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United States Department of Agriculture

Agricultural Research Service

Title: Wind Erosion Roughness Index Response to Observation Spacing and Measurement Distance

Authors
item Zobeck, Teddy
item Popham, Thomas

Submitted to: Soil Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 1997
Publication Date: N/A

Interpretive Summary: The soil surface configuration or roughness can protect the soil surface from the effects of wind. Rough soil surfaces are far less susceptible to wind erosion than smooth surfaces. ARS scientists are investigating ways to mathematically describe the soil surface and predict how various management and climatic factors affect the surface roughness. The wind erosion roughness index can be used to estimate the amount of soil surface subjected to abrasion during dust storms. This study describes how changing the spacing of height elevation readings and other factors affect the computation of a wind erosion roughness index and demonstrated the importance of oriented tillage marks created during tillage. For example, when the amount of soil surface subjected to abrasion was computed relative to tillage direction, relatively low tillage ridges (90 mm high) protected over 20% more of the soil surface in the direction perpendicular to the tillage ridges than in the direction parallel to tillage. Caution must be used when computing this wind erosion roughness index because observation spacing affects the result obtained. We recommend collecting measurements of 5 mm intervals over a 1-meter square area.

Technical 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 zone of influence (areas within which calculations are made) on CSAD parameters. Soil surface roughness measurements were made using a laser profile meter on a chiseled 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 zones of influence (ZOI) of 150, 300, 400, and 600 mm. Calculations of roughness using different observation spacings and ZOI produced significant differences (P less than or equal to 0.05)in CSAD estimates. Each observation spacing tested was different from all others. Zones of influence of 300 mm or more produced similar CSAD values. Estimates of the fraction of the soil surface susceptible to wind erosion, a roughness index of practical value that can be estimated using the CSAD, 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 4 mm.

Last Modified: 8/30/2014
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