The accuracy of mechanical analysis depends on the complete dispersion and stability of the soil suspension in order to make the separation of the soil fractions possible. The purpose of this study was to evaluate the efficacy of adding sand in different amounts and particle sizes in the dispersion phase of the soil textural analysis in attempt to improve the accuracy of results. The soils used were Rhodic Eutrudox (oxidic) (LVef), Anionic Rhodic Acrudox (LVwf), Rhodic Eutrudox (kaolinitic) (LVe), Arenic Hapludalf (PVAe) and Rhodic Kandiudox (NVef). Sodium hydroxide and rotation shaking (60 rpm) for 16 hours with addition of sand were used in the dispersion phase. The experiment was set up in a complete randomized design, arranged in a factorial 6 x 2, with three replications. The amounts of sand particles used in the dispersion phase were: 5, 10, 15, 20 and 25 g and the sand particle diameters were 2.0 to 1.0 mm and 1.0 to 0.5 mm. According to the adjusted model, the addition of sand particles (diameter 1.0-0.5 mm) at amounts of 21.4 g to LVef, 19.6 g to LVwf and 25.8 g to NVef increased the soil clay content by 50, 38, and 14.5 %, respectively. No sand was added to LVe and PVAe, since clay dispersion was not a problem in these soils. Results indicated that the addition of 25 g of sand (particle diameter 0.5-1.0 mm), during the dispersion phase of the soil granulometric analysis of clayey soils with high iron oxide content and limited dispersion, is efficient to disperse the soil fractions.
texture analysis; clay; mechanical dispersion; iron oxide soil; microaggregation
