Changes in particle-size distribution influenced by organic matter and mechanical or ultrasonic dispersion techniques

Abstract

Determination of particle-size distribution employing the most common methods is laborious and time-consuming. The objective of this study was to compare alternative analytical procedures adequate to classify soil texture of cropped soils. Eight Spanish topsoil samples selected according to their organic matter, CaCO3, and clay content, from representative agricultural Xerochrepts were tested. Differences in the methodologies were removal by hydrogen peroxide-treatment or no removal of organic matter and overnight mechanical shaking or ultrasonic physical dispersion. The pipette method was used for determination of particle fractions. Correlation for all the three particle sizes was found among the alternative procedures and the standard methodology (with removal of organic matter and mechanical shaking) and regression equations were developed (R2>0.96). Ultrasonic dispersion was found to be faster than mechanical shaking without significant (p<0.05) changes in reported results. The clay fraction was most affected by the use of modified techniques although the observed decrease did not change the soil textural class of any samples. Organic matter content produced more differences between the results, especially when no pretreatment for destruction of organic matter on samples with organic matter content higher than 2% was conducted. Except for the more organic samples, the advantages associated with no removal of organic matter and ultrasonic dispersion include decreasing the time and work, and allowing accurate measurements of agricultural soil samples.