Organic Matter, Agricultural Use, and Dispersion of Ferralsols for Grain Size Analysis.

Ferralsols are a class of highly weathered, oxidic and often acidic and low fertility soils ubiquitous of the tropical environments. Ferralsols can present anomalous behavior when dispersion is performed for grain size analysis using settling methods. This study evaluates the effect of total dispersion and dispersed solution stability of two Ferralsols from Brazil, under cultivated areas and native savannah vegetation with or without organic matter removal using hydrogen peroxide (H₂O₂), on percent clay, silt, and sand estimation. Samples of a Rhodic Ferralsol and an Orthic Ferralsol were dispersed using a reciprocating shaker for 16 h at 120 rpm in sodium hydroxide (NaOH) solutions. Results show that chemical modifications associated with agriculture alter the dispersion behavior of the two Ferralsols. Removal of organic matter in cultivated areas caused coagulation of fine particles. For native vegetation sites, removal of organic matter increased soil dispersion increasing clay content and decreasing sand content. NaOH was not an effective dispersant agent in all conditions and thus there is a need for investigating better chemical compounds or combinations of thereof for the dispersion of Ferralsols. Standardization of grain size analysis of Ferralsols is needed for comparisons between different studies and laboratories to be possible. [ABSTRACT FROM AUTHOR]