Manuring and Rotations 87 
soil is used; an alternation of deep- and shallow-rooted 
crops overcomes this difficulty. 
The improvement of the soil furnishes one of the chief 
reasons for crop rotation. This improvement is made 
possible by the use of legume crops, which fix nitrogen 
from the air. The nitrogen fixed by these crops can be 
used by others which follow in the rotation, but it would 
be lost practically if legumes were raised continuously. 
The control of plant diseases, insect pests, and weeds is 
made possible by the rotation of crops; indeed, such 
considerations often compel a farmer to change his crops 
when he would not otherwise do so. Economy in the use 
of man-labor, horse-labor, machinery, and irrigation 
water results from the raising of a number of crops on 
the farm. These considerations alone, without any other 
benefits, would be sufficient for practicing rotations. 
Sugar-beets require a great deal of tillage. The land 
must be plowed thoroughly and deeply; cultivation dur- 
ing the growth of the crop is practiced; and finally at 
harvest time, the land must be stirred to considerable 
depth to get out the beets. The large roots go deeply 
into the soil and promote thorough aération, and when 
the beets are topped a large quantity of organic matter 
is added to the land from crowns and tops. All these 
practices promote a desirable condition in the soil. It is 
also highly desirable to have part of the results of these 
intensive methods of cultivation reflected in later crops. 
This end is achieved by rotating the crops. The crop 
that follows beets in the rotation is benefited by the tillage 
given to the beet crop, even though beets add no plant- 
food to the soil as do legumes, 
