The Effects of Bulk Density and Water Potential on Multifractal Characteristics of Soil Penetration Resistance Microprofiles Measured on Disturbed Soil Samples

Abstract

Soil compaction may interact with available soil water and aeration porosity, affecting root and crop growth. Most commonly, soil compaction status is assessed by penetration resistance (PR) tests. The Least Limiting Water Range (LLWR) is an indicator of soil structural quality that appraises the simultaneous effects of water availability, aeration, and PR on plant growth. High resolution PR microprofiles are commonly acquired for LLWR assessment. Multifractal analysis of these microprofiles provides a new opportunity to investigate highly localized heterogeneity at the scale of small soil cores. The objectives of this work were to characterize the scaling properties of depth‐dependent PR microprofiles using multifractal analyses and to explore the effects of soil bulk density and water potential on the degree of multifractality of these PR data series. Disturbed soil cores from a clayey Oxisol (Rhodic Hapludox) were assayed at seven different levels of bulk density (ρb) in the range of 1.00–1.60 kg dm−3 and at six different matric potentials (ψ) from −6 to −1500 kPa, yielding 42 treatments. Each treatment was replicated three times and three PR microprofiles were recorded per soil core, so that 378 PR data series were analyzed. Singularity and Rényi spectra revealed the multifractal behavior of PR microprofiles, and the multifractal approach provided considerable detailed information on their depth‐dependent structure. Rényi spectra and singularity spectra of PR microprofiles, and specially the branches accounting for the most negative statistical moments, depended on ρb and ψ. Effects of bulk density on multifractal parameters were modeled by a linear equation, while water potential effects were modeled by an exponential relationship to log (−ψ). Increasing ρb gradually reduced the degree of multifractality. Increased dryness increased the degree of multifractality, notably near the wilting point, while higher water contents near field capacity showed no significant effects on the degree of multifractality.