Soils can become clayey because, over time, excess sodium causes clay in the soil to become dispersed. When clay disperses, the individual clay particles are no longer held together, thus releasing them to move through the soil and concentrate in a single dense layer. Frequently, this layer of dispersed clay is so dense that the movement of water and oxygen is severely limited.
All soils, especially clayey ones, can benefit from tillage before planting. Sometimes, too, soil tests may show that a soil has too much nitrogen or other substances for optimum growing. Studies have shown that what can really help improve soil over the years are high levels of organic matter. But as of yet, no case for gypsum as a regular amendment for clay-like soils has been found.
Ray Ridlen is an agriculture/horticulture educator for the Oklahoma County Extension Service. His column addresses frequently asked horticulture questions. For more information, call 713-1125.