104 RECLAIMING LOST NITROGEN. 



a second species will not flourish upon it because of lack of tubercle 

 bacteria properly adapted to the second species. 



THE UTILIZATION OF THE NITROGEN-FIXING 

 POWERS OF LEGUMES. 



Although there are still unsettled questions concerning the 

 nature of the tubercles, the power possessed by legumes of fixing 

 nitrogen through their aid is of the utmost importance. The 

 legumes are the most practical means within reach for restoring to 

 the soil the nitrogen dissipated into the air, and it becomes a 

 matter of great significance to agriculture to determine the best 

 practical method of making use of this power. It would seem that 

 we have here the factor needed for making possible a cultivation of 

 the soil without exhausting its nitrogen. Virgin soil has all its 

 factors of nitrogen loss and gain nearly balanced; cultivated soils 

 have a balance on the debit side. If we can discover a practical 

 method of applying these factors of nitrogen assimilation, one of the 

 great agricultural problems will be solved. Up to the present time 

 the matter has not been brought to a condition where we can feel 

 that we know how to handle these nitrogen-fixing forces to the 

 greatest advantage; but so much has been learned that already 

 our agriculturists are making use of the knowledge to a great extent, 

 and we may fairly expect that the next few years will see these 

 forces more thoroughly under the control of the farmer than to-day. 



In making use of this means of gaining nitrogen the following 

 facts must be considered. 



i. Selection of a Proper Legume. The question of the proper 

 legume to grow in any soil, for the purpose of fixing its soil nitrogen, 

 is one that must be determined largely by experiment. In all cases 

 it should be the legume that grows most luxuriantly upon soils not 

 particularly well fertilized, and which, at the same time, produces 

 the most abundant crop of tubercles upon its roots. These factors 

 will depend upon climate, the chemical nature of the soil and the 

 variety of soil bacteria. In selecting the legume the individual 

 must take into consideration all the facts within his reach. Some 



