Application of gypsum and lime to increase cation adsorption of a Geric Ferralsol in the Brazilian Amazon region

Abstract

A Brazil-nut plantation 140 km east of Manaus was the site of a 3-month field trial, in which a by-product gypsum and a lime were compared. The soil properties in the plantation, 23 years after slash-and-burn, are not basically different from the remaining primary forest. The comparison is impeded by a distinct spatial variability of the soil nutrient content within the plantation. A linkage between Effective Cation Exchange Capacity (ECEC) and sulfate content of the soil is presumed. Gypsum-application increases the exchangeable Ca considerably, which is not an effect of Al-exchange, but of newly created adsorption sites. The potential of gypsum to increase the ECEC corresponds on a 1:1 basis with the potential for sulfate adsorption in the soil. Mg and nitrate are strongly leached after gypsum application. The applied, extremely fine ground lime has almost no effects below 5-10 cm depth. Ca, Mg and, to a lesser extent, K exhibit a much enhanced adsorption when applied as sulfate instead of chloride. All three cations are preferentially adsorbed in the subsoil, where the ECEC is only half the value of the upper soil. For fertilization concepts of those soils, the subsoil deserves much greater attention. The infiltration pattern of an organic dye gives evidence of a strong influence of bypass water flow through macropores in the soil. © WILEY-VCH Verlag GmbH, 1999.