ROTATION IN DRY AREAS 393 



not be alternated with the summer-fallow, since the 

 moisture that has been stored by the fallowing process 

 is more needed by the cereal crops that are grown in the 

 rotation. A crop of any of the cereals is not assured in 

 the absence of stored moisture, whereas a cultivated crop, 

 as corn, is much more certain under such conditions. 



The benefits from such a rotation include the fol- 

 lowing: (1) It makes it possible to grow good yielding 

 grain crops in areas where the moisture is so low that 

 these could not be obtained in any other way; (2) it 

 makes it easily possible to maintain cleanliness in the 

 land; (3) it makes it possible to furnish supplemental 

 forage where it could not otherwise be obtained. In 

 some areas the precipitation is so light that grain crops 

 could not be grown by any other system of farming that 

 could be followed. The choice in these is between no 

 grain crop and the summer-fallow. Where this rotation 

 is practised land may be kept absolutely clean. True, 

 grain may volunteer, but the summer-fallow makes it 

 possible to destroy it (see p. 119). In some areas where 

 the seasons are very short, so short that grain may not 

 be depended on to ripen, it may be devoted to forage 

 uses. 



This rotation may be necessary in many portions 

 of the dry belt. If grain is to be grown it may be neces- 

 sary where the rainfall is too little to grow a crop of 

 grain after "a cultivated crop. The difference in the de- 

 gree of the precipitation that will make grain succeed 

 on fallow land and. fail when sown after cultivated land 

 has not been well worked out, but such a difference does 

 doubtless exist. As expressed in inches, however, the 

 difference may not be very great. Where the precipita- 

 tion is less than, say, 8 inches on the average, the sum- 

 mer-fallow would seem to be a necessity where crops of 

 any kind of grain are to be grown. This rotation is 

 practised where the rainfall is considerably greater than 



