Land-Use Conversion Changes the Multifractal Features of Particle-Size Distribution on the Loess Plateau of China

Analyzing the dynamics of soil particle-size distributions (PSDs), soil nutrients, and erodibility are very important for understanding the changes of soil structure and quality after long-term land-use conversion. We applied multifractal Rényi spectra (D(q)) and singularity spectra (f(α)) to characterize PSDs 35 years after conversions from cropland to shrubland with Caragana microphylla (shrubland I), shrubland with Hippophae rhamnoides (shrubland II), forested land, and grassland on the Loess Plateau of China. Multifractal parameters (capacity dimension (D(0)), entropy dimension (D(1)), D(1)/D(0), correlation dimension (D(2)), and Hölder exponent of order zero (α(0))) were used to analyze the changes of PSDs. D(q) and f(α) characterized the PSDs well and sensitively represented the changes in PSDs after conversion. All types of land-use conversion significantly improved the properties of the topsoil (0–10 cm), but the effect of shrubland I and even forested land decreased with depth. All types of land-use conversion significantly increased D(1) and D(2) in the topsoil, and D(1) and D(2) in the 10–50 cm layers of shrubland II, forested land, and grassland and D(1) in the 50–100 cm layers of shrubland II were significantly higher relative to the control. Both D(1) and D(2) were positively correlated with the contents of soil nutrients and fine particles and were negatively correlated with soil erosion, indicating that D(1) and D(2) were potential indices for quantifying changes in soil properties and erosion. In conclusion, all types of land-use conversion significantly improved the conditions of the topsoil, but conversion from cropland to shrubland II, forested land, and grassland, especially shrubland II and grassland, were more effective for improving soil conditions in deeper layers.