Fractal characterization of soil particle-size distribution under different land-use patterns in the Yellow River Delta Wetland in China

Purpose Soil particle-size distribution (PSD) is an important soil physical property. Single-and multi-fractal models are increasingly used to characterize soil properties and may provide additional information. The Yellow River Delta is one of the best representative examples of river ecosystem wetlands in the world. In this area, different land resource development patterns strongly influence soil structure and fertility. Here, the single-and multi-fractal characterizations of soil PSD were determined based on fractal theory, and the correlations between PSD and soil organic matter (SOM) across different land-use patterns were studied. Materials and methods The study site was located in a typical area of the Yellow River Delta Wetland in Shandong Province in China. The tested soil samples were obtained from areas with four different land-use patterns, including integrated Robinia pseudoacacia and grass cover land (RPG), well-covered European and American poplar forestland (EAP), cropland used for growing cotton (COT), and waste grassland (WAG). Soil samples were air-dried and passed through a 2-mm screen. Based on the international system of soil size fraction, the soil PSD was described according to the percentages of clay, silt, and sand. The clay, silt, and sand fractions were determined using a laser particle size analyzer. The fractal characterizations of soil PSD were determined using the single-and multi-fractal methods. Results and discussion The single-fractal dimension (D) of the different land-use patterns varied greatly (between 2.4657 and 2.6789). The D values of the RPG and EAP were the greatest, which corresponded to the soils with the greatest silt content and the lowest sand content. In contrast, the D value of the WAG was the smallest, which corresponded with the lowest clay content and the greatest sand content. These results indicated that D was directly proportional to clay content and inversely proportional to sand content. The multi-fractal parameters of the soil PSD, capacity dimension (D-0), information dimension (D-1), and information dimension/capacity dimension (D-1/D-0), followed a regular trend due to different land-use patterns. These parameters decreased in the following order: RPG>EAP>COT>WAG. In addition, the PSD of the RPG and EAP varied widely and was more heterogeneous than the PSD of the COT and WAG. Furthermore, the single-and multi-fractal parameters were significantly correlated with SOM. Conclusions Our findings indicated that the single-and multifractal parameters adequately described the scaling properties of the soil PSD and the influences of soil structure and soil nutrients for the different land-use patterns in the Yellow River Delta Wetland of China.