Determinacao do S trocável do solo pelo método colorimétrico do metiltimol azul. | Determination of soil exchangeable S by the methylthymol blue colorimetric method | Determinación de S cambiable del suelo por el método colorimétrico del metiltimol azul
1982
Bittencourt, V.C | Batista, L.F | Gurgel, M.N.A | Cordeiro, D.A.
Traditional methods Jim determinist the exchangeable S of soils lack sensitivity, reproducibility, and are too time consuming. The method described in this paper is more favorable. Blue methylthymol in a high pH (12.70) forms a complex of barium ion, and the intensity of the resulting color varies linearly, as a function of the quanta), of ion present in the solution. On the basis of this principle, S in the SO4(-2) form is determined, with a colorimeter provided with an expanded scale and a 430 mn The soil extract is obtained with HO 10(-3), in the proportion of 2.5 ml of extracting solution per gram of soil The cations in the extract constitute interferents, once they have been complexed by the methylthyma Therefore, a cation exchange resin should be used for eliminating them. The following results were obtained for the soils of the State of Sao Paulo (in ppm of S-SO4) LEa - 16 7; PVls - 13, LVa - 18 3; LR 20, Pln 22.5; PVp -24.3; TE 25 and 0 - 25. In relation to magnitude the values obtained above are consistent with those described in the literature. The variation coefficient had values of 6.40 to 0.86, with 2.36 as the mean value, which indicates that the precision of the method used is satisfactory.
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