Towards a new and general method for decoding the soil texture from laser diffraction spectra

Abstract

Laser diffraction (LD) is a modern method for determining particle size distribution of soils and sediments. When deciphering particle size distribution, the area under the differential LD-spectrum is determined, limited by the vertical boundaries at the group edges according to the FAO-classification. In fact, there are no real vertical boundaries between the fractions of the particles, and the fractions themselves are distributed on a scale of size according to normal distribution. To eliminate the errors in the fractions content, deconvolution procedure for separating the original particle size distribution LD-spectrum is proposed. It resulted in a different share of the fractions compared to the common calculation method of the fractions content by FAO-classes. It is possible to detect new invisible fractions and, conversely, to exclude fractions defined within FAO vertical boundaries. In addition, the new indicator dispersion of LD-fractions (D) is proposed, which provides information on the property of individual fractions by particle size. Vertisols’ texture was heavier after deconvolution, especially in the Stavropol Vertisols. Vertisols had relatively low dispersion D < 0.7, which means relative homogeneity of LD-fractions. Northern Italy Andosols, however, had lighter texture after deconvolution. The number of LD-fractions was less than the number of FAO-fractions, while clay and fine sand (63–200 μm) LD-fractions were absent. It is likely due to the increase in LD-fractions dispersion, as evidenced by the high value of D (1.5).