PLOWS FOR DRY-FARMING 309 
the subsoil plow is simply a vertical piece of cutting 
iron, down to a depth of ten to eighteen inches, at the 
bottom of which is fastened a triangular piece of iron 
like a shovel, which, when pulled through the ground, 
tends to loosen the soil to the full depth of the plow. 
Fic. 78. Subsoil plow. 
The subsoil plow does not turn the soil; it simply 
loosens the soil so that the air and plant roots can 
penetrate to greater depths. (See Fig. 78.) 
In the choice of plows and their proper use the dry- 
farmer must be guided wholly by the conditions under 
which he is working. It-is impossible at the present 
time to lay down definite laws stating what plows are 
best for certain soils. The soils of the arid region are 
not well enough known, nor has the relationship 
between the plow and the soil been sufficiently well 
established. As above remarked, here is one of the 
great fields for investigation for both scientific and 
practical men for years to come. 
