Fractal analysis in the description of soil particle-size distribution under different land-use patterns in Southern Amazonas State, Brazil

Understanding the variability of soil properties is crucial to identify areas susceptible to physical degradation. The soil degradation is often determined by the current state of the soil structure, that is, the aggregate size distribution. Therefore, this article suggested evaluating aggregate sizes’ distribution by using the fractal theory. The goals were: (i) to calculate the fractal mass dimension of soil aggregates in areas under agroforestry, forestry, sugarcane, cassava and pasture in Southern Amazonas state, Brazil, showing correlations with soil properties; (ii) to compare the means of fractal dimension mass of the distribution of particle sizes on different soil under the different uses; and (iii) to investigate spatial variability of such fragmentation for each management system. Fragmentation was determined from fractal mass dimension. Aggregates were sampled within a depth range of 0.00 to 0.10 m, over a regular sample grid of 70 × 70 m, with georeferenced sample points, and regular spacing each 10 m, totaling 64 points per mesh. Higher mean values of fractal mass dimension were found in agroforestry use system and the lowest under native forest and pasture, with no statistical difference fractal mass dimension, when assessed in relation to the type and land use. The degree of fragmentation of soil aggregates was found to be influenced by the type of soil and strongly correlated with fine particles, higher in Red-Yellow Oxisols with better physical quality when compared with other areas. It showed a strong spatial dependence and the exponential model that got the best adjustment of the semivariogram. Key words: Soil physics, geostatistics, fractional dimension.