CEREALS UNDER IRRIGATION 423 



satisfactory, compared with the flood and check methods, 

 in results secured. The first cost was higher, but labor of 

 irrigation less than with either of the other methods. It 

 was also found that furrows should not be less than 16 

 inches apart. 



451. Succession of crops. The irrigated grain crop 

 often follows the clearing of sagebrush, as it is the cheap- 

 est first crop on new land. In other cases it usually comes 

 after alfalfa or some cultivated crop such as corn, potatoes, 

 or sugar-beets. In Colorado, it is found that a good rota- 

 tion is alfalfa 3 years, potatoes or beets 3 years, wheat or 

 barley 2 years, then alfalfa again. In Utah, grain often 

 succeeds alfalfa. 



452. Preparation of the soil for seeding may follow 

 the order of plowing, harrowing, irrigating, then disking, 

 and later the use of the float. If the method of irrigation 

 is by flooding, leveling will precede that operation, unless 

 done previously. For spring seeding after fall plowing, 

 the disk harrow should take the place of the plow in the 

 spring. Often irrigation is not needed to start the crop, 

 in which case the land is plowed or double-disked (if 

 previously plowed), harrowed, floated, and seeded, and 

 then irrigated afterward. This course is particularly 

 advisable on heavy soils, which dry out very slowly, thus 

 delaying the seeding if not done before irrigating. 



453. When to irrigate. The frequency of irrigation 

 is determined largely by the character of the soil and sub- 

 soil. A heavy soil with tight subsoil may be irrigated 

 heavily but at long intervals, as it will absorb a large 

 quantity of water and hold it a long time. On the other 

 hand, light soils, especially if they have also open subsoils, 

 should be irrigated lightly but frequently. The ideal 

 condition is to give the soil sufficient moisture to germi- 



