Management of gypsiferous soils
- Pale brown Gypsisol in loess with porous massive structure, China
Soils with more than 25 percent of gypsum may hamper plant growth. The soil material then lacks plasticity, does not stick together and becomes completely unstable in water. Consequently erosion of gysiferous soils can be very severe. Soils with significant amounts of gypsum particularly occur in the driest areas on earth.
Improvement in the productivity of gypsiferous soils in rainfed conditions may be achieved by:
- Soil terracing on the deep hilly soils to prevent erosion.
- Supplementary irrigation where water resources are available.
- Harrowing the land after harvesting and before the rainy season to improve the infiltration of water and conserve soil moisture.
- Replacement of fallow by small-grain leguminous crops in wheat-fallow rotations to improve soil organic matter.
- Subsoiling to break the cemented gypsic subsoil to improve root penetration and reduce susceptibility to drought.
- Use of fertilizers, especially nitrogen and phosphorus for cereals.
Where irrigation water is available, leaching of gypsum is necessary to keep the salt content low. An effective drainage system is required to maintain a relatively low water-table and keep salinity under control. Cavities created by leaching gypsum from the surface soil make it necessary to level the land surface each year. Irrigation canals must be lined to prevent the canal walls from caving in. Soils with a cemented gypsic layer may impede the installation of drainage systems. Under irrigated agriculture on gypsiferous soils with a low level of organic matter and total nitrogen, the regular application of N fertilizers is essential to secure adequate yields of most crops. The potential productivity of gypsiferous soils is related to the depth of the gypsic layer. In soils with a gypsic layer below 60 cm depth, the plant roots penetrate freely and there are sufficient soil volume for nutrients. Fertilization of these soils improves plant growth and increases yield. In shallow soils, with a gypsic layer near the surface, the soil volume is limited and plants do not thrive generally.
When Gypsiferous soils contain only little gypsum in the upper 30 cm soil layer, they can be used for production of small grains, cotton, alfalfa, etc. Dry farming on deep gypsiferous soil requires use of fallow years and water harvesting techniques, but is rarely rewarding under adverse climate conditions. Many gypsiferous soils in (young) alluvial and colluvial deposits have relatively little gypsum. Such soils can be very productive if carefully irrigated. Even soils containing 25 percent powdery gypsum or more may still produce excellent yields of alfalfa hay, wheat, apricots, dates, maize and grapes, if irrigated at high rates in combination with forced drainage. Application of fertilizers is required for good yields. Most areas of gypsiferous soils are in use for extensive grazing.