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United States Department of Agriculture

Agricultural Research Service

Title: Rapid Particle Size Analyses Using Laser Diffraction

Author
item ZOBECK, TEDDY

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2004
Publication Date: November 2, 2004
Citation: Zobeck, T.M. 2004. Rapid particle size analyses using laser diffraction. Applied Engineering in Agriculture. 20(5): 633-639.

Interpretive Summary: There are many methods to measure the amounts of different sizes of particles in soils. This information about the particles is needed to classify the soils into a particular texture class and predict how a soil will behave under different management practices. Current standard methods are time consuming and labor intensive. Recent advances in technology have produced new laser based electronic devices capable of rapidly performing a particle size analyses. This paper compares results obtained using a laser based instrument with results obtained using standard methods. Forty three soils were used in the study. The results obtained using the laser device were almost identical to the results obtained using standard methods. We found better comparisons when soils with pH less than 8.0 were analyzed separately from soils with a pH greater than or equal to 8.0. Although we found excellent correlations of the methods in this test, caution should be used when applying this technique. Calibration equations comparing the techniques should be restricted to soils with similar mineralogy and source of sediment (parent material).

Technical Abstract: Soil particle size analyses (PSA) are needed to relate soil texture to soil performance or behavior. Standard analyses of dry soils usually include dispersion of the soils followed by particle size determination by a variety of time consuming methods. Clay and silt sized particles are usually measured by sedimentation using a hydrometer or pipette method. Sands are then measured by sieving. Recent advances in laser diffraction technology have led to the production of devices specifically designed to rapidly measure the particle distribution of dispersed particles. This stud, compares the PSAs of 43 soil samples collected from the Southern High Plains of Texas, measured by the pipette method and sieving, to results obtained using a laser diffraction particle size analyzer (LDPSA). No pretreatment to remove organic matter or salts was used in this study. The LDPSA requires about 300 mg soil sample and overnight dispersion while shaking in a sodium hexametaphosphate (soap) solution. Each sample was analyzed in about ten minutes, including device clean up. The correlation of the laser analyses with pipette analyses varied by particle size and mineralogy. Better correlations were obtained when non calcareous soils were separated from calcareous soils. Regression analyses relating laser and pipette methods of non calcareous soils yielded coefficients of determinations of 0.97, 0.99, and 0.99 for the <2 m , <50 m, and <100 m fractions, respectively. Use of the laser particle size analyzer greatly reduced the time and labor required for soil PSAs. Since a relatively small sample size is required, care must be taken to ensure a representative sample is selected for analysis

Last Modified: 9/10/2014
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