A System for Correlation of Land Forms and Covers with Soil Classification

This country is most fortunate, in having an established scheme of soil classification which has been in effect and has been applied on actual surveys throughout all parts of the country during a considerable number of years. It is also fortunate in that the scheme is flexible and applicable to all degrees of detail and to all scales of field mapping. It is but logical, therefore, that this system of soil classification should be incorporated in any scheme for evaluating the dominant factors which affect land use, whether for purposes of land classification or for the direct utilitarian purpose of developing soil conservation measures. When the Soil Erosion Service (later the Soil Conservation Service) launched the first soil conservation projects, it was necessary to establish principles and to develop procedures to attain the desired objectives. At the very outset, it was adopted as a cardinal principle of the organization that soil conservation plans should be predicated upon an inventory of those factors which are of dominant importance in land use. Since these conservation plans had to be made for each field of each farm within the project area and had to conform to variations in conditions which •would affect the conservation plans even within a field, it was essential that the inventory of the dominant factors affecting conservation be shown in place on a detailed map of each farm. Thus, each area delineated on the farm maps, whether an entire field or parts of a field, received an evaluation of each of the four factors shown by the survey. While the immediate objective of the survey was directly utilitarian in that soil conservation plans were developed at once for each farm in accordance with the findings of the survey, the surveys furnished also a valuable accumulation of data which were rendered more valuable for analyses of the physical factors, influencing land use because they were shown in detail and in place. Thus, when the survey of any project area ±s completed, whether 25,000 or 200,000 'acres, the conditions of any one factor can be summarized for the area as a whole, or can be analyzed in relationship to each other, or to all other factors. The analyses of these conditions can in turn be correlated with farm management surveys or other farm studies. The factors which are considered to be of dominant'importance in soil conservation, and hence, the ones shown by the inventory, listed in the order in which they will be discussed hereafter, are four in number, as follows: (l) soil type; (2) present land use or ground cover; (3) slope; and (4) character and degree of erosion. Since these four factors are shown for each field, and usually for different parts of one field, it is necessary to delineate upon a large-scale map, each field and each area within which any one of the four factors varies. This entails the construction of large-scale accurate base maps. It has been found that the most satisfactory base maps upon which to show all of the detail desired are aerial survey pic— tures, particularly since recent photographs show much of the information desired, such as cover, drainage, roads, buildings, fences fences, gullies, and, to a certain extent, other erosion conditions, such as severe sheet or wind erosion. There has been marked development in aerial'photography in the last few years. Mr. Marshall Wright, in charge of Cartography in the Soil Conservation Service, has delivered a paper here, telling of the progress made in that field. Costs have been reduced materially, and the