392 THE KM ALL GRAINS 



wheat after wheat yielded 15.66 bushels an acre compared 

 with 28 bushels for wheat after fallow. Even in this in- 

 stance, the latter method was more profitable because of the 

 greater cost of the 2 crops in the former, but no doubt 

 the difference in favor of summer tillage would ordinarily 

 be greater, as even the wheat after wheat, in this experi- 

 ment, was only the second crop from a summer fallow. 

 However, a rotation including a green-manure crop and, 

 if possible, an intertilled crop, is the method most needed. 



417. Summer tillage in the Columbia Basin. In 

 this district, summer tillage is an established practice of 

 long standing. The soil is of such a texture that more 

 water is retained in it than in the soils of othef districts. 

 It is probably necessary to summer-till every second 

 year when the rainfall is 16 inches or less. With a rain- 

 fall of 16 to 20 inches, a fallow every third year may be 

 sufficient. Where the rainfall is 20 inches or more, as in 

 the Palouse country, summer tillage seems unnecessary. 

 If summer tillage, under such a condition, increases the 

 yield, it is likely to be due to an increase in the available 

 plant-food, rather than available moisture. Even with 

 a rainfall of 12 inches and over, it may be possible to sub- 

 stitute profitably an intertilled crop in place of the summer 

 tillage alone. 



418. Soil-blowing. Almost throughout the Western 

 area, the soils are in many places subject to blowing and 

 drifting. The tendency is specially strong in the volcanic 

 soils of the Columbia Basin and eastern Oregon and, 

 where not irrigated, in those of the Imperial Valley. As 

 in those parts of the Great Plains where soil-blowing 

 occurs, so also in this area, there is always a lack of 

 humus associated with this condition. It is said that soil- 

 blowing, except in very dry and sandy sections, is due 



