Physical Characteristics of the Soil Profile as Applied to Land Classification

Land classification, is, in its broadest sense, classification for use. In such a classification, we must take into consideration all those features, conditions and possibilities, appurtenant to the land, which may in any way contribute to the subsistence, comfort, or pleasure of human beings. The classification of land with this objective involves an examination and evaluation of geographic position, surface configuration, climate, soils, mineral deposits, vegetation, economic conditions, the character of the people inhabiting the land, their cultural development, their laws governing tenure and all other factors that influence or determine land use. A commission empowered to classify the land of any region and assign each tract to its most useful purpose,'should include in its personnel experts on cropping, grazing, forestry,mining, recreational facilities, and urban development. In the selection of land for any one of these purposes, the character of the soil is a factor of greater or less importance— of least importance in mining, greatest in the production of farm crops. The report of the soil scientist is, therefore, necessary, either to supplement the data of other specialists or to point out the dominating effect of the soil characteristics in the utilization of the land. The soil holds a peculiar place among the land resources. In itself, the soil is an almost useless substance. The value of any type of soil, and consequently its place in a land classification, depends almost entirely on its capability of producing useful plants. Not all soils are productive of useful plants, and not all characteristics of a soil promote the growth of a useful vegetation. So far as the characteristics of a soil determine the kind, amount and quality of the vegetation, they have significance in land classification. The importance of the soil and its characteristics, however, cannot be measured by the products of the land alone. Vegetation is the resultant of several forces, ofwhich the soil, although important, is not always dominant. The soil may not be able to impress its qualities on vegetation when"opposed by an adverse climate. In many cases, however, the soil is a determining or a limiting factor. Some plants will thrive only where the most favorable conditions exist in the soil; other plants have adapted themselves to tolerate chemical and physical conditions that would destroy less specialized plants. In some soils, the effects of a harmful characteristic are counteracted in part by other characteristics that are beneficial, or by special treatments in the course of cultivation. Many of the methods of management are designed to modify unfavorable physical characteristics of the soil. On the other hand, the responsiveness of a soil to management may be due to some favorable characteristic. Soils not inherently productive, as the sandy soils of the Atlantic Seaboard, are, by reason of physical character, responsive to fertilizers, and because of this quality, are highly valued for special crops. In this country, the most extensive investigations of the physical properties of the soil and nearly all studies of the soil profile are made in the field in the course of soil surveys. The soil surveyor is mainly concerned with the physical properties of the soil and their relation to plant growth, and his. soil categories are based, for the most part, on these properties. With the exception of a few simple qualitative tests, such as those made to determine the presence of lime or acidity, the soil surveyor does not employ the methods of the chemist. He appreciates the value of chemical analyses and requires them to supplement his findings, but his facilities for making analyses in the field are limited. An appraisal of the soil, however, based only on observations cf