Regionalized soil roughness indices

The soil roughness at the field level is an easy visually perceptible notion, but difficult to describe numerically. The objective of this paper is to propose a method to establish quantitative and descriptive soil roughness indices. A measurement system was developed using a laptop-computer and a laser cell. The elevation data are measured on the ground along a square array. They are treated with geostatistics methods. For a given direction, the semi-variogram shape, depending on the distance, is always comparable with ground relief, and reflects in a positive way the variations of this relief. New quantitative indices are proposed. They are derived from semi-variogram and they characterize the roughness in both vertical and horizontal planes. For the five plots the main results are: on crusted soil without soil tillage, the semi-variogram is nearly flat in isohypsic direction and has a parabolic shape in the slope direction. On an isohypsic bank the semi-variogram presents a shape with a hole effect upright to the bank. For an oriented knife soil tillage, the semi-variogram is bimodal, with a hollow effect in the axis perpendicular to the vine-rows. With a not clearly oriented soil tillage, the semi-variograms in all directions have a practically similar feature with a sill. The semi-variogram corresponding to the direction transversal to a gutter has a bell-slope. q 1998 Elsevier Science B.V. All rights reserved.