Acidity and chemical properties of Brazilian soils

In soils of tropical climate regions the high acidity and the presence of exchangeable aluminum (Al), associated to low fertility, are the main restrainting factors for agricultural production. A laboratory experiment was conducted using 26 soils of different Brazilian regions, to investigate soil acidity components, giving emphasis to Al and their relations with chemical properties. The pH correlated positively with P, Ca, Mg, K, BS, CEC and V% values, and negatively with Al saturation. The Al was the predominant exchangeable cation in 32% of the soils with pH below 5.6. The KCl titratable H represents the hydroxi-Al(OH)x complex with low stability and the Wolf-Morgan extracted Al corresponds to the exchangeable + non-exchangeable Al species. The Al and low stability hydroxi-Al decreased quickly with increasing pH up to 5.5. The nonexchangeable Al increased up to pH 4.5, then decreased to pH 5.5 and had a small increment from 7.0 to 7.5.