OCR Text |
Show substratum (G and D horizons); slope gradient and micro- relief; and kind and degree of past erosion. All the foregoing are not of equal importance in every soil. Furthermore, the importance of any one will de- pend upon the others with which it is found. The characteristics or properties in the list are those that must be considered in defining soil types or phases, or comparable classes and units of soils in making soil maps. Some are directly observable and can be used as criteria in field operations; others must be correlated with and inferred from directly observable characteristics. Investigations have shown that certain characteristics tend to be associated in soils and that it is, therefore, possible to define kinds of soils having relatively narrow ranges in the important characteristics or properties. After these relatively uniform kinds of soils have been defined and shown on. maps, they serve as a basis for accumulation and analyses of experience and research. Furthermore, the background of information is drawn upon in planning further investigations, in future interpretations of research, and in the planning and development of various programs. Basic soils data are collected by a number of Federal agencies and by several of the States. The Bureau of Plant Industry, Soils, and Agricultural Engineering col- lects soils data and publishes such data in the form of soils maps and related descriptive material. The Soil Conservation Service also collects and publishes soils data on land capability maps. Likewise, the Bureau of Recla- mation collects such data for use in the classification of irrigable lands. Soils data axe also needed for engineering purposes, such as for roads, levees, dams, and the like. At present, not all of the requisite data useful to engineers are shown on soils maps or are considered in accompanying descriptions. This should be remedied. It can be done by obtaining certain added information on soil characteristics, such as shearing strength, consolidation, compaction, and plas- ticity. Such information, if obtained concurrently with other phases, would broaden the usefulness of the soils maps and furnish information needed in planning and construction. Greater coordination between agencies and groups in- terested in soils is needed. Such coordination should lead to better understanding of soils problems, better inte- gration, and gxeater usefulness of various soil data. Status of Soils Data The soil surveys made by the Bureau of Plant Industry, Soils, and Agricultural Engineering, in cooperation with the State agric-ultural experimental stations, cover approxi- mately 650 million acres, of which approximately one- third consists of early works in need of revisions. In these detailed surveys the mapping units are soil types and phases. Most of such soil maps that have been produced are on a scale of 1 : 62,500. The areas covered by these surveys are indicated on figure 34. The soils data collected by the Soil Conservation Service as a part of so»il conservation survey cover approximately 322 million acr-es. Areas covered by such maps are shown on figure 35. Soils data which have been collected for irrigability surveys by the Bureau of Reclamation cover approximately 39 million acres and the areas are indicated on figure 38. It would be helpful in many areas if soil mapping were done by quadrangles, permitting soils to be superimposed on basic topography and geology. Although there are great gaps in the knowledge of soils, the greatest deficiency exists in the soil information for forest and range lands. This is particularly true on the public lands. This lack of adequate soils information for the public lands is resulting in heavy losses to public property. There are other deficiencies with respect to basic soils data. These are both physical and chemical. For ex- ample, some 15,000 infiltration tests have been made on perhaps 100 soil types throughout the country. Such in- formation needs to be extended to all the important soils as a basis for runoff and other determinations. Similarly, erodibility is not known for many important soils although land classifications and land management practices should be based on such information. Knowledge of the true depth of root penetration and of the march of soil moisture throughout the root zone is imperfect. A great storehouse of information in soils has been collected, as a result of the activities of many investigators. Soils have been under study by Federal and State agencies, experiment stations, and laboratories for many years. Despite all this study, there are still great gaps in our knowledge, which can only be closed by continued and further research. A whole new field of effort has been opened to the soils scientists by recent atomic developments. Isotopes are beginning to permit study of such matters as the passage of water through the soil, the rate at which vegetation takes water into its system, and the rate at which water is transpired. Such studies will improve underr' ¦-.-, " -^ of the physical, chemical, and biological properties of soil and the water relations between soils and plants. Information about the soils of this country should be obtained over the Nation as a whole without waiting in each place until the imminence of som«- \. ~ogram demands it. This information will help in solving many problems, no one of which would justify an independent investigation, and at the same time avoid the necessity of obtaining such facts every time a new problem arises. There is need for proper balance among the segments of a program of soil investigations. Field mapping pro- vides a part of the information on which soil classification can be based. Physical, chemical, and mineralogical analyses and careful morphological studies also provide a part. Investigations that disclose the behavior of soils under various treatments and uses ultimately make the classification of maximum usefulness. Recommendations All interested Federal and State agencies should co- operate in collecting basic information on soils. Agencies should, wherever practical, contribute toward completing basic soil studies. Nation-wide soil classification and mapping should be accelerated on the basis of an orderly and periodic pro- gramming. It should be completed in 20 years. The proper content and degree of detail needed in soils activities should be subject to periodic review and adjust- ment to procure the widest possible service consistent with reasonable cost. 360 |