238 CAMPBELL'S SOIL CULTURE MANUAL 



firm soil becomes in the least dry there is immediately a 

 process of depositing of salts and other matter between these 

 particles of soil closing the pores and consequently dimin- 

 ishing the quantity of air that should freely pass through 

 this soil to the roots. This condition not only points to 

 the fact that you are allowing the air to be shut out but that 

 you are losing moisture by evaporation from the soil which 

 may be checked by cultivation. In fact, there should be 

 no dry soil above your moisture except what is loose and 

 fine. 



Sub-irrigation is being practiced with marvelous re- 

 sults in some instances. This demonstrates clearly that if 

 the irrigator will watch his opportunity and will turn on 

 his surplus water in the fall after his crop has been removed 

 or during the winter or early spring, with the water stored 

 in the soil below and care in conserving the moisture by 

 proper cultivation, fine crops can be grown with very little 

 after irrigation. 



Very large crops of winter wheat should be grown on 

 the average soils in Colorado and sections under similar 

 conditions if special effort was carefully put forth to irri- 

 gate thoroughly, immediately after the crop is harvested, 

 then double disk as soon as the surface is sufficiently dry 

 to do the work without sticking. Plowing later using great 

 care to pack the plowed portions and harrow the surface 

 while moist, seeding sufficiently early for a good fall growth, 

 then harrow early in the spring, then with one irrigation 

 after the foliage fully covers the surface, sixty bushels per 

 acre should be common under such conditions. In all crop- 

 growing under irrigation, much consideration should be 

 given to the chapters under the following headings: "Phys- 

 ical conditon of the soil/' "air and its importance in the 

 soil" and the "water holding capacity of the soil/' 



