SOIL SANITATION 287 



rest fallow when it begins to show signs of 

 breaking down under single-cropping. In the 

 Great Plains area extensive farming has called 

 for the manufacture of machines that "head" 

 the grain, leaving the stalks standing, to be 

 plowed under by the gang plows which fre- 

 quently are drawn by the same motive power 

 that cuts the heads and threshes the grain. This 

 is done merely because it is convenient, because 

 it is the most economical means of farming in 

 that region; the fact that returning the dry 

 stalk to the land is beneficial is merely inci- 

 dental. The straw is a drug on the market" 

 and plowing it under is the easiest means of 

 getting rid of it. It is said that four mules are 

 required for the same plowing that required 

 only two twenty years ago in some parts of 

 the irrigated districts in the West. This means 

 that the soil has become less friable, has lost 

 its optimum content of mold, is no longer 

 "loam," because of a system of farming which 

 concerns itself more with the mineral fertility 

 than the organic content of soils. 



The organic content of soils amounts usually 

 to about three per cent, of the entire bulk. 

 It is not assumed that the only or even the 

 principal use of this mold is that of ridding 



