Soil acidity is one of the major constraints of crop production in the Ethiopian highlands where precipitation is high enough to leach basic cations leaving the soil acidic. Liming is the major practice used to ameliorate the problem of soil acidity. Currently farmers use Ag lime in their fields to reduce soil acidity. However, the suitability of the existing methods of lime requirement (LR) has not yet being determined. Shoemaker-McLean-Pratt (SMP) single buffer, Adams-Evans buffer, Modified Mehlich buffer, titration with single addition of Ca (OH)2, and exchangeable aluminum methods were evaluated using the CaCO3 moist incubation method. The result revealed that the LR estimated by the buffer methods and titration highly correlated with the incubation LR since the correlation coefficient(r) was ≥ 0.98. The modified Mehlich buffer was better in predicting the LR on average, for target pH values of 5.5, 6.0, 6.5, 6.8 and 7.0 as r = 0.99 and as the standard error of estimate (Sy.x) 0.57, the minimum among the buffer methods. The modified Mehlich buffer should be calibrated further with the reference CaCO3 incubation using a set of soils and a calibration equation to calculate the lime requirement.
Key words: Acidity, lime requirement, calibration, buffer methods, incubation.
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