Walkley‐Black Digestion Efficiency and Relationship to Loss on Ignition for Selected Sierra Leone Soils

Abstract

AbstractTen top soils sampled from six physiographic positions in the Njala Survey Area of Sierra Leone, West Africa, varied in organic carbon content from 1.02 to 7.82% and in clay content from 22 to 65%. Walkley‐Black oxidation efficlency ranged from 93 to 100% and averaged 97%, using Wet Combustion as standard. Organic matter in these tropical soils is apparently in forms easily oxidized by the sulphuric acid‐dichromate digestion.Simple correlation between organic carbon (C) and loss on ignition (L.O.I.) was very strong, r = 0.997; partial correlations showed that when organic C was held constant, 31% of the variation in L.O.I. was associated with clay content variation, and when clay content was held constant, 98% of the variation in L.O.I. was associated with organic C.Ignition loss of organic C was closely predicted by the linear relationship y = 0.505 x − 0.094, where x = % organic C. Prediction error (about 0.5%) was proportionately greater at lower levels of ignition loss.