I’ve known that calcareous or calcite soils exist across the world. These soils are located in arid environments where insufficient rainfall fails to leach out the calcium carbonates. We have a farm in Northeast Nebraska in which the soil is calcareous. Lime flakes are very common on the soil surface and through the upper 8-inch soil profile. Calcite is not very soluble so it takes a long time to break down and can exist for decades before weathering and dissolving.
But I learned recently that there are gypsiferous soils as well. In most cases gypsum in these soils is associated with other salts of calcium, sodium and magnesium; all cationic salts that can add to salinity. Calcitic and gypsiferous soils do not occur under wet and humid climates as the rainfall would have dissolved and leached the minerals down through the soil long ago.
Gypsiferous soils arise in areas of gypsum deposits and when there is not sufficient soil depth or drainage for the calcium and sulfate to leach. Instead they accumulate in the soil profile or form layers. Garn Wallace, of Wallace Laboratories in El Segundo, Cali. Said “They (gypsiferous soils) are common in poorly drained areas and in some sub-soils. They are not common among most farming soils.”
Calcitic and gypsiferous materials accumulate because of the evaporation of mineralized surface water or groundwater containing calcium. This calcium can combine with sulfate forming calcium sulfate. Evaporation of inland seas millions of years ago is the most common cause of limestone and gypsum deposits found in nature. In these areas, gypsum particles or layers can exist through the soil profile and can have an impact on the physical (structure) and chemical (salinity) properties of the soil as a medium for plant growth.
Gypsiferous soils can contain anywhere from 1% to more than 25% gypsum and at high levels of natural gypsum may not be suitable for crop production but at low levels are suitable for crop production. Rainfall and irrigation will leach the gypsum salts down into the profile and out of the root zone but during dry periods they can move back up. Building organic matter and managing fertility will help crop production in gypsiferous soils.
Bottom line: we don’t see much agriculture, if any at all, in areas that would contain gypsiferous soils.
Dr. Davidson posts articles on soil health and management related subjects. If you have suggestions for topics or questions, feel free to contact him at [email protected] or call 402-649-5919