290 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



an area lar^e enough to make classification on the soil basis possible. 

 Classifiers have fallen back on geology, climate, topography, or 

 native vegetation, all of which have their value, but such bases make 

 a classification indirect and approximate only. The Soil Survey has 

 now covered the eastern, central, and a large part of the far western 

 part of the country in sufficient detail to make the use of soil data in 

 land classification possible. 



During the calendar year of 1919 extensive studies were made of 

 most of that part of the (Jreat Plains about which our knowledge of 

 soil conditions is most deficient, for the purpose of accumulating 

 data to be used in the classification of the lands in this part 

 of our domain. The work is done in cooperation with the Office of 

 l arm Management, as the office in general charge of the project, with 

 various other bureaus of the Department of Agriculture, and with 

 the Geological Survey of the Department of the Interior. 



The study of the chemical composition of the virgin soils of the 

 United States in cooperation with the Division of Chemical Investi- 

 gations has progressed satisfactorily, considering the employment 

 difficulties encountered by all the chemical laboratories of the de- 

 partment. About 50 samples have been collected by the Soil Survey 

 during the year and complete analyses have been made of all of 

 them. 



GENERAL SOIL MAP OF THE UNITED STATES. 



The work on the general soil map of the United States for the Atlas 

 of American Agriculture is progressing satisfactorily and will be 

 finished before the close of the calendar year 1921. A draftsman has 

 been assigned to this project alone and has already compiled the 

 results of the Soil Survey work in most of the States east of the 100th 

 meridian. 



PREPARATION OF STATE SOIL MAPS. 



In some of the States the surveying of the soils is nearing comple- 

 tion, and it is time to make some provision for assembling the county 

 maps into more condensed State soil maps so that Ave may see at a 

 glance the soil resources of a State. This will necessitate the revision 

 of some of the older soil surveys and the bringing of the great mass 

 of data in the coimt}^ maps into one harmonious map. 



THE PERMANENCY OF THE SOIL AS AN AGRICULTURAL ASSET. 



Since the earliest historic times agricultural writers have speculated 

 as to the length of time the soil can be used to support the increasing 

 230i:)ulation of the world. This speculation still continues, and in 

 our coiintrj'^ there are well-informed people who believe that the 

 continued growing of crops depletes the soil to such an extent that 

 they predict the complete exhaustion of some of our most fertile soils 

 within a comparativelj^ few years unless enriched from time to time 

 with foreign material pound for pound for the plant food removed 

 by the crops. The Bureau of Soils does not hold this opinion, but 

 believes that the soil lias certain regenerative properties which will 

 permit its use for agriculture for an indefinite time, whether the 

 actual yield of crops shall decrease or increase during a term of 

 occupation of the land depending upon the knowledge and skill of 

 the cultivator. This question can be settled definitely only by a study 



