376 DRY FARMING 



nitrogen to produce from 2,000 to 10,000 bushels of wheat, 

 enough phosphorus to produce 5,000 to 15,000 bushels and 

 enough potassium to produce from 70,000 to 225,000 

 bushels in the surface 6 2-3 inches of one acre. 



Man would take out all this wheat in a year if he could, 

 and leave none for future generations, but Providence 

 has wisely provided that only about 2 per cent, of the 

 content of certain elements, 1 per cent, of others and 1-4 

 of 1 per cent, of still others can be annually released from 

 the soil acd taken up by growing plants, so that we can- 

 not literally deplete our soils of their potential wealth 

 by cropping even if we would; but we can and are de- 

 pleting even the best of our soils of their surplus wealth 

 and their productiveness. We must not let the sup- 

 ply of total plant food get so low that the small per- 

 centage that becomes available to plants annually will 

 be insufficient for a large crop. 



It may be asked, why add manure or other fertilizer to 

 soil containing so much plant food ? The answer is to be 

 found in the proportion of the plant food in the soil that 

 is available to plants. The elements added in decayed 

 manure are quickly available to the plant, while much of 

 that found in the soil is not. And in addition, decaying 

 organic manures not only improve the physical condition 

 of the soil, lessen its tendency, to 'blow, and improve its 

 moisture holding power, but also liberate or make avail- 

 able other more or less insoluble plant food elements. 

 Of course it costs money to handle manure and there are 

 some minor objections to its use under certain conditions. 

 "Nevertheless at many different places in the West it has 

 increased the yield of every crop tested, even on rich 

 land. 



If a system of permanent agriculture is to 'be estab- 



