The complete sample dispersion and maintenance of stability in the dispersed phase are fundamental for a greater accuracy in soil texture analysis. For this purpose, Na+ and Li+ compounds were tested as alternative chemical dispersants, compared to a 10 mmol L-1 NaOH solution, for the possibility of a more effective dispersion and to minimize the presence of pseudo components, basically pseudo-silt, in the particle size analysis of Oxisols. Eight samples of Oxisols from the State of Minas Gerais, selected for their different parent materials and iron oxide contents were used. The treatments were arranged in a randomized block design, corresponding to a 2 x 8 x 7 factorial arrangement, with three replications. The factors consisted of eight Oxisol samples, collected in the horizons A and B, and of seven dispersants. NaOH was used as reference dispersant and the alternative dispersants tested were LiOH, NaClO, [NaClO + NaOH], [HCl + NaOH], (NaPO3)n and [(NaPO3)n + NaOH]. None of these identified the effectiveness of dispersants as well as NaOH when using the highest clay proportion. The sequence of effectiveness was ranked as follows: NaOH > [(NaPO3)n + NaOH] > [HCl + NaOH] > [NaClO + NaOH] > LiOH > (NaPO3)n > NaClO. Among the alternative dispersants, the solution [(NaPO3)n + NaOH] performed similarly to the reference dispersant, highlighting the importance of raising the pH values to near 12. The effectiveness of the other sodic solutions with high pH, [NaClO + NaOH] and [HCl + NaOH], was reduced when raising the osmotic pressure of the solution, hampering soil dispersion. The performance of LiOH was worse than of the reference. This response can be explained by the tendency of this alkali cation to form covalent bonds that block negative electric charges from the clay exchange complex, decreasing surface charge density. The dispersants (NaPO3)n and NaClO were the least effective, due to the lower solution pH. It was concluded that NaOH is most effective in dispersing soil with clays with pH-related cation exchange capacity, since it tends to increase negative charges, repulsion between particles and consequently soil sample dispersion, at a relatively low osmotic pressure of the suspension.
Soil texture analysis; sodium hydroxide; lithium hydroxide; sodium hexametaphosphate; sodium hypochlorite; hydrochloric acid
