Gypsum was used by researchers Olsen and Watanabe in the 1970s Colorado to reduce iron chlorosis in sorghum. Gypsum consistently increased iron uptake into the plant. Increases were from 4% to as high as over 700% in some soils. Increases in plant growth were from 12% in some soils to over 600% in other soils. Manganese and zinc uptake were also increased significantly. Zinc uptake was increased by an average of 41% and manganese uptake was increased 28% on average. pH of these soils averaged 7.6 and ranged from 7.3 to 7.9. Rates of gypsum used were to achieve a 30 ppm sulfur level in the soil. This would be equivalent to 1-2 tons of gypsum per acre.

Dr. Dick Weise followed this study with a research project in the Platte River Valley in Nebraska in 1982 and 1983. He used pelletized gypsum in a band beside the row in 1982 and in the row at planting in 1983. The yield results of his study are below:

More recent research has revealed that bicarbonate has a direct role in inducing iron deficiency. Bicarbonates are produced in high pH soils especially under more moist conditions. Gypsum (CaSO4 2H2O) has shown to react with bicarbonate (HCO3) to form CaCO3 or lime decreasing the amount of bicarbonate that affects iron uptake and iron availability.

These pictures show fields of soybeans where PRO CAL 40 was applied at rates from 1 to 3 tons/A. In the field near Herman, NE the PRO CAL 40 was applied prior to the previous crop of corn showing that the effect can be experienced for many years.

Other research has shown that broadcast rates of gypsum will improve infiltration and internal drainage. This will allow soils to warm more quickly which will also improve nutrient availability and plant growth.