N. AhmadDepartment of Soil Science Faculty of Agriculture, University of the West Indes, St Augustine, Trindad, West Indes
Vertisols and other clay soils with vertic properties are among the most important soils in the Caribbean region. They are developed on many parent materials, including Recent marine clays, lacustrine sediments, marls, corals, calcareous shales and volcanic ash. Many of the soils occur in humid climates which are presently too wet for synthesis of montmorillonite, but this clay material has been inherited from the parent materials. The soils range from highly acidic for those developed on lacustrine and leached marine sediments to alkaline for those on calcareous materials. Phosphorus and K contents vary: P contents are high in the soils derived from calcareous materials and low in those formed on other materials, while the situation is the reverse for K. The clay mineralogy shows varying amounts of montmorillonite and kaolinite for those soils on calcareous and volcanic materials, while those on sediments also have illite.
With appropriate management, a wide range of crops is grown on these soils. Since large areas. are flat, rice cultivation is important. Sugarcane is an important crop also, but elaborate land layout is needed to aid external drainage. The crop is usually cultivated on highly cambered beds with ridges, and the required field drainage can occupy up to 20% of the land space. All other cropping is done on some form of cambered beds and/or ridges or banks designed to improve external drainage.
Soil fertility management requirements vary according to the particular soil type. Nitrogen losses are great from the calcareous-derived Vertisols and losses due to surface wash may be important. Phosphorus response is indicated by chemical analysis for some of the soils, but field response is not always obtained. Potassium content varies widely, but crop response to fertilizers is only obtained on some Vertisols developed on coral. Those on clay sediments are well supplied.
