THE BEET-SUGAR INDUSTRY IN 1920. 27 
potash ; a corn crop, yielding 40 bushels of ears to the acre, will 
require 56 pounds of nitrogen, 21 pounds of phosphoric acid, and 
23 pounds of potash ; clover yielding 2 tons of ha}^ per acre requires 
83 pounds of nitrogen, 18 pounds of phosphoric acid, and 88 pounds 
of potash. These elements are required by all field crops, and, in 
addition to these, seven other elements are required in much smaller 
quantities. These elements are always present in agricultural soils 
in larger or smaller quantities. The two questions, therefore, with 
regard to soil fertility, so far as the composition of the soil is con- 
cerned, are whether the required elements are present in sufficient 
quantity to produce the desired crop and whether the elements are 
available or soluble in such quantity and at such time during the 
growing season as the plant requires. In addition to the presence 
of these elements, as indicated above, the soil must be in proper physi- 
cal condition to promote plant growth in order to be fertile. In the 
production of sugar beets a moderately fertile soil is required. If the 
soil is lacking in fertility the roots may be too small to produce suffi- 
cient tonnage to make the crop profitable to the grower. 
Under ordinary farm conditions there is little clanger of the soil 
being too fertile for satisfactory beet growing. Occasionally spots 
are so fertile that large roots low in sugar are produced, as, for 
example, an old feed lot, a barnyard which has been turned into a 
portion of the field, or a spot where an old straw stack has been left 
to decay. These areas are small and insignificant when compared 
with the total sugar-beet acreage in the United States, but they 
sometimes have an important bearing upon the results on an indi- 
vidual farm, especially where the sugar-beet acreage on that par- 
ticular farm is small. The greatest danger from the standpoint of 
fertility arises from the lack of those physical conditions or the 
absence of available plant foods to produce large yields. The prin- 
cipal problem, therefore, in this connection lies in the improvement 
of the fertility of the soil. Soils may be rendered infertile through 
natural causes, such as leaching, and through artificial causes, such as 
single cropping, improper crop rotation, and the improper propor- 
tion of live stock to crop production. One of the principal methods 
that may be employed to' increase soil fertility is the addition of 
humus to the soil, either in the form of stable manure or of green 
crops plowed under. 
Stable manure. — One of the most satisfactory methods of supply- 
ing humus to the soil is the proper use of stable manure. A close 
relation should exist between the number of live stock on the sugar- 
beet farm and the acreage under cultivation. Studies in prac- 
tically all parts of the sugar-beet area indicate that the number of 
live stock on most farms is too small for the most profitable produc- 
tion of crops and is usually below the possibilities in both live stock 
