PAPERS ON BIOLOGY AND AGRICULTURE 239 



LEGUMES AS A SOURCE OF NITRATE FOR FARM 



CROPS 



H. J. Snider, University of Illinois 



The maintenance of an adequate supply of available 

 nitrogen is probably the most important practical soil 

 problem with which the farmer of today has to deal. 

 This problem is not limited to any particular area or to 

 any one country, for the production of agricultural pro- 

 ducts the world over is limited by an insufficient supply 

 of nitrogen. This is by no means a difficulty of recent 

 origin, because there are records showing that a shortage 

 of nitrogen caused some apprehension among the old 

 Roman farmers. 



The peculiarity of the nitrogen supply is that there 

 is a superabundance of free nitrogen in the atmosphere 

 which must be combined with other elements before 

 it may be utilized for growing crops. It is said that 

 there is in the atmosphere 5.8 tons of free nitrogen for 

 each square yard of earth surface, and it is estimated 

 that there is less than one ounce of combined nitrogen 

 per square yard of earth surface in the service of man. 

 The supply of free nitrogen is almost inexhaustible, and 

 in comparison the supply of combined nitrogen now in 

 use seems insignificant. 



Converting free atmospheric nitrogen into combined 

 nitrogen is a process which is of vital importance to all 

 classes of people. There are several practical methods 

 for manufacturing combined nitrogen, but at present 

 these processes are not sufficiently developed to furnish 

 economically any considerable amount of available nitro- 

 gen which might be used on a large scale as a soil fer- 

 tilizer. In the production of our grain crops at the 

 present time, it is necessary to look to some other source 

 for a supply of combined nitrogen. The most economical 

 and practical means of securing this nitrogen supply 

 for farm crops at present is by the utilization of the 

 various leguminous plants. 



It has long been known that leguminous plants have 

 the power of enriching the soil, but it was not until com- 

 paratively recent years that the process has been well 



