Evaluation Of Lime Requirement Methods For Acidic Soil: A Case Study From Nedjo District, West Wollega Zone, Ethiopia

Abstract

Soil acidity is the most serious challenges to agricultural production and productivity worldwide in general, and developing countries in particular. Liming is a common agricultural practice worldwide, which is used for increasing the productivity of acidic soils. Liming reduces aluminum toxicity, increases the soil pH up to values where the availability of Al decreases; and the bioavailability of essential nutrients, such as phosphorous is enhanced. In this study, three buffer methods for determining the lime requirements, namely, the Shoemaker - McLean - Pratt single buffer (SMP-SB); Shoemaker - McLean - Pratt double buffer (SMP-DB) and new Woodruff buffer methods were evaluated. These buffer methods were evaluated using Ca(OH)2-titration to a pH of 6.5; and CaCO3-incubation to a pH of 6.0 and 5.5 as a reference pH because they are reliable and were often used as a calibration for buffer methods. In this study a total of 24 soil samples representing the major agricultural acid soils in Nedjo district were considered. The lime requirement needed for adjusting the pH to 6.5, 6.0 and 5.5 were correlated with the amounts of exchangeable aluminum (r = 0.80), exchangeable acidity (r = 0.82), Organic carbon (r= -70) and soil pH (r= -0.97). The study revealed that the SMP-DB is the best method for determining the lime requirement for the Nedjo district acid soils. The SMP-DB method gave the highest correlation coefficient values (r=0.98) with the reference pH, the least variations from the ideal lines. The sensitivity of the SMP-DB method was comparable for soils of high (>5.88 t/ha) and low (<5.88 t/ha) lime requirements, while the sensitivity of SMP-SB and New Woodruff methods were poor for soils of low and high lime requirements. Pot experiment in lath-house the highest plant height, spike length and biomass were obtained at pH 5.99 and 6.14 in Vertic Luvisols and Rhodic Nitisols, respectively; while the biomass yield of wheat was declining at pH levels beyond these. Since it might not be necessary to lime these soils to pH levels higher than 6.0. Hence, to ameliorate the soil over there, the SMP-DB method is recommended.