Testing the integral suspension pressure method for soil particle size analysis across a range of soil organic matter contents

Abstract

Particle-size distribution is a critical part of soil description, which is commonly measured using pipette and hydrometer methods. However, a recently developed technique, called the integral suspension pressure method, allows for the measurement of continuous particle-size distribution based on Stokes’ law. The objective of this study was to evaluate the appli- cability of the integral suspension pressure method for measuring particle-size distribution, as an alternative to the standard hydrom- eter procedure. The integral suspension pressure method was tested by using a soil dataset with a wide range of organic matter contents (0.22-12.0%). Forty-nine samples were analysed with a hydrom- eter after organic matter removal and the results were compared with those obtained using the integral suspension pressure method. Through comparing the integral suspension pressure and hydrom- eter measurements, root mean square error values of 8.9, 8.1, and 11.9% were observed for sand, silt, and clay, respectively. The clay fraction was underestimated throughout the entire range of meas- urements. Conversely, the silt content was overestimated over the whole range of measurements, especially in samples with more than 36% silt. When compared to the hydrometer method, integral suspension pressure integral suspension pressure exhibited a ten- dency to misclassify the soil texture of clay loam samples but was accurate for sandy loams.