CHAPTER XX. 

 HOW LEGUMES HELP THE FARMER. 



We have said a great deal about leguminous plants and their great value 

 in restoring and keeping up the fertility of the soil. We wish to make 

 perfectly plain what the work of these plants is, and what we can expect 

 from their use ; and also to correct some erroneous notions in regard to them. 

 The name legume, has been given to the family of plants to which the pea 

 belongs, because they bear their fruit in the form of a pod, called by botan- 

 ists, a legume. Hence, the name of the botanical order is leguminosae, or 

 pod bearers. 



It was noticed for many years that the members of this order of plants 

 did, in some way, add fertility to the soil in which they grew, and that 

 there was more nitrogen present than the soil possessed before the crop was 

 grown. Scientists came to the conclusion that in some way they were able 

 to get and use the free nitrogen, so plentiful in the air everywhere. Just 

 how they did this was for many years the subject of earnest investigation, 

 and is still a matter for scientific inquiry, for although we have learned a 

 great deal in regard to the agency through which they are able to get the 

 nitrogen, there is yet much to learn in regard to the exact process that goes 

 on in the soil during the growth of the leguminous crop. For all the pur- 

 poses of the farmer, however, it is sufficient to know that he can, through the 

 medium of a crop of peas or clover, get enough of organic nitrogen stored 

 in his soil to at least carry the following crop on the land, if not more ; and 

 that he can do this while growing the most valuable food crop for his stock. 



NITRIFICATION IN GENERAL. 



Nitrogen is found in all cultivated soils in three forms, of ammonia, 

 nitrates and as organic matter containing nitrogen. Very little exists in 

 the soil in the form of ammonia, as the process of nitrification rapidly 

 changes any ammonia that may be there into nitric acid. Usually the nitrogen 

 in the soil, in the form of nitrates of potash, lime or magnesium, is not over 



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