REPORT OF THE SECRETARY. 151 



stmctible asset of the Nation, which can be vastly improved by better 

 and intensiA'e methods or which can be temporarily impaired by 

 wrong usage. 



This conclusion was reached through a mineralogical study of soils 

 and rocks, the study of the solubility of soil minerals and of the 

 composition of the soil solution, the study of the profound changes 

 taking place in the soil constantly through the mixing of soil grains 

 by erosion, winds, and internal movements, and in the soil con- 

 stituents through the action of percolating and capillary waters, the 

 stud)'' of the increasing yield of farm crops during the 40 years for 

 which records have been kept in this country, a study of the much 

 larger increases in yields on the older soils of Europe during the 

 past 300 years, and by a comparison of the chemical composition of 

 the relatively new soils of this country and the. relatively older 

 agricultural soils of Europe. 



SOIL SURVEYS. 



Admitting that the productivity of our many important soils 

 depends in the long run upon the knowledge and skill of our people 

 in handling each type according to its specific needs, the importance 

 and significance of the bureau's work in the classification and map- 

 ping of soils can be more fully appreciated. 



During the last 12 years soil surveys have been made of 622,595 

 square miles, or an area practically as large as the combined areas 

 of Germany, France, Great Britain, Ireland, and Italy. In this 

 work the soils are classified according to their origin and constitu- 

 tion, and the reports discuss their characteristics, their principal 

 tillage requirements, and their crop adaptations. Omitting the 

 sparsely settled Eocky Mountain region, the Northwest Intermoun- 

 tain region, the arid Southwest, and the Great Basin, the survey 

 has covered 29.2 per cent of the land surface of the United States, 

 giving a complete classification of the soils, showing their area and 

 distribution within the limits of the surveys, and indicating in a 

 general way the localities outside of the areas surveyed where the 

 different soil types may be expected to be found. 



ADAPTATION OF SOILS. 



During the progress of this work and through supplemental in- 

 vestigations, the special adaptation of many of these types of soils 

 to crops has been worked out, and we have definitel)' established the 

 cause of many failures in farming to be the attempt to produce crops 

 on soils to which they are not adapted and upon which a high degree 

 of commercuil success can not be expected. 



