UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES II 3 
servation. Some species of legume find in a certain soil the tuber- 
cle organism adapted to them, while other species of legume may 
not find the proper organisms in the same soil. The soy bean isa 
most excellent crop for nitrogen gathering since it is an extremely 
luxurious growing legume, producing abundant tubercles and a 
large fixation of nitrogen when supplied with the organisms which 
produce tubercles. But in order to make use of this crop it may 
be necessary to import the proper bacteria from other soils. On 
the other hand, there are some species of legumes, like most kinds 
of peas, which are capable of growing in most soils and producing 
an abundance of tubercles. 
Further, a legume, which, during the first season produces only 
a small number of tubercles, may succeed better the second year 
than the first and may fix more nitrogen. The growth of the crop 
in the soil during the first year apparently either increases the 
number of soil organisms appropriate to this particular legume or 
produces such changes in the physiological character of the 
bacteria present that they are better adapted to the legume. In 
either case, the second season will show a more luxuriant growth 
and a more successful nitrogen fixation. 
Soil Inoculations —Experience has shown that it is not always 
possible to get a good growth of the desired legume, because of the 
failure to obtain a proper quantity of tubercles. That this is due 
to the lack of the right variety of bacteria in the soil seems certain, 
and has led to the practice of inoculating the soil. The first 
method of doing this is to obtain soil from some locality where the 
legume is known to produce a goodly number of tubercles and 
then either to mix this soil with that of the field to be planted, or 
to make a soil infusion to be used for soaking the seeds or for 
watering the young ‘plants. The results of this procedure are, in 
the main, satisfactory, for generally the production of tubercles is 
thus stimulated, and much increased crops produced (Fig. 26). 
In many instances of this kind it has been found possible to cul- 
tivate a legume in soils in- which it would not previously grow, by 
8 
