190 DRY-FARMING. 
moisture of two seasons for the use of one crop; and 
to set free fertility to enable the plant to grow with 
the least amount of water. It is not yet fully under- 
stood what changes occur in fallowing to give the soil 
the fertility which reduces the water needs of the 
Fic. 46. Dry-farm potatoes, Rosebud Co., Montana, 1909. Yield, 282 
bushels per acre. 
plant. The researches of Atkinson in Montana, 
Stewart and Graves in Utah, and Jensen in South 
Dakota make it seem probable that the formation of 
nitrates plays an important part in the whole process. 
If a soil is of such a nature that neither careful 
deep plowing at the right time nor constant crust 
