264 CROP ROTATION 



necessary a change in the cropping plan. Moreover, varying soil 

 conditions and the desire of the farmer to meet feeding require- 

 ments often prevent the establishment of a fixed rotation for the 

 entire farm. 



One-crop System. In contrast to crop rotation is the 

 one-crop system in which one kind of crop is grown year after year 

 on the same land. This is often called "continuous cropping." 

 There are many examples of this in the corn belt, wheat belt, cotton 

 belt, etc. 



Why Crops Are Rotated. Crop rotation has largely been the 

 outgrowth of farming experience. Its beneficial effects have long 

 been known, though the reasons were not understood. Even 

 today some of the effects of crop rotation are not clearly under- 

 stood. The primary object of rotation is to increase crop pro- 

 duction and to help maintain productive farming. This is the 

 cumulative effect of several specific benefits derived through this 

 practice, which are: (a) It helps to eliminate injury due to certain 

 insect pests; (b) it aids greatly in avoiding injury from certain 

 diseases; (c) it favors the accumulation of soil organic matter; 

 (d) tilth may be improved; (e) it favors the conservation of 

 fertilizing elements; (/) it aids in solving certain liming and 

 fertilizing problems; (</) weeds are better controlled. 



Rotation Controls Certain Insects and Plant Diseases. 

 Many truck growers, particularly, much prefer to grow certain 

 crops continuously on the same land, because when the soil is 

 fitted to meet the requirements of a special crop it is easier to 

 succeed with it. This explains the tendency to grow crops like 

 cabbage, sugar beets, onions, and in some localities, potatoes, 

 on the same land several years in succession. Though it is conven- 

 ient at times to practice a one-crop system with certain crops, 

 yet general experience teaches that it is a wiser plan to practice 

 rotation, since many records show that certain pests and plant 

 diseases finally compel the farmer to rotate. Some crops are 

 especially attacked by certain soil-dwelling insects or are pecu- 

 liarly susceptible to certain diseases which may infest the soil. 

 The continuous growing of one crop favors the development of 

 some such insect or disease until finally the crop is unable to resist 

 its attacks. The growing of other crops not affected by the 

 particular insect or disease must necessarily result in the soil 

 becoming rid of the insect or disease, because these other crops do 

 not favor its development nor its continuance in the soil. 



