Lime requirement determination methods on acid neutralisation efficiency under selected acidic soils of the Ethiopian highlands

An incubation experiment was conducted with the objective of identifying the best lime requirement (LR) determination method(s) and calibrating them for estimating the LR of selected acid soils in Ethiopia. The methods include modified Mehlich buffer (MMB), modified Adams-Evans buffer (MAEB), and exchangeable acidity (EA). The soils were collected from 10 acid-prone districts in the country. The treatments included in the study were 0, 50, 100, 150, and 200% of the lime (CaCO3) rate estimated by each method and incubated for 3 months using 500 g soil. The results showed that the LR determined by EA was very low, whereas LR estimated by MAEB was too high and brought the pH above the target values of 6.0 and 6.5. The average LR of all the study soils for the pH target values of 6.0 and 6.5 were 7.9 t ha(-1) and 11.7 t ha(-1) as estimated by MMB; 21.5 t ha(-1) and 28.9 t ha(-1 )as estimated by MAEB, and 3.5 t ha(-1) by EA method. MMB estimated 100% of the LR that gave a pH value ranging from 5.84 - 6.25 with an average value of 6.04, fitting the target pH of 6.0. The correlation coefficient for LR determined between MMB and incubation was 0.87 as compared to 0.85 for MAEB and incubation. The comparison among the study soils also indicated that the LR of Luvisols was higher than that of Nitisols attributed to their inherent chemical properties and thus high buffering capacities. A stepwise multiple regression analysis showed that 98.5% of the variation in the LR is accounted for by pH, exchangeable Al, and OM, collectively, with F (3,6) = 200.8; P < 0.001. Therefore, it is concluded that MMB is the best method for estimating the actual lime required for reclaiming acidic soils of the study locations and areas having similar conditions.