STABLE MICROAGGREGATES AND NUTRIENT POOL IN OXISOL UNDER PASTURE IN SAVANNAH REGION

Abstract

Nutrients preserved in microaggregates are an important fraction of the pool of nutrients in highly weathered soils. With the objective of better understanding the nutrients distribution in microaggregates of fine-sand (200-50 ?m) and coarse-silt (50-20 ?m), in a Rhodic Haplustox, the present study utilized an adapted physical fractionation procedure with mineralogical and chemical characterization. Part of the soil fractions was characterized as microaggregates formed by clay and silt minerals, with high macro and micronutrients contents. P, Cu, Mn, and Zn were more efficiently accumulated in the microaggregates and less susceptive to removal by the weathering and leaching actions, when compared to K and Mg. Higher C contents were found in the superficial horizon microaggregates (50-20 ?m), showing evidences of an efficient physical protection against mineralization. Macro and micronutrients pools (total contents), in the 200-50 ?m and 50-20 ?m microaggregates, corresponded to 5-19% of the total soil nutrients content, and 24-26% of the total soil carbon was seized by those microaggregates. Although these microaggregates present a low capacity to store nutrients, they become an important and highly stable compartment to preserve nutrients, as far as physical degradation and weathering and leaching are concerned.

KEY-WORDS: Soil aggregation; physical fractionation; macronutrients; micronutrients; organic matter storage.