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OQ2.36\ severely eroded soils are still poten tially fertile. Most tillable soils would pro- duce abundantly with sufficient mois- ture, although the different soils have widely different characteristics that in- . fluence the land use, the crops to be grown on tilled land, and the methods of management and treatment that should be employed. Land-Capability Cillsses The facts obtained by the survey must be grouped and interpreted for most effective use in selecting and applying measures to control soil ero- sion, conserve wator, and manage the land. The soil types, the slopes, and the types and degrees of erosion are shown on the maps by brown boundary lines and symbols. Each set of these physieal conditions calls for a special set of practices and measures~for example, the treatment used on severely eroded hard lands (clay loams and loams)' differs greatly from that most suitable for slightly eroded sandy lands. Sig- nificant groupings of these physical factors aceording to the nature and intensity of the conservation and man- agement practices that are needed are called classes of land according to their capability for use, or, for brevity land- capability classes, They are shown on the maps in colors. Eight land-capability classes are recognized. in the entire Nation, but classes I, II, and V <).0 not occur in Baca County. The eight classes are: Suitable for cultivation with: 1. No special pract.ices. II. Simple practices. III. Intensive practices, IV. Limited use for cultivation. Not suitable for cultivation but suitable for permanent vegetation with: V, No special restrictions or special practices. VI. Moderate restrictions. VII. Severe restrictions. Not suitable for cultivation, grazing, or forestry: VIII. Not suitable for cultivation, graz- ing, or forestry, RELATION OF SOIL GROUPS, SLOPES, AND EROSION TO LAND CAPABILITY Although land-capability classes fur- nish a guide to the. intensity. and probable difficulty of eonservationor land-management practices that must be used, specific selection of practices for cropping, tillage, and grazing, must generally be made within each class according to the nature of the soil. Variations in moisture-holding capa- city, rate of infiltration, and suscepti- bility to erosion are closely related to texture, structure, and depth of the soil. No less important are the vari- ations in individual soils in their ability to release moisture to plants. Heavy-textured soils (clays, clay loams, and loams) generally are superior to the lighter textured sandy soils in their ability to retain moisture once it is stored. The infiltration rate or speed with which water enters the soil, however, is much lower on the heavy- textured soils than on the sandy ones. In dry weather moisture is released to the plant from the sandy soils more rapidly than from the heavier textured ones so, in general, crops grown on sandy soils make better use of the water that falls; that is, the sandy soils are not so droughty.. ,?pots of shallow soil, deposits of gravel or loose sand, stones on the surface, and exposed areas of caliche 3 further influence land use, since they add to the complexity of the soil pattern. For study of most of the character- istics that have an effect on land use, cropping possibilities, and conservation requirements the soils may be con- sidered in seven groups. and three subgroups. The seven groups are num- bered as in the bulletin Problem-area Groups of Land in the Southern Great Plains.' A more detailed description of the soil groups and of the soil types within each group is given on pages 42-50. They are listed in table 1 and on the back of each niap accompanying this bulletin. ~ Caliche is (I, local term for either indurated or unconsoli- dat.ed deposits of impure calcium carbonate. 4 FINNELL, H. H. PROBLEM-AREA GROUPS OF LAND IN THE SOUTHERN GREAT PLAINS, U. S. Dept, Agr. Unnumbered Pub. 40 pp., illUs. 1{139. Western and Southeastern Baca County Soil Conservation Districts, Colorado 3