t16 RECLAIMING LOST NITROGEN 
the farmers in a still vigorous condition, and of finding some device 
by which the farmers can successfully inoculate legumes with cul- 
tures have been regarded as the primary obstacles. Moreover, 
some soils are already stocked with proper tubercle bacteria so 
that the addition of more would be superfluous. At the present 
time the pure cultures of the legume organisms that have been 
put on the market for soil inoculation are more reliable than they 
were a few years ago, but they are not always efficient. 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 
increased 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. When these crops are thus plowed into the soil they 
are brought at once within reach of the soil bacteria. 
The bacteria seize hold of the proteid products in the plants, 
as well as the cellulose and other organic substances, and cause 
their rapid decomposition. After this process is finished the 
nitrifying bacteria in the soil oxidize the ammonia left after the 
decomposition ceases and convert it into nitrate. Thus, after 
a few weeks, a considerable portion of the nitrogen material 
which was fixed in the legume has been converted into nitrate, 
available for plant life. These remain in the soil and may be 
