Use of flue gas desulfurization (FGD) by-product gypsum on alfalfa

Subsoil acidity in northeast United States has been associated with decreased yield and decreased water and fertilizer nitrogen (N) utilization by forages. Surface applications of gypsiferious products has been shown to reduce subsoil acidity largely caused by high levels of soluble aluminum (Al). Our objective was to test the effectiveness and safety of using FGD gypsum to increase dry matter (DM) yields of alfalfa (Medicago sativa L.). Four and one-half, 9, and 18 mt/ha of either commercially available agricultural gypsum or two gypsum by-products were applied to a Rayne soil (Fine-loamy, mixed, mesic Typic Hapludult) with a strongly acid subsoil. Agricultural and FGD gypsum increased alfalfa DM yields by as much as 21 and 14%, respectively. Correspondingly, in the subsoil, soluble Al decreased and calcium (Ca) content and Ca:Al ratio increased. Heavy metal concentrations in either the alfalfa or soils were not increased by any treatment. However, S in the alfalfa grown at the highest treatments approached concentrations that are considered to be toxic to grazing animals.