Wind erosion roughness index response to observation spacing and measurement distance

Abstract

The cumulative shelter angle distribution (CSAD) is a physically-based roughness index that can be used to estimate the amount of soil surface impacted by saltating sand grains which produce wind erosion. But little is known of how observation spacing and other measurement factors affect CSAD estimates. This study was designed to determine the effect of observation spacing and range of influence (distances within which calculations are made) on CSAD parameters. Soil surface roughness measurements were made using a laser profile meter on a chiselled sandy clay loam soil after seven levels of simulated precipitation applied at four intensities. In this study, the different rainfall amounts and intensities were used only to create different roughness levels. Calculations were made on replicated plots using five observation spacings ranging from 4 to 48 mm in directions parallel and perpendicular to the tillage direction and ranges of influence of 150, 300, 400 and 600 mm. Calculations of roughness using different observation spacings and range of influence produced significant differences ( P≤0.05) in CSAD estimates. Each observation spacing tested was different from all others. Ranges of influence of 300 mm or more produced similar CSAD parameter values. Estimates of the fraction of the soil surface susceptible to wind erosion decreased as the observation spacing decreased. When measured parallel to tillage, 92% of the soil surface was susceptible to abrasion when the observation spacing was 48 mm but 54% of the surface was susceptible when the observation spacing was 6 mm, suggesting roughness elements as small as 6 mm offer protection to the soil surface if they are nonerodible.