86 DRY-FARMING 
ures 22-26 further give an idea of the degree to 
which roots fill the soil. 
Depth of root penetration 
The earlier root studies did not pretend to deter- 
mine the depth to which roots actually penetrate 
the earth. In recent years, however, a number of 
carefully conducted experiments were made by the 
New York, Wisconsin, Minnesota, Kansas, Colorado, 
and especially the North Dakota stations to obtain 
accurate information concerning the depth to which 
agricultural plants penetrate soils. It is some- 
what regrettable, for the purpose of dry-farming, 
that these states, with the exception of Colorado, 
are all in the humid or sub-humid area of the United 
States. Nevertheless, the conclusions drawn from 
the work are such that they may be safely applied 
in the development of the principles of dry-farming. 
There is a general belief among farmers that the 
roots of all cultivated crops are very near the surface 
and that few reach a greater depth than one or two 
feet. The first striking result of the American inves- 
tigations was that every crop, without exception, 
penetrates the soil deeper than was thought possible 
in earlier days. For example, it was found that 
corn roots penetrated fully four feet into the ground 
and that they fully occupied all of the soil to that 
depth. 
