CHAPTER XXII 

 CROP ROTATION 



682. The necessity. — Crop rotation has long been 

 recognized as a necessity. Its value has been more evi- 

 dent, perhaps, in the production of cereals and the gen- 

 eral farm crops than in vegetable growing, but it is 

 scarcely less important. Numerous examples might be 

 cited of decline in yields and quality, due primarily to 

 the failure to rotate. In some instances entire communi- 

 ties have been forced practically to abandon the culture 

 of a certain crop mainly because of its continuous or too 

 frequent production. 



683. Relation to food supply. — Plants differ greatly in 

 their food requirements. Some utilize large amounts of 

 nitrogen, while others must have liberal supplies of the 

 mineral elements. Crops which have about the same 

 food requirements should not be planted consecutively, 

 if it can be avoided. When cabbage follows cabbage> or 

 lettuce follows lettuce, a heavy draft is made upon the 

 supply of nitrogen. If, instead, these crops were followed 

 by tomatoes the food supply would be utilized more 

 economically, successful crop production would be more 

 certain and the yielding power of the soir would be con- 

 served to better advantage. Many examples might be 

 given to illustrate this point. While this principle should 

 always be considered, certain conditions, as the use of 

 muck soils or the accessibility of cheap supplies of 

 manure, may justify a system of cropping which would 

 not be permissible under other circumstances. 



684. Relation to humus. — Crops differ widely in their 

 ability to supply humus to the soil, and therefore to 

 change the physical as well as the chemical properties 



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