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TERRACING FOR SOIL AND WATER CONSERVATION
requires a recognition of the soils and slopes upon which crop pro- duction can be carried on without increasing soil losses beyond per- missible limits. The erosion-control program would be greatly simplified if all farming operations could be restricted to relatively noinerodible slopes and the more erodible land returned to its natural vegetative cover. Under present economic conditions, however, it is necessary to produce crops on land slopes that will require certain control measures if cropping is to be continued successfully. Terracing, supported by necessary cropping practices, is primarily applicable on sloping lands that must be used for crops and on which less expensive conservation measures will not provide adequate ero- sion control. Too often terracing is represented as an alternative to a permanent vegetative cover of grasses or trees. This misconception of use has caused much confusion and misunderstanding in the gen- FIGURE 5.-Once gully erosion has advanced to this stage it practically prohibits cultiva- tion of a field and greatly reduces its value for any agricultural use. rally accepted application of these control measures. Terracing should not be considered for land that can be placed or retained under permanent vegetative cover, except possibly where terraces may be required for moisture conservation or diversion of water for gully control or as an aid in establishing a satisfactory cover of permanent vegetation. Neither can terracing be economically justified on lands that can be adequately protected by proper tillage and agronomic measures such as contour tillage, crop rotations, and strip cropping. These measures alone may provide sufficient protection where rela- tively low rainfall intensities and high soil infiltration rates are en- countered, where erosion-resistant soils or relatively flat slopes pre- vail, and where profitable rotations can be introduced that will provide an erosion-resistant cover during a large part of the rotation cycle, particularly during the rainy seasons. But where erodible soils, long slopes, and high rainfall intensities are encountered and where a large percentage of erosion-permitting crops must be used 4773 0 -~8
