Page 125 - Soil Degradation, Conservation and Remediation

4.6 Wind Erosion Control Measures 113

Fig. 4.3 Cover crop of clover in an orchard in California (Photo courtesy of USDA-NRCS)

vegetation and anchoring the soil with roots. Green manuring cover crops are tilled
into the ground in the spring, at least 1 month before planting the next crop. This
provides additional nutrients to the crop, as the cover crop decomposes. The Dust
Bowl (a period of severe dust storms causing major ecological and agricultural
damage to American and Canadian prairie lands in the 1930s) has taught farmers
the importance of planting cover crops for the control of wind erosion. Legumes,
such as soybean or clover, are common choices for cover crops. Their vegetation
reduces ground air pressure, and their roots hold the soil in place, in addition to their
contribution to fixation of nitrogen (Fig. 4.3).

4.6.3 Ridging and Surface Roughening

Chepil and Milne (1941) observed that the initial intensity of drifting was always
much less over a ridged than a smooth surface. Ridging cultivated soils (Fig. 4.4)
reduces the severity of drifting. However, ridging highly erosive dune materials was
less effective because the ridges disappeared rapidly. Experimental data showed
that the rate of flow varied inversely with surface roughness. It is influenced by
ridge spacing and ridge height, and it is defined relative to a 1:4 ridge height to ridge
spacing ratio. A soil ridge roughness of 6 cm reduces wind erosion 50 %. Fryrear
(1984) found a greater reduction in wind erosion by ridging; erosion remained
relatively constant as ridge roughness increased beyond 11 cm. Lyles and Tatarko
(1982) found that chiseling of growing winter wheat on a silty clay soil increased
greatly non-erodible surface aggregates without influencing grain yields. Listers,
chisels, cultivators, one-way disks with two or three disks removed at intervals, and