Comparison and conversion of particle size distribution measurements for black soil using two types of laser particle sizers

Particle size data for black soil, measured using a Malvern laser particle size analyzer, were compared with those obtained using a Beckman laser particle size analyzer, and both results were benchmarked against data obtained using the pipette method. The study aimed to establish formulas for interconverting laser diffraction data to those from the pipette method, and for interconverting data obtained using the two laser particle size analyzers.

A total of 147 black soil samples were tested. Among them, 33 surface soil samples collected from different regions of the black soil area were analyzed using the laser particle size analyzers and the pipette method to establish formulas for interconversion of the data from the laser diffraction and pipette methods and for interconversion of the data from the two laser particle size analyzers. Another 114 black soil samples collected from the Hebei small watershed were only tested using the two laser particle size analyzers. The effectiveness of the formulas for interconversion of the data measured using the two particle size analyzers was evaluated. The data from the two laser particle size analyzers for the 114 samples from the small watershed were converted to align with those from the pipette method using the aforementioned conversion formulas for soil texture classification.

For the 33 samples from the black soil area, the clay content (< 0.002 mm) measured by the pipette method was significantly higher than that measured by the laser diffraction method, but there was a significant correlation between the two methods (p < 0.01). The sand content measured by the pipette method was higher than that measured using the Beckman particle size analyzer but lower than that measured using the Malvern particle size analyzer. However, corresponding conversion formulas could also be derived for each method (p < 0.01). For the black soil samples from the small watershed evaluated using the two laser particle size analyzers, the difference in the clay content was relatively small, with an average absolute error of 2.5%. However, the absolute average errors in the silt and sand content were > 10%. After conversion, the difference decreased, with an average absolute error of 1.8% for the clay content, 3.9% and 6.3% for the silt content in the International System and the American System, respectively, and 5.1% and 7.4% for the sand content in the International System and the American System, respectively. After converting the data from the two laser particle size analyzers to align with those from the pipette method, the values could be consistently used for soil texture classification of the small watershed samples, with a consistency rate of 93.0% for the International System. However, for texture classification using the American System, the consistency rate was only 58.8%.

Therefore, there are significant differences in the raw values obtained with the two particle size analyzers, making the data unsuitable for direct comparison. However, there is a highly significant correlation between the two (p < 0.01). The conversion formulas established using samples from black soil regions can considerably reduce the differences, providing a better basis for soil texture classification in the international system for black soil.