Acidity control in Latosols under long-term pastures in the Cerrado region, Brazil

International audienceHigh acidity and aluminium saturation are among the main limiting factors for crop production in tropical soils. The aim of this work was to measure the acidity of Latosols under pastures in the Brazilian Cerrado and to assess the influence of clay mineralogy as a controlling parameter of soil acidity. Topsoils (n = 73, 0-0.2m depth) of Latosols developed on different parent materials were sampled in two sub-regions of the Cerrado region. The main chemical characteristics were determined by standard procedures, and kaolinite and gibbsite contents were determined by dissolution with sulfuric acid and thermogravimetric analyses. The exchangeable concentrations of calcium (Ca), magnesium (Mg), and potassium (K) varied considerably among soil samples, with ranges of 0-13.9 cmol(c) kg(-1) (mean +/- standard deviation 1.77 +/- 1.91 cmol(c) kg(-1)) for Ca; 0.2-3.2 cmol(c) kg(-1) (1.13 +/- 0.68 cmol(c) kg(-1)) for Mg; and 0-1.0 cmol(c) kg(-1) (0.24 +/- 0.24 cmol(c) kg(-1)) for K. The mean concentration of exchangeable aluminium (Al) was 0.55 +/- 0.61 cmol(c) kg(-1) (range 0-2.3 cmol(c) kg(-1)). The content of kaolinite (282 +/- 96 g kg(-1)) was higher than of gibbsite (106 +/- 77 g kg(-1)). The amount of exchangeable Al and Al saturation rate varied according to the mineralogy of the clay fraction of the soils. The content of exchangeable Al3+ remained low when gibbsite was the predominant mineral, whereas it increased with kaolinite content. The ratio kaolinite/(kaolinite + gibbsite) could be used as a useful indicator of the sensitivity of soils affected by acidity and Al toxicity