Crop Response to Soil Applications of Phosphogypsum
1986
Mays, D. A. | Mortvedt, J. J. (John J.)
Phosphogypsum (PG), a by-product of the phosphate industry, was incorporated with soil to determine effects of land disposal on crop growth and uptake of cadmium (Cd) and radium (Ra). Application rates of PG were 0, 22, and 112 Mg ha⁻¹. Soil was cropped sequentially with corn (Zea mays L.), wheat (Triticum aestivum L.), and soybeans [Glycine max (L.) Merr.] over a 1–5-yr period. Yields of corn were decreased at the high PG rate, apparently because of a physiological calcium-magnesium (Ca-Mg) imbalance, but yields of wheat and soybeans were not affected by PG application. Concentrations of nutrient elements and Cd in the grain of each crop were not affected by PG application; the Cd concentration of Pg was 0.23 mg kg⁻¹. Radiological assay of grain samples showed no increase in ²²⁶Ra radioactivity in any of the three crops due to PG application; PG contained 925 Bq kg⁻¹ (25 nCi kg⁻¹) of radioactivity. Analyses of soil after soybean harvest showed that the level of radioactivity in the surface 15-cm layer increased from 35 Bq kg⁻¹ in the control treatment to 73 Bq kg⁻¹ at the high PG rate; the radioactivity level in the subsurface layer was not affected. These results suggest that PG may be applied to agricultural soils at relatively high disposal rates without increasing levels of Cd or radioactivity in corn, wheat, or soybean grain. Applications of By-product PG at recommended rates of 500 to 1000 kg ha⁻¹ as a source of Ca or S for crops would result in lower levels of Cd and radioactivity than those reported here.
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