Content area
Full text
When soils are smooth, bare, and exposed to erosive winds, a portion of the surface soil may be detached and transported by wind. The quantity of soil moved by wind will depend on the shear force generated by the wind and the susceptibility of the soil surface to erosion. If erodible soil particles are present and the threshold velocity of the wind is above that required to move the potential erodible soil particles, erosion will occur. Erodible soils may be protected with crop residues, wind barriers, soil amendments, soil ridge roughness or stable soil aggregates creating ridge roughness with tillage machines, establishing table borders or strips of vegetation.
In the late 1930s, wind erosion research was concerned with identifying methods of expressing the influence of soils on wind erosion. To determine the wind erodible fraction of soils, surface soil samples were sieved with flat sieves to separate the sample into erodible and nonerodible fractions (1). The susceptibility of the soil to movement by wind, "its erosiveness," was determined using a wind tunnel. Soil particles larger than 0.8 mm were stable in winds of 5.8 m/s at a height of 0.3 m and were considered nonerodible. Based on the sieving and wind tunnel tests, Chepil (1) concluded that dry soil clod structure could be used to develop an index of wind erosiveness of cultivated soils. However, flat sieves were subject to overloading, operator technique, plugging, and inconsistent results but have been used to determine wind erodibility in the fall and spring (10).
The first rotary sieve separated a dry soil sample into seven size fractions (4). The main advantages of rotary sieves over flat sieves were (a) consistency of results, (b) reduced operator error, (c) consistent results regardless of sample size, (d) less breakdown of soil clods, (e) eliminates clogging, and (f) suitability for resieving of same sample to determine mechanical stability (3). A rapid rotary sieve (7) was designed to determine erodible fraction of soils in about one fifth the time of a compact rotary sieve. The rapid rotary sieve also provides a relative measure of aggregate stability, but it does not separate the sample according to particle size. The two-sieve method was developed to simplify the determination of erodible fraction, but the compact rotary...