CHAPTER XVI 

 ROTATION IN DRY AREAS 



Rotation means an interchange in the succession 

 of the crops grown with a view to the better main- 

 tenance and improvement of the soil with reference to 

 chemical and physical conditions. 



The nature of the interchange will depend more or 

 less on the kinds of the crops that it is desired to grow, 

 and on the adaptation of the natural conditions for 

 growing them. Any interchange in the succession con- 

 stitutes rotation in a sense, but such interchange does 

 not of necessity result in either the maintenance or im- 

 provement of the conditions that govern production. 

 Rotation in non-leguminous cereals only may tend to 

 some extent to lessen weed production, but it does not 

 in any way increase the plant food in the land. When 

 cultivated crops are grown in interchange with this 

 class of cereals, the cleaning of the land is much facilitat- 

 ed, but the depletion of the plant food goes on unless 

 one or more of the crops grown is a legume. Increase 

 in production is best secured in the absence of the use 

 of commercial fertilizers when the rotation is of a char- 

 acter that will improve the tilth of the soil and its 

 moisture-holding power, and will also increase the in- 

 crement of plant food in it. To secure all of these bene- 

 fits calls for the introduction of a grass or clover crop 

 into the rotation, preferably the latter, which in itself 

 meets all the requisites sought as stated above. 



Positive reasons for rotations in humid areas. It is 

 necessary in these for the following reasons, among 

 others, that may be given: To maintain an equilibrium, 

 (1) in plant food; (2) in the humus supply; (3) in the 

 mechanical condition of the soil, and (4) in the food 

 products grown. 



