Abstract:
This study tests the validity of the Sur and Kukal modified hydrometer method for particle size analysis on eight Ghanaian soils of varying texture. The method assumes that hydrometer readings at any time could be predicted from an exponential equation provided that two important parameters are known: the 4.5-min hydrometer reading (R4.5) and the exponent (B). In a series of sedimentation experiments conducted on each soil in this study, 11 hydrometer readings were taken between 40 s and 8 h. Some of these data were used to determine the value of the parameters R4.5 and the exponent B. The B values for the light textured soils were within the range of 4.2 × 10 -3 to 9.7 × 10-3 and were comparatively lower than those for the heavy textured soils (1.0 × 10-2 to 1.5 × 10-2). In addition, the R4.5 values were much lower for the light textured soils than for the heavy textured soils. Using these parameter values in the Sur and Kukal's equation enabled the prediction of the hydrometer readings at different times during the sedimentation process. The predicted 8-h hydrometer reading also was used to calculate the percent clay. A comparison between the observed and predicted hydrometer readings was satisfactory. The predicted percent clay also agreed very well with that observed for all soils (R2 = 0.96). It is concluded that the Sur and Kukal method indeed simplifies the determination procedure and yields acceptable results for a wide range of Ghanaian soils.