THE BEET-SUGAR INDUSTRY IN 1920. 31 
to advantage if there is an abundance of live stock to utilize them. 
Even if certain crops could be sold from the farm at a reasonable 
return above the cost of production, it would be poor policy to sell 
them, for the reason that by so doing a large amount of plant food 
would be shipped away. Live stock, if properly handled, enable the 
farmer to keep a larger proportion of the plant foods on the farm 
than could be done if the crops themselves were removed. Feeding 
the crops on the farm is the best practice and will generally yield the 
largest returns per unit of land and per unit of labor, especially if 
the proper relations between crops, live stock, land area, and labor 
are established. It is apparent, therefore, that several objects may 
be accomplished by proper crop rotation, all of which must be kept 
in mind in order to reap the greatest returns from the sugar-beet 
farm. 
Effect on the soil. — As has been previously noted, all plants require 
certain plant foods, and these elements are utilized by different plants 
in different proportions. The rotation of crops insures a better 
utilization of these plant foods than can be obtained by growing 
a single crop. Certain crops are deep rooted, while others are more 
shallow. The deep-rooted crops tend to stir the soil to a greater 
depth and in this way make the plant foods more readily available 
for the shallow- feeding crops. Certain crops aid in the production 
of certain plant foods, as, for example, the leguminous crops store 
nitrogen, which is rendered available to the other crops grown in 
rotation with the legumes. Again, certain crops require more or 
less cultivation, as is the case with sugar beets. This stirring of the 
soil tends to expose the plant foods to the action of the elements, 
thereby rendering the mineral material available for the use of the 
beet plants and the plants of succeeding crops. 
Relation of pests to crop rotation. — The rotation of crops tends 
to reduce or to destroy those pests which depend upon certain plants 
for their existence. As is well known, some plant pests live and 
thrive only on certain plants. If these plants are grown year after 
year in the same field, they furnish favorable breeding conditions 
for the propagation and increase of these pests. By changing to 
other crops, plants upon which the pests can not live or upon which 
they do not thrive may be grown and the pests thereby destroyed or 
reduced to a minimum. Frequently the pests have resistant forms 
or stages in which they can exist in a dormant condition for seA^eral 
years, as is notably true of the brown-cyst stage of the sugar-beet 
nematode and the resting-spore stage of certain fungi. In such 
cases it is necessary to plan the rotations with a view to starving out 
these pests. To do this the rotations must be of such a length that 
crops upon which these pests can not thrive may be grown for several 
years in succession. In some cases other methods must be resorted 
