Fractal distribution of mass from the millimeter- to decimeter-scale in two soils under native and restored tallgrass prairie

详细信息    查看全文

• 作者：Daniel R. Hirmas ; Daniel Gim¨¦nez ; V ; ana Subroy ; Brian F. Platt
• 关键词：Three-dimensional (3D) scanning ; Fractal model of water retention ; Soil bulk density
• 刊名：Geoderma
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：207-208
• 期：Complete
• 页码：121-130
• 全文大小：1464 K

文摘

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 (500-1000 cm³) 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 1.1 cm. We found a strong relationship between d_b and the combination of organic carbon and silt + clay content (R² = 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.