RELATING PLANT CANOPY CHARACTERISTICS TO SOIL TRANSPORT CAPACITY BY WIND

Federal legislation mandates that wind erosion soil losses be kept to a ''Tolerable'' limit to maintain eligibility for federal farm program s on highly erodible land. Therefore, much interest has been generated in devising wind erosion models that accurately determine the potenti al erosion from a given site and also evaluate the effectiveness of an y control measure. These models require mathematical relationships bet ween surface properties and the transport capacity of the wind. Such r elationships are available for soil surface roughness and plant residu es, but not for growing crops. Our objective was to establish these re lationships for growing crops. We developed a theoretical approach tha t accounts for the effect of stem area, leaf area, and canopy cover of growing crops on the soil loss ratio, threshold velocity, and transpo rt capacity. The predictive ability of the theory was tested using pub lished data sets from growing plants tested in a wind tunnel. Measured soil loss ratios were highly correlated to predicted values (r(Z) = 0 .99, P = 0.001). The results showed that plant area index and canopy c over are highly correlated with reduction in the transport capacity of the wind and, therefore, serve as indicators of the soil protection a fforded by growing plants. A plant area index of 0.02 and a canopy cov er of 4% reduced the transport capacity of a 16 m s(-1) wind by 50%. T his method for determining the protective ability of a combination of growing plants and standing residue will improve predictive capabiliti es of wind erosion models for more diverse farm management conditions.