Quantifying Coarse Fragments in Soil Samples Using a Digital Camera

Abstract

We developed a novel method using image analysis to quantify the content and shape characteristics of coarse fragments in an Alfisol developed from loess over outwash. A total of 45 soil samples (about 600–1000 g each) were collected at 10-cm depth interval from 0 to 150-cm deep at three transects in the profile. The coarse fragments were separated from the soil fine-earth particles and photographed in the laboratory. The images were processed using ImageJ processing software that provides total count, total area, and mean circularity of each sample, as well as shape characteristics (circularity, aspect ratio, roundness, and solidity) of each coarse fragment. The amount of coarse fragments (coarse fragments, total count/mass, and total area/mass) varied with depth and was highest in the 2C1 and BC horizons where the soil was developed from coarse glacial outwash and a mixing of coarse outwash and loess. The coarse fragments content was lower in the loess and fine glacial outwash horizons. Approximately 9.6% of coarse fragments in weight or 14.5% by count moved from the glacial outwash layer into the loess layer (Ap and Bt horizons). The shape characteristics showed large variations at 50–110 cm depth where the soil was developed from coarse glacial outwash and a mixing of coarse outwash and loess. The mean circularity, roundness, and solidity of the coarse fragments at the topsoil were larger than those at the 50-110 cm, indicating that rounder stones tend to move faster than irregularly shaped stones during the frost heaving. This method provides a robust, fast and quantitative way to estimate the distribution and the shape characteristics of coarse fragments in a soil sample that can be applied to help better understand soil formation.