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.
Part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Mississippi State Univ. Contribution from the Mississippi Agric. For. Exp. Stn., Mississippi State, MS, and the USDA Natl. Sedimentation Lab., Oxford, MS. Journal no. 6470.