LEGUMES AND SOIL FERTILITY 



173 



potassium in each soil is sufficient for over 1,000 years. Of 

 course, a crop would never remove all the nitrogen or phosphorus 

 from a soil, but in actual practice the elements are slowly re- 

 moved and the crop yields reduced each year until a certain mini- 

 mum is reached. When crops can no longer be produced economi- 

 cally then the owner abandons his soil, moves on to virgin soils, 

 or if it be in an old district he resorts to the expensive commercial 

 fertilizer. However, the illustration is sufficiently accurate to 

 clearly indicate that nitrogen is the limiting factor in so far as 

 soil fertility is concerned in both of these soils. This is true of 

 the great majority of soils; therefore, an increased nitrogen sup- 

 ply in them means an increased yield. This principle is one of 

 the fundamentals of soil fertility. 





Nitrogen 



Phosphorus 



Potassium 



Greenville Farm (Logan^ Utah) 









Pounds per acre 



4,904 



2,700 



60,560 



Total removed in a 50 bushel 









wheat crop 



96 



16 



58 



No. of 50-bushel crops wheat 



51 



169 



1,045 



Total removed in 20 tons 









sugar beets 



100 



18 



157 



No. 20 ton crops beets 



49 



150 



380 



NepM Farm {NepM^ Utah) 









Pounds per acre 



3»744 



8,388 



87,840 



No. 50-bushel crops wheat 



39 



524 



hSH 



Nitrogen. — Nitrogen exists in the atmosphere in inexhaustible 

 quantities. Every square yard of land has seven tons of nitrogen 

 lying over it, or if the quantity covering one acre could be made 

 into nitrates it would be worth as a fertilizer $125,000,000. 

 Now we have sttn that the legumes — ^peas, beans, alfalfa, clover, 

 and vetches — when properly inoculated have the power of feed- 

 ing on this vast ocean of atmospheric nitrogen, whereas the non- 

 legumes — barley, wheat, oats, etc. — must depend upon the supply 

 within the soil. The farmer must take advantage of this fact 



