DRAINAGE, IRRIGATION, AND DRY FARMING 131 



summer-fallow only once in from three to five or six years if a 

 suitable rotation of crops is carried out. Summer fallow has 

 proved more profitable for winter wheat than for the spring 

 grains or for corn or sorghum. 



158. Crops adapted to dry farming. Three important factors 

 must be considered in selecting plants to grow under dry-land 

 conditions : first, the plant should have the ability to feed upon 

 moisture stored in the lower subsoil ; second, it should make its 

 greatest growth during the season of greatest rainfall ; and third, 

 it should be able to use water economically. Wheat is the most 

 successful dry-land crop. It makes its greatest growth during 

 the spring and the early summer, when the largest part of the 

 precipitation falls, and it has the ability to obtain water from 

 deeper in the subsoil than most other farm crops. The Turkey 

 wheats are best adapted to dry-land conditions. These wheats 

 originated in Europe, and have been grown for centuries in 

 areas of light rainfall. The sorghum crops are also suited to 

 dry farming. These crops were developed under semiarid con- 

 ditions, and while they make their greatest growth during the 

 hotter and drier portion of the growing season, they have great 

 ability to withstand drought and they use water very economi- 

 cally. Oats, barley, and spring wheat are grown successfully in 

 the northern part of the dry-land area. Potatoes also give good 

 results, especially when planted upon summer-fallowed ground. 



QUESTIONS AND PROBLEMS 



1. At what depth are the tile drains of your locality usually placed? 



2. If you have an opportunity, observe the results on crops of drained 

 and undrained soil. 



3. If one of the farmers of your vicinity has placed his tile drains four 

 feet deep and another three feet deep, compare the results on their crops. 



4. If your school is located in a region which farms by irrigation, 

 secure statistics regarding the number of applications of water, the amount 

 of water used, its cost, and the products of these farms, in comparison with 

 the products of those in nonirrigated districts. 



. 5. Where and how long has dry farming been practiced? 



