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This article in SSSAJ

  1. Vol. 61 No. 5, p. 1459-1465
    Received: July 17, 1996

    * Corresponding author(s): eperfect@ca.uky.edu
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Soil and Tillage Effects on the Characteristic Size and Shape of Aggregates

  1. E. Perfect ,
  2. Q. Zhai and
  3. R. L. Blevins
  1. Department of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091



Measures of aggregate size and shape are needed in models to predict soil erosion, seed bed density, tensile strength, and solute diffusion. We hypothesized that size (i.e., equivalent cubic length Lc = [l1(l2l√2)(l3l√3)]1/3, where l1, l2, and l3 are the shortest, intermediate, and longest axial lengths, respectively) and shape (i.e., aspect ratios, l1/l3 and l2/l3) vary with soil type and tillage treatment. Caliper measurements of l1, l2, and l3 were made on 1800 aggregates from three sieved fractions (4–8, 8–16, and 16–31.5 mm) of a plowed, plowed plus disked, and no-till Maury silt loam (fine, mixed, mesic Typic Paleudalf) and a no-till Karnak silty clay (fine, montmorillonitic, nonacid, mesic Vertic Haplaquept). Overall means for l1/l3 (0.57) and l2/l3 (0.78) were close to those for a cube (0.58 and 0.82, respectively). The mean l1/l3 for Karnak was 18% lower than the corresponding value for no-till Maury. The Lc was lognormally distributed. The mean log10(Lc) increased from 0.67 in the smallest fraction to 1.19 in the largest fraction. Soil effects on log10(Lc) were most evident in the 8- to 16-mm fraction (1.01 for Karnak compared with 0.93 for no-till Maury). Tillage effects on log10(Lc) were most evident in the 4- to 8-mm fraction (0.68 for no-till Maury compared with 0.66 and 0.65 for plowed and plowed plus disked Maury, respectively). The equation Lc = xl(m/mm)1/3, where xl is lower sieve aperture, m is aggregate mass, and mm is modal mass, explained 96% of the variation in Lc. This equation can be used to predict aggregate size from sieve aperture size and measurements of aggregate mass.

Kentucky Agric. Exp. Stn. Contribution no. 96-06-113.

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