GENESIS, MINERALOGY, AND RELATED PROPERTIES OF WEST INDIAN SOILS

The Montserrat series is one of the most fertile of tropical soils. Substantial amounts of exchangeable K, available P, and favourable organic matter content and distribution contribute to its unique properties. P occurs in amounts ranging from 0.4 to 0.6 per cent, about 75 per cent of which is inorganic with Fe phosphates making up the bulk. Truog's reagent almost quantitatively extracts Ca phosphate and Bray's and Olsen's reagents extract mainly Al phosphate. Exchangeable K is derived from glauconite. High exchangeable Ca and Mg contents derived from weathering of carbonates impart a favourable pH to the soil for plant growth. Exceptional structural stability to 120 cm depth is associated with high free iron oxide, organic matter, and Ca contents. The outstanding feature in mineral weathering is the rapid transformation of glauconite through vermiculite to kaolinite and the formation of goethite. Considerable interlayering occurs between vermiculite with sesquioxide coatings and mica-vermiculite interlayers. Much of this weathering occurs in the calcareous, oxidized, friable parent rock. The features of the Montserrat series described above substantiate its classification as a Brown Earth (Mollisol).