Gypsum Effects on Crop Yield and Chemistry of Soil, Crop Tissue, and Vadose Zone Water: A Meta-Analysis.

Gypsum has various potential benefits as a soil amendment, but data are lacking on gypsum effects on crop yields and on environmental impacts across diverse field sites. Gypsum studies were conducted in six states using a common design with three rates each of mined and flue gas desulfurization (FGD) gypsums plus an untreated control (check). High gypsum rates varied among studies from 1.12 to 22.4 Mg/ha.  Gypsum was applied once at the beginning of each study and then data on component chemistries and crop yields were collected for two to three years. Meta-analyses used the response ratio (treatment value/control value) for each element or yield as the response variable and tested their significance with z values.  Various elements (including As, Be, Cd, Co, Fe, Pb, Se, Tl for crop tissue and water) were not included in the meta-analyses because concentrations were usually below the detection limits. Most response ratios varied only slightly from 1.0. Gypsum had greater effects on vadose zone water than on soil or crop tissue for several elements (11 for water, 7 for soil, 8 for crop tissue). The highest response ratio for vadose zone water was 4.22 (S), for soil was 1.57 (Ca), and for crop tissue was 1.35 (Sr). Increases in soil, crop tissue, and water occurred for Ca and S by both gypsums and for Sr by mined gypsum. The lowest response ratios in crop tissue were for Mg (0.89) with FGD gypsum and for Ni (0.92 or 0.93) with both gypsums. Sb was increased in plant tissue by mined gypsum. Both gypsums increased Ba, Cr, Mg, Ni, Sb, and Sr in vadose zone water. Mercury (Hg) was not significantly (P < 0.05) affected by gypsum additions. Yield response ratios of 0.987 for mined gypsum and 1.00 for FGD gypsum were not significant.