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Comparison of Laboratory pH Buffer Methods for Predicting Lime Requirement for Acidic Soils of Eastern Botswana

Abstract The suitability of pH buffer methods that determine lime requirement (L.R.) of acid soils of the eastern region of Botswana has not been determined, and the soil physiochemical properties that influence L.R. are not known. As a result, a number of laboratory pH buffer methods for determining L.R. were evaluated by using acid soils from that region. The methods evaluated were the Yuan double buffer (Yuan–DB) method, Shoemaker, McLean, and Pratt double, and single buffer (SMP–DB and SMP–SB) methods, and the Adams, and Evans single buffer (AE–SB) method. The evaluation was based on the ability of the methods to predict the actual L.R. to pH 6.5 determined by the soil–CaCO3–moist–incubation (SCMI) method. The incubation, physiochemical properties, and L.R. by laboratory pH buffer methods were determined in triplicates. All the pH buffer methods were (P < 0.001) significantly correlated (0.79 < r < 0.94) with the SCMI method. The performance was in the order of Yuan–DB method > SMP–DB method > SMP–SB method > AE–SB. However, the SMP–SB has been recommended for routine analysis of soils of eastern Botswana, because it is simple and rapid. The relationship between SCMI method actual L.R. and the physiochemical properties (0.55 < r < 0.71) reveals that the buffer capacity, organic carbon, exchangeable acidity, and extractable aluminum are the most important soil properties influencing L.R. of soils in eastern Botswana.