Multifractal analysis of soil particle size distribution to evaluate the effects of gypsum on the quality of sodic soils

摘要

Soil particle size distribution (PSD) essentially determines the soil's physical characteristics, including aggregate stability and porosity. Evaluating the PSD of sodic soils altered by reclamation is beneficial to the development of strategies for addressing land degradation. However, it remains unclear how to extract the features of PSD of sodic soils sensitively under gypsum reclamation. In this study, a total of 108 soil samples collected from a reclaimed sodic field were measured for PSD along with other soil properties, including hydraulic conductivity. Almost all the reclaimed sodic soil was measured to be silt loam, which was not obviously different from their original texture. The concentration, uniformity and symmetry of PSD of sodic soils have been quantified by fractal and multifractal geometry methods, in which the multifractal method provided more parameters than the fractal method to characterize the features of PSD more sensitively. The multifractal method offering predictive parameters (i.e., D-1, D-2, alpha(min) and alpha(0)-alpha(min)) was able to significantly (p < 0.05) differentiate the features of PSD. The multifractal results indicated that the heterogeneity of PSD at 0-60-cm depth was increased by reclamation, whereas the major particle size (silt) in these sodic soils decreased, and the combined treatment (i.e., using flue gas desulphurization [FGD] gypsum plus leaching water) created the most heterogeneous PSD. The redistribution of soil particle size caused by reclamation treatments resulted in the improvement of soil physical and chemical properties, showing increased soil aggregate diameter, raised total porosity, enhanced saturated hydraulic conductivity and decreased pH. The findings of this study bring a new opportunity to evaluate the effects of gypsum on the quality of sodic soils from the PSD perspective, which also provides a reference for evaluation of reclamation of other poor soils.