Submitted to: Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/27/2006
Publication Date: 9/1/2006
Citation: Arriaga, F.J., Lowery, B., Mays, M.D. 2006. A fast method for determining soil particle size distribution using a laser instrument. Soil Science. 17(9):663-674. Interpretive Summary: Soil particle size distribution is an important characteristic that affects many important soil physical and chemical properties. Traditional methods for determining soil particle size distribution are laborious and require a considerable amount of time. A simple procedure was developed to analyze soil particle size distribution with a commercially available laser-light scattering instrument. The time needed to analyze a soil sample was reduced dramatically when compared to traditional methods of soil particle size characterization. Reproducibility between different operators was good and agreement with other accepted methods was satisfactory. However, because of inherent assumptions in any particular procedure, it is not recommended to compare results from different methods. Although this technique does not have a perfect agreement with traditional techniques, it does provide data rapidly and for the full range of soil particle sizes. This can be extremely valuable in situations that require a large number of samples, such as mapping soil spatial variability over a landscape or soil profiles.
Technical Abstract: The pipette method has been designated as the standard method for determining soil particle size distribution (PSD), even though obtained values may not necessarily represent the actual PSD of a given sample because of assumptions made in this procedure. The pipette method is a lengthy procedure, requires significant operator input, and potentially there can be considerable differences between operators. However, if conducted properly it can be a precise procedure. Light scattering methods for determining PSD are quick and, unlike the pipette, provide continuous PSD information without additional operator input. A simple procedure for sample handling and treatment was developed for determining soil PSD with a commercially available laser-light diffraction instrument that measures particles with a diameter between 2,000 and 0.04 m. Time required to analyze a sample was 10 min. A combination of chemical and physical soil dispersion was found to be convenient and effective. Reproducibility between different operators was good, with standard deviations ranging from 2 to 36 kg kg-1, indicating small differences. Correlations between the pipette and light scattering instrument for sand was good (R2 = 0.75), but it decreased for silt and clay (R2 = 0.64 and 0.15, respectively). A similar trend was observed when the hydrometer was compared to the pipette method. Because of inherent assumptions in any particular procedure, it is not recommended to compare results from different methods. The laser-light scattering technique does not have a perfect agreement with classical techniques, but it does provide data rapidly and for the full range of particle sizes. This can be extremely valuable for mapping spatial variability of soil PSD over a landscape or profile.