Physico-Chemical Characteristics of Exposed Saprolites and Their Suitability for Oil Palm Cultivation

The reviews on the management of upland soils for oil palm cultivation have indicated that these soils are poor in fertility and classified as marginal to unsuitable. Our study aimed at investigating the problem, found that saprolites laying below the soil layers are either exposed directly or near to the surface as the result of unavoidable terracing of slopes to enable cropping, rendering poor crop suitability. Samples from three different saprolitic profiles of varying depth and geology were collected and analyzed for their physico-chemical properties and chemical fertility characteristics. Besides variability in characteristics of different geological origin, the saprolites have poor fertility and physical properties, suggesting that they are poor substrate for crop growth. The fertility status of the saprolites, despite less weathered, were poorer than their soils. Comparatively, they have higher phosphorus retention capacity, lower net negative charge, and thus lower cation retention capacity. The Al phytotoxic effect, however, was lower in the saprolites than in their soils. The saprolites physical properties were characterized by massiveness and lacking of structural development, which enables high water retention but may not be available to plants. The isovolumetric transformation analysis of rock into saprolites showed a significant depletion of base cations from the Profiles, instituting poor fertility status of saprolites in comparison to their respective soil layers.The suitability assessment of saprolite materials of varying geological origin indicates that saprolites are unsuitable for oil palm cultivation, with shallowness, fertility and poor drainage conditions being the major constraints.

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