Soil surface roughness, the configuration of the soil surface, affects
infiltration, runoff velocities, erosion, and plant establishment
and growth. One difficult aspect of studying surface roughness is
that parameters describing roughness vary spatially. Eight roughness
parameters were identified as possible indices of soil surface
roughness. They were maximum peak height, maximum depression
depth, peak frequency, the ratio of peak frequency to peak height,
microrelief index (the area per unit transect length between the measured
surface profile and the least-squares regression line through
the measured elevations of the transect), the ratio of microrelief
index to peak height, the ratio of microrelief index to peak frequency,
and lastly the product of the microrelief index and peak
frequency (the MIF parameter). The objective of the study was to
determine the spatial variation of the eight indices using a semivariogram
analysis. An automated, noncontact profiler was used to
obtain surface profiles along transects 5 cm apart of 1-m by 1-m
plots after a cultivation and a simulated rainfall application at each
of three different stages of soybean [Glycine max (L.)] development.
For each cultivation, surface profiles were obtained on bare plots
before rainfall and on adjacent vegetated plots after rainfall. None
of the eight indices commonly showed spatial dependence. When a
roughness parameter was spatially dependent, however, its semivariogram
usually was spherical, linear with a nugget constant, or
exhibited a hole effect. Across all plots on which they were found
to be spatially dependent, the indices exhibited zones of influence
averaging from 15 to 20 cm.
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