108 RECLAIMING LOST NITROGEN. 
improved that they will be practical. The plan is logically a proper 
one, and if it be found possible to develop the tubercle bacteria in 
sufficient quantity and to distribute them in a living condition, 
these soil inoculations may become of great value to the agricultural 
industry. 
The reasons for failure thus far are varied. The difficulties of 
keeping the cultures pure, of distributing them to the farmers in 
a still vigorous condition, and of finding some device by which the 
farmers can successfully inoculate legumes with cultures have 
been regarded as the primary obstacles. Moreover, some soils 
are already stocked with proper tubercle bacteria so that the addi- 
tion of more would be superfluous. If, however, the claims of 
DeRossi are correct and the tubercles are caused not by the 
B. radicicola, but by another much more slowly growing organism, 
the irregularities in these results are readily explained, and it will 
be necessary to proceed along a different line in developing cultures 
of the organism that really produces the tubercles. At the present 
time, therefore, the pure cultures of the tubercle organisms that 
have been put on the market for soil inoculation are not reliable, 
although we may confidently expect that the methods will be so 
improved in the future as to make them of practical value. Mean- 
time, soil inoculations continue to be made with legume earth 
from lands where the desired legumes are growing vigorously; and 
this method of soil inoculation has proved of much practical value 
in developing a vigorous growth of legumes and a consequent in- 
creased fixation of atmospheric nitrogen. 
3. Utilization of the Nitrogen. The next problem is how 
such a store of nitrogen, fixed in the soil, may best be utilized for 
the benefit of the next crop. There are two methods by which 
this nitrogen may be made available for crops subsequently 
growing in the same soil. The first, which is commonly called 
green manuring, consists in allowing the legume to grow vigor- 
ously for a time, and then in plowing the whole crop into the soil, with 
the expectation that the nitrogen stored up in the plants will be 
available in the soil for the next crop. The method by which the 
nitrogen becomes available is based upon the facts already noticed. 
