Rapid tests for estimating lime requirements of some soils of São Paulo

Abstract

Five rapid laboratory tests for lime requirements (LR) were calibrated against a method in which soils were incubated with CaCO₃ until a pH equilibrium was attained. The Woodruff and SMP methods, which estimate the LR from the pH depression of buffer solutions in soil-buffer suspensions, satisfactorily estimated the LR for pH control. The SMP buffer, as used in Ohio, gave values that were about double the true values, but was satisfactory when the amount of soil in the suspension was reduced to one-half the original amount. The LR values as measured by the acidity extracted by Co(OAc)₂ at pH 7 and as estimated from base saturation-pH curves were highly correlated with LR to pH 5.5, 6.0 and 6.5 by incubation. A method based on acidity extracted by KCI and on (Ca+Mg) supply was satisfactory in the neutralization of exchangeable AI and in supplying (Ca+Mg), but gave low correlation with LR for pH control.