E. Perfect et al., SOIL AND TILLAGE EFFECTS ON THE CHARACTERISTIC SIZE AND SHAPE OF AGGREGATES, Soil Science Society of America journal, 61(5), 1997, pp. 1459-1465
Measures of aggregate size and shape are needed in models to predict s
oil erosion, seed bed density, tensile strength, and solute diffusion.
We hypothesized that size (i.e., equivalent cubic length L-c = [l(1)(
l(2)/root 2)(l(3)/root 3)](1/3), where l(1), l(2), and l(3) are the sh
ortest, intermediate, and longest axial lengths, respectively) and sha
pe (i.e., aspect ratios, l(1)/l(3) and l(2)/l(3)) vary with soil type
and tillage treatment. Caliper measurements of l(1), l(2), and l(3) we
re made on 1800 aggregates from three sieved fractions (4-8, 8-16, and
16-31.5 mm) of a plowed, plowed plus dished, and no-till Maury silt l
oam (fine, mixed, mesic Typic Paleudalf) and a no-till Karnak silty cl
ay (fine, montmorillonitic, nonacid, mesic Vertic Haplaquept). Overall
means for l(1)/l(3) (0.57) and l(2)/l(3) (0.78) were close to those f
or a cube (0.58 and 0.82, respectively). The mean l(1)/l(3) for Karnak
was 18% lower than the corresponding value for no-till Maury. The L-c
was lognormally distributed. The mean log(10)(L-c) increased from 0.6
7 in the smallest fraction to 1.19 in the largest fraction. Soil effec
ts on log(10)(L-c) 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
log(10)(L-c) 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 dis
hed Maury, respectively). The equation L-c = x(1)(m/m(m))(1/3), where
x(1) is lower sieve aperture, m is aggregate mass, and m(m) is modal m
ass, explained 96% of the variation in L-c. This equation can be used
to predict aggregate size from sieve aperture size and measurements of
aggregate mass.