Uso de energia ultra-sônica e turbidimetria na análise textural de pequenas amostras de solo.

There are special situations in the laboratories of soil analysis, in which methodologies traditionally used do not attend the established purposes, mainly if one desires to perform particle-size-distribution in the material that was previously submitted to other analysis, which is common in researches. Too small samples can generate difficulties upon dispersion efficiency through conventional mechanic shakers and result in exceeding reduced quantities of clay to be quantified, being desirable to adapt technics which allow such investigation. Taking that into account, this study aimed to determine the soil particle-size-distribution in such small samples. For that purpose, samples of A and B horizons from different soils were submitted to two procedures for soil particle-size-distribution: the first one using the fast shaking for dispersion and the pipette method (referential) to quantify the clay fraction, and the second one, where the samples were dispersed by sonication, being the clay fraction determined by turbidimetry. The alternative methodology was efficient for clay determination. The obtained differences in clay amount between the methods were significantly correlated with the aluminum forms determined in soils. [ABSTRACT FROM AUTHOR]