Actas de congresos
Revisiting Titration Procedures For The Determination Of Exchangeable Acidity And Exchangeable Aluminum In Soils
Communications In Soil Science And Plant Analysis. , v. 29, n. Nov/14, p. 1973 - 1982, 1998.
De Andrade J.C.
Van Raij B.
The use of 1 mol L-1 ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) solutions as alternative soil extractants were evaluated for the determination of the exchangeable acidity and exchangeable aluminum (Al) in twelve soil samples by the traditional titration/back-titration method. The exchangeable Al results were compared with those obtained by inductively coupled plasma emission spectrometry (ICP-AES) measurements while the exchangeable acidity results, using either NH4Cl or NH4NO3 solutions as alternative soil extractants, were compared against those using 1 mol L-1 potassium chloride (KCl) and bromothymol blue as the indicator. The results indicated that the use of ammonium (NH4) salts in these determinations is not recommended since the exchangeable acidity found using these extractants was systematically higher than that found in KCl extracts due to the additional acidity caused by the presence of comparatively higher concentrations of NH4+ ions. In addition, the reaction media also seems not to be appropriate for precise and accurate determinations of the exchangeable Al by back-titration after the addition of sodium fluoride (NaF), due to the formation of a complex chemical system composed of multiple equilibria, such as hydroxo, chloride, and fluoride complexes with Al at relatively high ionic strength. This strongly contributes to poor indicator color changes. Thus, the extraction of soils with 1 mol L-1 KCl solutions is still the best way to extract exchangeable acidity and exchangeable Al for determination by titration. The use of phenol red as indicator for the determination of exchangeable acidity in KCl extracts is recommended in place of the commonly used bromothymol blue or phenolphthalein to increase reproducibility and precision. Other procedures, such as spectrophotometric ones, have to be considered for the determination of exchangeable Al, principally if NH4 salts are used as extractants.29Nov/1419731982Bruce, R.C., Lyons, D.J., A comparison of methods for measuring AI, Ca, Mg in KCl extracts of soils (1984) Commun. Soil Sci. Plant Anal., 15, pp. 15-21Jayman, T.C.Z., Sivasubramaniam, S., The use of ascorbic acid to eliminate interference from iron in the aluminon method for determining aluminum in plant and soil extracts (1974) Analyst, 99, pp. 296-301Jones J.B., Jr., Elemental analysis of soil extracts and plant tissue ash by plasma emission spectroscopy (1977) Commun. Soil Sci. Plant Anal., 8, pp. 349-365Kamprath, E.J., Exchangeable Al as a criterion for liming leached mineral soils (1970) Soil Sci. Soc. Am. Proc., 27, pp. 277-280Logan, K.A.B., Floate, M.J.S., Ironside, A.D., Determination of exchangeable acidity and exchangeable aluminum in hill soils (1985) Commun. Soil Sci. Plant Anal., 16, pp. 301-314Machado, P.L.O.D.A., Gerzabek, M.H., Soil aluminum extraction methods in relation to plant aluminum and yield on Austrian and Brazilian soils (1993) Commun. Soil Sci. Plant Anal., 24, pp. 2661-2677McLean, E.O., Aluminum (1965) Methods of Soil Analysis, Part II. Agronomy No. 9., 9, pp. 992-994. , CA. Black (ed.) American Society of Agronomy, Madison, WIMinter, D.L., Westerman, R.L., Johnson, G.V., Humidification for ICPAES analysis of salt extracts of soils (1990) Commun. Soil Sci. Plant Anal., 21, pp. 1587-1606Van Raij, B., Quaggio, J.A., Cantarella, H., Ferreira, M.E., Lopes, A.S., Bataglia, D.C., Extração e determinação da acidez dos solos (1987) Análise Quimica Do Solo Para Fins de Fertilidade, pp. 83-94. , Fundação Cargill, Campinas, BrazilReeve, N.G., Summer, M.E., Lime requirements of Natal Oxisols based on exchangeable aluminum (1970) Soil Sci. Soc. Am. Proc., 34, pp. 595-598Shuman, L.M., Duncan, R.R., Soil exchangeable cations and aluminum measured by ammonium chloride, potassium chloride and ammonium acetate (1990) Commun. Soil Sci. Plant Anal., 21, pp. 1217-1228Sposito, G., (1996) The Environmental Chemistry of Aluminum. 2nd Edition, , CRC Press, Inc., Boca Raton, FLStuanes, A.O., Ogner, G., Opem, M., Ammonium nitrate as extractant for soil exchangeable cations, exchangeable acidity and aluminum (1984) Commun. Soil Sci. Plant Anal., 15, pp. 773-778Trueby, P., Titration method for the simultaneous determination of hydrogen ions and aluminum in ammonium chloride soil extracts (1989) Z. Pflanzenernaher Bodenkd., 152, pp. 297-300