24 DRY-FARMING 
pheric precipitation per year are not safe for dry- 
farm purposes. What the future will show in the 
reclamation of these deserts, without irrigation, is 
yet conjectural. 
Arid, semiarid, and sub-humid 
Before proceeding to an examination of the areas 
in the United States subject to the methods of dry- 
farming, it may be well to define somewhat more 
clearly the terms ordinarily used in the description 
of the great territory involved in the discussion. 
The states lying west of the 100th meridian are 
loosely spoken of as arid, semiarid, or sub-humid 
states. For commercial purposes no state wants to 
be classed as arid and to suffer under the handicap 
of advertised aridity. The annual rainfall of these 
states ranges from about 3 to over 30 inches. 
In order to arrive at greater definiteness, it may 
be well to assign definite rainfall values to the ordi- 
narily used descriptive terms of the region in question. 
It is proposed, therefore, that districts receiving 
less than 10 inches of atmospheric precipitation 
annually, be designated arid ; those receiving between 
10 and 20 inches, semiarid; those receiving between 
20 and 30 inches, sub-humid, and those receiving over 
30 inches, humid. It is admitted that even such a 
classification is arbitrary, since aridity does not alone 
depend upon the rainfall, and even under such a 
