The hazards of nutritional deficiencies for plants, and even for animals, can be predicted from soil maps if the relationships of deficiencies to soils have been established. In recent years, important relationships have been worked out between many soils and their deficiencies of such elements as copper, boron, manganese, molybdenum, iron, cobalt, chromium, selenium, and zinc. The relationships between soils and deficiencies of phosphorus, potassium, nitrogen, magnesium, and sulfur are widely known. Relationships of soils to some toxic chemical elements have also been established. By no means have all of the important soils been characterized, especially for the trace elements.
More research is needed.
The relative importance of soil varies widely among the many uses of land. Where the soil is a factor of production, as in farming, ranching, or forestry, its capacity to produce and its requirements for production are elements of land value. Soil surveys provide information in terms of soil qualities that bear directly on land value for many different purposes. These interpretations are used most often, however, in assessing farmland for taxation and equalization, in appraising land for loans, and in guiding land buyers. The soil is only one of the elements that must be considered for appraisal of land value within the local, economic, and institutional environment of an area.