Asian Journal of Plant and Soil Sciences

Soil acidity can restrict nutrient availability and crop performance in inland valley swamp soils, while soil pH alone does not adequately indicate the quantity of lime required to reach a target pHThis study was conducted to determine the lime requirement (LR) and lime-buffering capacity (LBC) of selected inland valley swamp (IVS) soils in Moyamba District, Sierra Leone, using a calcium chloride/calcium hydroxide titration procedure, and to identify contrasting soils for subsequent lime-response calibration. A laboratory analytical survey of 51 IVS soils was conducted, comprising triplicate titration determinations, descriptive classification of LR and LBC, replicate precision assessment, bivariate LR-LBC evaluation, exploratory clustering, and spatial interpretation. Soil samples were collected from 51 IVS sites in Moyamba District and analysed at the Njala University Quality Control Laboratory, Sierra Leone. Composite topsoil samples (0-20 cm) were air-dried, sieved to 2 mm, and titrated in 0.01 M CaCl₂. A 20 g soil subsample was equilibrated with 20 mL CaCl₂, after which 3 mL increments of 0.1 M Ca(OH)₂ were added with shaking and repeated pH measurements until pH 6.5 was attained. Added Ca(OH)₂ was converted to CaCO₃ equivalent, LBC was derived from the neutralising requirement per unit pH change, and LR was expressed as t CaCO₃ ha^-1. Determinations were performed in triplicate. Titration-derived LR ranged from approximately 1.40 to 5.57 t CaCO₃ ha^-1. Forty-seven soils (92.2%) were classified as medium LR (2.0-4.0 t ha^-1), while two soils each (3.9%) were low (<2.0 t ha^-1) and high (>4.0 t ha^-1). LBC also varied substantially: 36 soils (70.6%) were medium (520-720 mg CaCO₃ kg^-1 soil pH unit^-1), eight (15.7%) were low, and seven (13.7%) were high. LR increased overall with LBC, but the relationship was dispersed, confirming that buffering capacity alone did not determine LR. Replicate precision was satisfactory for most soils, with most LR coefficients of variation below about 10%. Nyalahun (3.73 t CaCO₃ ha^-1) and Njala Junction (5.57 t CaCO₃ ha^-1) represented contrasting medium- and high-LR soils, respectively. The IVS soils showed substantial heterogeneity in both acidity-neutralisation demand and resistance to pH change. Soil pH alone is therefore inadequate for district-wide lime prescription. A soil-specific titration approach that integrates initial acidity, target pH, and buffering capacity provides a defensible basis for selecting lime rates, but the laboratory estimates should be calibrated under incubation and field conditions before recommendations are made to farmers.