Rational soil management in the humid tropics.
1994
Van Ranst E.
The highly weathered soils of the humid tropics have a colloidal composition whose surface charge properties are quite different from those of the majority of temperate soils. The most important chemical properties of these tropical soils associated with their mineralogical composition are : (1) a low reserve of nutrients, (2) a high phosphorus adsorption, (3) a low cation exchange capacity, and (4) a high point of zero charge. The catastrophic decline in organic matter as a consequence of prolonged cropping of these soils or through erosion, not only reduces the ability to supply nitrogen, phosphorus and sulphur for crops, but also the ability to retain cations in an available form. The frequent application of small amounts of fertilizers brings about a temporary improvement, but does not alter the fundamental problem, being the bad fertilization status resulting from the nature of the colloid surfaces. A more rational management can be obtained by trying to change the nature of the colloidal surfaces, leading to an increase of the cation exchange capacity. This might be achieved by blocking positively charged sites (application of P fertilizers), or in a more alternative way by adding ground, young volcanic pyroclastic materials, a better management of the organic matter and a more efficient erosion control.
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