680 
chayev with his pupils,° the most promi- 
nent of whom is Subertzev,® studied these 
questions for many years and arrived at 
what may be termed the most perfect and 
comprehensive scheme devised up to the 
present time. Theirs is a genetic system 
based upon climate, the formation of the 
soil, and the apparent properties. It was 
rather a statement of broad groups than 
the designation in systematic order of the 
factors, which give rise to agricultural dif- 
ferences in soils. 
The credit for definitely correlating the 
physical properties of the soil with its 
agricultural belongs chiefly to Whitney’ 
and his associates. By his work the tex- 
tural properties of the soil, through their 
influence on the moisture capacity and gen- 
eral climate of the soil, were shown to have 
a very determinate effect on the erop-pro- 
ducing power of the soil. The adaptation 
of natural vegetation and of domestic 
plants largely reflects these properties. 
Grass is shown to be generally identified 
with fine-textured soils, corn with loams 
and truck and other special crops with 
rather light sandy loams. 
The Federal Soil Survey—tn 1899, as 
chief of the United States Division of Soils, 
Whitney began the classification and map- 
ping of soils in the field according to their 
evident agricultural value. At first the 
physical properties were used almost ex- 
clusively as the means of separation. This 
survey work expanded and many men were 
employed in the field. Gradually the 
scheme of classification expanded, under 
the lash of necessity, keeping always to the 
fore the agricultural significance of each 
5 Tulaikov, N., ‘‘The Genetic Classification of 
Soils,’’ Jr. Agr. Sci., 3, No. 1, pp. 80-85, 1908. 
* Subertzev, N., Expt. Sta. Record, 12, 704-712, 
1900; 12, 807-818, 1901. 
™Whitney, M., U. S. Weather Bureau Bul. 4. 
Also Buls. S. C. Agr. Expt. Sta., Md. Agr. Exp. 
Sta. and U. S. Bureau of Soils. 
SCIENCE 
[N. S. Vou. XXXV. No. 905 
separation. Over four hundred thousand 
square miles were surveyed up to the be- 
ginning of 1911, distributed more or less 
in every state in the union. These surveys 
have proved their value and more than 
anything else have demonstrated the neces- 
sity of such work as a basis in general agri- 
cultural investigations and in education. 
They have also exemplified the necessity of 
arriving at definite principles for the 
classification of soils which in their dis- 
tribution have little relation to political 
boundaries. Following the lead of the 
federal government and as a supplement 
thereto, many of the states have taken up 
survey work, some independently and some 
in cooperation with the federal bureau. 
All this emphasizes the need for a common 
basis for work such as the committee on 
soil classification of the American Society 
of Agronomy is endeavoring to establish. 
While of great value and proceeding 
upon a broad basis of separation of soil 
types designed to represent their chief 
agricultural differences, on the one hand, 
the work has not always been as accurate 
as it might have been and, on the other 
hand, it has not been properly understood 
or appreciated because the factors which 
are used in the classification of soils have 
never been accurately stated. Individual 
survey men have been left very largely to 
absorb the scheme of separation from con- 
tact with the older men in the bureau and 
to work it out for themselves from pre- 
vious training and especially from experi- 
ence in the field. Apparently the factors 
which are used in the separation of soils 
are not always recognized and the group- 
ing of types is often not upon parallel lines 
or lines of equal significance. The proper- 
ties which determine differences in value 
have not been clearly perceived. The cor- 
ollary of inaccurate grouping is imaccu- 
rate boundaries of soil types. As an in- 
