Flf. Eltz et Ld. Norton, SURFACE-ROUGHNESS CHANGES AS AFFECTED BY RAINFALL EROSIVITY, TILLAGE,AND CANOPY COVER, Soil Science Society of America journal, 61(6), 1997, pp. 1746-1755
Surface roughness and canopy cover are important factors in preventing
soil erosion. There is limited information on how soil surface roughn
ess changes as a function of natural rainfall erosivity and canopy cov
er by plants. We hypothesized that canopy cover, tillage systems, and
cumulative rainfall erosivity (CRE) would have unique effects on rough
ness. We tested this hypothesis on a Miami silt loam soil (fine-silty,
mixed, mesic Typic Hapludalf) using a portable laser microtopographer
. Tillage treatments of conventional (moldboard plowing + disking), ch
isel plowing, and chisel plowing + dragging a chain produced three ini
tial roughness levels. Surface cover was none (fallow) or soybean [Gly
cine max (L.) Merr.]. Random roughness (RR), standard deviation (SD),
tortuosity (T), and fractal roughness functions, expressed by the frac
tal index (D) and the crossover length (l), were calculated from micro
topography data. Chisel tillage had the greatest initial values of sur
face roughness, followed by chisel + chain and conventional tillage, a
s measured by the l index. All indices but D generally decreased with
CRE. The RR and SD indices decreased quadratically with CRE, with decr
eases of 38 and 36%, respectively, from initial values after 200 units
of CRE, while the T and l indices decreased exponentially, with decre
ases of 40 and 60%, respectively, from initial values after 200 units
of CRE. Soybean cover lowered soil surface roughness 7% less than fall
ow, as measured by the l index. The l index was 50, 71, and 205% more
sensitive to changes in CRE than RR, SD, and T indices, respectively.
The fractal roughness functions, with D and l indices calculated, were
the best approaches to characterize surface roughness at small scales
, such as existing plant rows, mainly due to l index sensitivity to ch
anges in CRE.