CHAPTER XX 

 FARM MANURES CONCLUDED 



GREEN-CROP MANURES 



GREEN-CROP manures are crops grown and plowed 

 under for the purpose of improving the fertility of 

 the soil. 



The main object of turning these crops under is 

 to furnish the soil with humus. Any crop may be 

 used for this purpose. 



By growing any of the class of crops called 

 Legumes we may add to the soil not only humus but 

 also nitrogen. Cowpeas, beans, clover, vetch and 

 plants having foliage, flowers, seed pods and seeds 

 like them are called Legumes. 



Most of the farm plants take their nitrogen from 

 the soil. This nitrogen is taken in the form of 

 nitric acid and nitrogen salts dissolved in soil water. 

 The legumes, however, are able to use the free 

 nitrogen which forms four-fifths of the atmosphere. 

 This they do not of their own power but through 

 the aid of very minute plants called bacteria or 

 nitrogen-fixing germs. These germs are so small 

 that they cannot be seen without the use of a pow- 

 erful microscope. It would take ten thousand aver- 



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