450 
THE TROPICAL AGRICULTURIST, [Jan. 1, 1903. 
The same remark very much appHes to 
" tea-growing on the Caucasus" : the Russian 
Government is not Hkely to throw away 
much money in trying to grow a product 
which can be bought of a better quality 
for a fraction of the price it will cost to 
produce. 
SOIL SURVEYS. 
Field Operations of the Division Soils, 1900. By 
Milton Whitney, Chief (U.S. Deparlmeat of Agrical- 
ture). Pp. 474 + a ease containing 24 maps. (Wash- 
ington, 1901.) 
Perhaps one of the greatest services which the 
scientific man can render to the agricultural com- 
munity in any country is the classification of the soils 
into certain types, defined by their chemical or physical 
properties, and the allocation of these types to their 
appropriate areas, so as to obtain a soil map of the 
district in question. 
Despite disturbing factors, certain types of soil per- 
sist over wide stretches of country aud are characterised 
by a general physical and chemical resemblance 
and also by a corresponding similarity in natural flora, 
appropriateness to particular crops and responsiveness 
to certain kinds of manure. The constancy of these 
soil types is the result of a common origin from 
the same kind of rock, and the difficulty lies less in 
recognising the type than in tracing its boundary line 
As a fundamental basis comes the geological survey, 
particularly the " drift " maps showing the superficial 
deposits due to running water, ice, &o., which, though 
of no great geological importance, are the origin of 
Boil survey of the soil proper. But for the purposes 
of a soil survey a little more than even a " drift " 
map is wanted; further subdivisibns must be introduced 
to show changes in soils on the same formation due 
to variations in the lifchological character of the forma- 
tion, or those due to the sorting action of water in 
the case of soils of transport. 
These variations, in fact soil classification generally 
must be based upon physical structure, must amplify 
and give exactitude to the practical man's division into 
clays, loams and sands ; the chemical properties of 
the soil may very concurrently, but are too much 
subject to casual change to serve as prime means of 
distinction. As an instance, the upper beds of the 
Lower Green sand in east and mid Kent give rise to 
rich loams, on whiah many fine hop and fruit planta- 
tions are situated ; further west the formation gradual- 
ly changes, until in west Surrey and Hampshire it is 
barren heath land the soil of which is alike wanting 
in the finer "clay ' particles, carbonate of lime and 
the soluble salts which go to feed the plant. Again, in 
the book under notice many examples will be found of 
two or more distaat soils of the same origin, eg. the 
maricopa soils (p. 302), described as consisting of 
"colluvial materials . . . largely granite : . . divided 
into four soils, depending upon the degree of com- 
minution of the rock." 
The volume before us represents a year's work of 
the Division of Boils of the United States Department 
of Agriculture in this particular direction of construc- 
ting a series of soil maps ; twenty-four of the maps 
are given on a scale of 1 inch to the mile, and show, 
by a system of colouring similar to that of a geological 
map, the type to which tho soil belongs. The ac- 
companying tftxt gives a mechanical analysis of 
the type soili.e its division into fractions each con- 
sisting of particles of a cei'tain size, aud in some 
caaes a chemical analysis, also such information 
collected on the spot as the distance to ground 
water, climatic features, chaiacteristio crops or natural 
flora and other local economic conditions. 
It was found, according to Mr. Whitney's prelimi- 
nary review, that it was quite possible to map these 
soil areas, independently of the geology of the area, or 
the exact chemical or physical character of the soil '> 
that the proper course was to construct maps in the field 
showing the area and distribution of the 
SOIL TYPES; 
to explain as fully as possible from geological consi- 
derations the origin of the soil and to leave the soil 
chemist and physicist study the differences. The fact 
is recognised that these chemical and physical pro- 
perties of soils are so complex and difficult that it may 
take many years to explain them through laboratory 
investigation ; but,pe,nding this complete investigation, 
the maps themselves will be of the utmost value to 
agriculturists in indicating the areas over which cer- 
tain soil conditions are found to prevail. . . . The 
recent successful growing of Sumatra tobacco on a 
certain soil in the Connecticut Valley is a very strik- 
ing instance of the possibilities growing out of the 
detailed soil survey in any given locality. 
The whole work is an excellent example of the 
thoroughness with which America carries out her 
State services ; the maps themselves are clear and 
distinct ; some of them, like the Saint Ana (California) 
sheet, represent a very complex distribution of soils, 
the survey of . which must have involved no light 
amount of field work, while the accompanying text 
is most liberally illustrated with analyses, sketch maps 
and sections, and photographs illustrative of scenery, 
crops or vegetation, the ease with which photographic 
illustrations are now produced beiag perhaps responsi- 
ble for the trivial nature of one or two of the objects 
selected. 
Several of the sections of the survey deal with that 
interesting factor in all arid or semi-arid areas, the 
existence of alkali soils and their extension under 
irrigation, which is, unfortunately, almost the only 
method of farming possible. 
Alkali is used in a generalised sense as indicating 
any predominance of soluble salts, generally sulphates 
and chlorides of sodium, magnesium and calcium, in 
the ground water, so that vegetation is destroyed or 
restricted to certain ''salt" plants, and on occasion 
the salts effloresce in a white powder on the surface. 
Sometimes carbonates of the alkali* are also present, 
which by their injurious action upon the texture 
of the soil and their solution of the humic acida 
give rise to " black alkali " spots, more dreaded 
even than the white. These " alkalis " probably 
represent nothing more than the normal products 
of the weatheriug of the fundamental rock minerals, 
but owing to the limited rainfall there is no per- 
colation through soil and subsoil, to wash every- 
thing 'Soluble into the rivers. Instead the salts 
remain in the subsoil, and irrigation, by raising 
the level of tho ground water, may easily bring 
the salts so near the surface that they rise in the 
capillary water to the surface and there are crys- 
tallised out. An instance of the damage due to care- 
less irrigation and the rise of the subsoil water is 
given in the report before us in the account of the 
Salt River Valley, Arizona. 
The phenomena of 
ALKALI SOILS 
and their increase through irrigation are neither 
new nor confined to the United States ; any 
arid climate where the products of weatheriug 
are not removed in the " country drainage " 
shows the same problem. Our irrigation engineers 
in India and Egypt are regularly confronted with 
the problem, for which thereis onlyone solution, under- 
drainage so that the cultivated soil may be washed 
from time to time, and carefal cultivation to minimise 
all evaporation from the soil except through the leaves 
of the crop. But though the 'alkali" problems are 
common in the old world, it has not been until the 
time of Hilgard Whitney and the present Division 
of Soils in the U S Dopartmant of Agricul'uce that 
we have had any real knowledge of their composition, 
or any study of the physical and chemical principles 
underlying the movement of the injurious material in 
the soil. 
