SOME GENERAL PRINCIPLES SI 



peas and velvet beans, have even greater power to 

 gather nitrogen from the air and store it in the soil 

 than clover, since the nodules formed on the roots of 

 these are frequently larger. In some instances, on 

 the roots of the velvet bean they grow in clusters as 

 large as an ordinary potato. VVith reference to all 

 these leguminous plants it has been demonstrated 

 that under proper conditions good crops may be 

 grown and removed from the soil and leave it much 

 richer in nitrogen than when the seed was sown. 

 It is thus possible by sowing these crops at suitable 

 intervals to keep the soil sufficiently supplied with 

 nitrogen to grow good crops other than legumes, 

 adapted to the locality, without the necessity for 

 purchasing the nitrogen of commerce in any of 

 its forms. They may be made to more than main- 

 tain the supply of nitrogen, notwithstanding the 

 constant loss of the same by leeching down into the 

 subsoil in the form of nitrates, and through the more 

 or less constant escape of the same into the air in the 

 form of ammonia, during those portions of the year 

 when the ground is not frozen. 



They will do this in addition to the food supplies 

 which they furnish, hence they may be made to sup- 

 ply this most important element of fertility, and by 

 far the most costly when purchased in the market, 

 virtually without cost. The favorable influences 

 which these plants thus exert upon crop production 

 is invaluable to the farmer. They make it possible 

 for him to be almost entirely independent of the 

 nitrogen of commerce, which, at the rate of con- 

 sumption during recent years, will soon be so far 



