, such as sulphate of potash magnesia, urea, magnesium oxide, olivine, manganese sulfate, copper sulfate or zinc sulfate, did result in sufficiently durable pellets when mixed with phosphogypsum.
Arvel H. Hunter, Agro Services International, Inc. November 1989.