Meta‐Analysis of Gypsum Effects on Crop Yields and Chemistry of Soils, Plant Tissues, and Vadose Water at Various Research Sites in the USA

Gypsum has a long history as a soil amendment. Information on how flue gas desulfurization (FGD) gypsum affects soil, water, and plant properties across a range of climates and soils is lacking. We conducted a meta‐analysis using data from 10 field sites in the United States (Alabama, Arkansas, Indiana, New Mexico, North Dakota, Ohio, and Wisconsin). Each site used three rates each of mined and FGD gypsums plus an untreated control treatment. Gypsum rates included a presumed optimal agronomic rate plus one rate lower and one rate higher than the optimal. Gypsum was applied once at the beginning of each study, and then data were collected for 2 to 3 yr. The meta‐analyses used response ratios (R) calculated by dividing the treatment value by the control value for crop yield or for each measured element in plant, soil, and vadose water. These R values were tested for their significance with z values. Most R values varied only slightly from 1.00. Gypsum significantly changed more R values from 1.00 for vadose water than for soil or crop tissue in terms of numbers of elements affected (11 for water, 7 for soil, and 8 for crop tissue). The highest R value for soil was 1.57 (Ca) which was similar for both mined and FGD gypsum, for crop tissue was 1.46 (Sr) for mined gypsum, and for vadose water was 4.22 (S) for FGD gypsum. The large increase in Ca and S is often a desired response to gypsum application. Lowest R values occurred in crop tissue for Mg (0.89) with FGD gypsum and for Ni (0.92 or 0.93) with both gypsums. Although some sites showed crop yield responses to gypsum, the overall mean R values for mined gypsum (0.987) and for FGD gypsum (1.00) were not significantly different from 1.00 in this short‐term study. Core Ideas Meta‐analysis was used to evaluate gypsum treatments at 10 sites within the United States. Response ratios were calculated for crop yields and chemistries of soil, plants, and water. Crop yields showed both positive and negative results to gypsum treatments. Most R values for elements varied only slightly from 1.0, meaning no treatment effect. Concentrations of elements in samples were below levels of environmental concern.