26 BULLETIN 995, U. S. DEPAKTMENT OF AGRICTILTTJRE. 
there must be more or less alkali dissolved in the water. As this 
water rises to the surface of the soil it brings with it the salts held 
in solution. After the water evaporates from the surface of the 
soil the alkali remains, and it may eventually accumulate to such an 
extent that crop production is greatly reduced or rendered entirely 
impossible. This condition is a limiting factor in the production 
of sugar beets as well as other crops in certain portions of the sugar- 
beet area. The sugar beet is one of the most alkali resistant of our 
farm crops, but even with this plant the limit of endurance is some- 
times reached or exceeded, and beet growing becomes unprofitable. 
Alkali in the seed bed is especially troublesome, since the young 
plants are very tender and therefore susceptible to this and other 
adverse conditions. If the beet plants are well started before the 
alkali accumulates in the surface soil, much less damage will be done, 
as the subsequent growth of the plants is less affected by the same 
amount of alkali. The alkalinity of a soil may be reduced by the use 
of irrigation water, provided the irrigating water is comparatively 
free from alkali and a satisfactory drainage system has been 
established. 
SOIL FERTILITY. 
Elements of plant growth. — By fertility is meant the ability of 
the soil to produce a good crop. The difference between a rich soil 
and a fertile soil should be kept in mind — that is, a soil is rich if it 
contains a considerable quantity of each of the elements required by 
the plant in the process of growth. Unless, however, these elements 
are available to the plant and the physical conditions of the soil are 
such as to promote plant growth, the soil cannot be said to be fer- 
tile. If a single element required by the plant, though present, is 
not soluble, this condition will render the soil infertile. In order 
that an element may be available to the plant, it must be soluble, and 
it must dissolve rapidly enough to supply the plant with that par- 
ticular element as rapidly as the plant requires it. Certain elements 
are always available when present; other elements must he acted 
upon by certain substances under certain conditions in order to 
become available or soluble. It is apparent, therefore, that fertility 
is one of the limiting factors in the production of sugar -beets as well 
as of other crops. 
The sugar beet requires the same elements of plant food that are 
required by other field crops, but in slightly different proportions : 
for example, a 10-ton crop of sugar beets (which is approximately 
the average yield for the United States) will require about 30 pounds 
of nitrogen. 11 pounds of phosphoric acid, and 71 pounds of potash : 
a wheat crop, yielding 20 bushels per acre, will require 41 pounds of 
nitrogen, about 13 pounds of phosphoric acid, and 17 pounds of 
