Abstract: 【Objective】 The aim of the study are to analyze the impact of long-term fertilization on the heterogeneity of the soil particle-size distribution of red soils, to investigate the mechanisms of soil development process affected by different fertilization strategies and to explore the ways to promote sustainable development of agriculture while maintaining soil quality. 【Method】 A laser particle size analyzer was used to measure the particle size distribution of the soil samples. The soils were collected from the top 20 cm soil depth in four treatments with a wheat-maize rotation system at two time points in the long-term fertilization experiment on red soil in Qiyang, Hunan province in 1990 and 2012. The treatments include long-term continuously non-fertilizer (CK), chemical fertilizer (NPK), NPK plus manure (NPKM), and manure alone (M). The changes of the multi-fractal parameters of particle size distribution were analysed by the box dimensions method. Furthermore, the correlation analysis between the multi-fractal parameter, soil particle and organic matter was also carried out. 【Result】 The results showed that the multi-fractal parameter represented the heterogeneity of soil particle-size distribution much sensitively and accurately and it was significantly correlated to the contents of soil clay or silt particle and soil organic matter. Generalized dimensions (D(q＜0)) were more sensitive than that of D(q＞0) in the range of -10≤q≤10, indicating that the scaling property of D(q) in the sparse range was less than that in the dense range. Compared to the values of Ds from initial soil samples, long-term fertilization did not significantly influence the capacity dimension (D0) or information dimension (D1), but significantly increased the correlation dimension D2 (0.864-0.883), D1/D0 (0.921-0.932), the singular strength (1.129-1.177) and the singular spectrum width of (1.966-2.707). 【Conclusion】 Long-term application of manure with or without chemical fertilizer significantly improved the local intensity of soil particle-size distribution, promoted soil refinement and accelerated the development of soil inhomogeneity under the similar soil-forming conditions, cropping system and agricultural management. The multi-fractal parameter was much more sensitive to the changes of soil particle-size distribution, which could provide a technical support for the research on precision of soil particle size distribution.

Key words: multifractal characterization , particle-size distribution , long-term fertilization , red soil , laser particle-size analysis