## Abstract

Fractal models that describe the distribution of aggregate mass and the hierarchical organization of soil structure at scales relevant to hydrological processes have been tested only over a small range of aggregate sizes. The objectives of this work were to extend to the decimeter-scale the range of aggregate diameters used in mass-volume investigations, to examine the ability of a fractal model to describe the mass-volume relationship, and to assess the variability of fractal parameters obtained from individual clods sampled within the same horizon. Soils at a native prairie (NP) and a restored prairie (RP) at a formerly cultivated field site in northeastern Kansas were studied. Six clods (500-1000cm^{3}) sampled from each of two soil horizons at the NP (A and Btss1) and RP sites (Ap and Btss1) were sequentially broken and volume measured with a combination of a multistripe laser triangulation scanner and a displacement technique using two immiscible liquids. Volumes were converted to diameters and normalized by individual aggregate/ped roundness, paired with their respective masses and fit with a power law expression to obtain D_{m} (fractal dimension of mass) and k_{m} (the mass of an aggregate of unit diameter). Except for the RP Btss1 horizon, the fits demonstrated two domains separated at a breakpoint, d_{b}, with values between 0.8 and 1.1cm. We found a strong relationship between d_{b} and the combination of organic carbon and silt+clay content (R^{2}=0.95, P<0.01) suggesting that these properties interact to control aggregation in aggregates with diameters smaller than d_{b}. D_{m}-values for the Btss1 and A horizons were not fractal (D_{m}=3) for small aggregates and fractal with values between 2.79 and 2.89 for large aggregates. For the RP Ap horizon, D_{m} was 2.51 for the small and ~3 for the large aggregates, likely due to high concentrations of roots and organic carbon observed in this horizon. Variation of D_{m} and k_{m} within any given horizon was large and comparable to the variation of similar values obtained from water retention from a variety of soils of contrasting textures found in other studies, suggesting that a more thorough understanding of the horizon-scale variability of these parameters is needed in order to appropriately apply fractal models of water retention. Our results confirm that fractal models provide a theoretical framework to describe soil structure, but they should be developed from data spanning several orders of magnitude and tested critically.

Original language | English |
---|---|

Pages (from-to) | 121-130 |

Number of pages | 10 |

Journal | Geoderma |

Volume | 207-208 |

Issue number | 1 |

DOIs | |

Publication status | Published - 1 Oct 2013 |

Externally published | Yes |