Improved Estimation of the Soil Particle-size Distribution from Textural Data

Abstract

It is possible to estimate the particle-size distribution using textural data with a proposed model by other investigators. The proposed model was based on clay, silt and one sand subclass (i.e. very fine plus fine sand fractions with an extreme radius of 125 μm). This model is easy to use, but requires values of very fine plus fine sand fractions. As for most conditions, only the value of all sand subclasses is available, it is proposed using radius of 999 μm (near radius of 1000 μm corresponded to the extreme value of the radius for sand particle in the United State Department of Agriculture system) instead of 125 μm for the extreme value of fine sand fraction for 50 different soils with various textures. Forty-four soils had silt content less than 60% and six soils had silt content more than 60%. The results indicated that for all soils, prediction of particle-size distribution was much better when using a radius of 999 μm then using a radius of 125 μm. Furthermore, for improving the results of predicted particle-size distribution using the radius of 999 μm, the ratios between the measured and predicted particle-size distribution for each radius of particle-size (1, 1·5, 2·5, 5, 10, 15, 20, 25, 35, 50, 75, 100, 150, 200, 300, 400, 500, 750 and 1000 μm) were used for the soils with less and more than 60% silt content, separately. The results showed that the values of correction coefficients may be used for only the radii less than 25 μm (clay and silt contents). The results indicated that using the correction coefficients for 44 soils with less than 60% silt content tended to better or as well estimation of particle-size distribution for 30 soils (i.e. 68·2%), and tended to give a much better estimation of particle-size distribution in all six soils with more than 60% silt content.