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 m 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 aeration, 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. 



