LEGUMINOUS ROOT TUBERCLES 2IQ 



In the third place, the nitrogen is lost to the soil by a chemical union 

 with other soil substances, so as to form insoluble compounds which are, 

 therefore, unavailable to the growing crops. The loss may also be ac- 

 complished by denitrifkation, which is due to the presence in the soil of 

 nitrate-reducing bacteria, which are active, when the soil is wet with 

 standing water and the oxygen supply is poor. Perhaps, the largest 

 amount of nitrogen is removed from the soil in the harvesting and sale of 

 the crops. These harvested crops are carried to our large centers of 

 population, or sent overseas where they are lost, as far, as returning man- 

 urial equivalents to the soil of the country in which they were produced, is 

 concerned. Crooks estimates that England alone wastes in the sewage 

 and drainage of her cities, nitrogen to the value of $80,000,000 per year. 

 Hence in the husbanding of our natural resources, the sewage from oui 

 large cities should be saved. It is so saved in China and Japan, but the 

 sewage farms, which have been tried, American and European, have not 

 been profitable, hence, the whole matter of sewage disposal by sediment 

 alone and by the septic tank is still open for exhaustive scientific research. 

 Connected with this disposal of sewage, horse and cattle manures is the 

 management of home and local markets, where the produce of our 

 farms might be utilized and the waste products, where suitable, might 

 be returned to the soil. 



Having briefly outlined the ways in which the soil becomes impover 

 ished, it is important clearly to state how the nitrogen of the soil may be 

 accumulated. One of the most important sources of supply is barnyard 

 manure, which contains large quantities of ammonia, but that ammonia 

 cannot be absorbed directly by the root hairs of the agricultural plants. 

 We have abundant experimental proof that green plants, except the 

 Leguminosae, can utilize the nitrogen only in the form of nitrates, or only 

 to a very slight extent in the form of ammoniates. We have noticed 

 how this process of nitrification takes place in two steps by the activity 

 of nitrifying bacteria, whose growth in the soil is stimulated by aeration, 

 by the requisite moisture and a feeble alkaline condition of the soil. Once 

 the ammonia is converted into nitrates, the supplies of nitrogen in the 

 soil become available to green plants. Many plants are independent of 

 this supply of nitrogen in the form of nitrates, viz., the Leguminosae, and 

 perhaps some few members of the families Betulaceae, Eleagnaceae and 

 Podocarpaceae, which can utilize free atmospheric nitrogen. 



