A recent inquiry concerned the use of gypsum in field crops. The material has been used to improve crop production in some parts of the United States. Here are a few facts about gypsum.

Gypsum is calcium sulfate (CaSO₄) and thus is a source of calcium and sulfur. When added to the soil it dissolves to form calcium and sulfate-sulfur (the sulfur form that plants can readily use if the nutrient is needed). Gypsum is not the only fertilizer source of sulfur. Soil organic matter, rainfall, and certain other fertilizers are also sources of sulfur.

In northern Illinois it is very unusual to have a calcium deficiency. If soil pH is maintained at levels for optimum crop production, calcium deficiency will be extremely rare.

When gypsum is added to the soil it becomes a neutral salt. There is no carbonate or bicarbonate associated with the calcium and it does not release hydrogen when added to the soil. Thus, gypsum has no effect on soil pH and is not a liming material. Nor does it acidify the soil.

Elemental sulfur (S) applied to the soil will reduce soil pH, but the practice is too expensive for large-scale agronomic field crop situations.

Gypsum is beneficial in reclaiming sodic or high sodium soils. When added to the soil, calcium from the gypsum replaces the sodium on the soil clay particles and with sufficient water movement through the root zone, the displaced sodium is flushed from the soil profile. Sodic soils are very uncommon in Illinois. These soils are typically found in arid climates.

Field studies in the Midwest show that gypsum does not affect soil compaction-soil tilth and that a particular calcium-to-magnesium ratio is not critical to crop production.

Is there a role for gypsum in agriculture? Yes, but it is limited.