Occurrence of Soil Tumors Northeast of the Guánica Lagoon, Lajas Valley, P.R.

Abstract

The appearance of tumors or soil mounds oozing soil-water suspensions was observed during the course of a recent soil survey of Lajas Valley. The area affected lies northeast of the Guánica Lagoon and is generally covered by halophytic vegetation. Piezometer batteries installed in the area indicated a rather high upward pressure gradient throughout. This pressure is so high during rainfall, or when the sugarcane growing at the adjoining upper lands is irrigated, that water bursts through the soil, carrying along large quantities of soil particles in suspension. Studies of the mechanical composition of the soils from the tumors and from adjacent sites indicate that the majority of the moving particles are in the clay-size range, although some silt and even very fine sand are forced upward from lower depths. Most of the movement is limited, however, to the upper 48 inches. The organic-matter and nitrogen levels are higher in the soils adjacent to the tumors than in the tumors themselves, but in both there is a sharp reduction below the 24-inch depth. The cation-exchange capacities of soils from both sites are rather high, with a predominance of exchangeable sodium in the complex, and but little calcium, magnesium, and potassium. The high exchangeable-sodium percentage, together with the lower salt content of the tumors, as indicated by conductivity of soil extracts, accounts for the highly dispersed nature of the soil. The saturation percentages are extremely high, over 100 percent in most cases. They can be explained on basis of the extremely high clay percentages of the 2:1 expanding-lattice clay mineral types present.