25 
(6) When the amounts of casein were varied, other conditions 
remaining constant, the yields of ammonia in four days increased 
as the amounts of casein present increased; 48.4 per cent of the total 
nitrogen in 0.2 gram was ammonified, 57 per cent in 1 gram, 60.9 
per cent in 2 grams, and 65.9 per cent in 3 grams. It seems probable 
that decreasing percentages of the total nitrogen were assimilated 
by the organisms present as the amounts present increased, but there 
are probably other factors of a chemical and biological nature 
involved. 
(7) The yield of ammonia from casein was not materially increased 
by extending the incubation period beyond four days, and the 
decomposition of the second and third gram, added after one gram 
had been acted upon four and eight days, respectively, was slightly 
more vigorous than that of the first gram. In each instance approxi- 
mately 60 per cent of the total nitrogen was found as ammonia. 
These facts, taken in connection with the above, indicate that the 
incomplete ammonification was not due to the inhibitory effect of 
the decomposition products, but rather that a part of the nitrogen 
of casein is extremely resistant to ammonification. It is also possi- 
ble that a large part of the remaining nitrogen was assimilated by 
the bacteria. 
(8) Casein when mixed with silica sand or in solution was com- 
pletely hydrolyzed by the action of bacteria in seven days. In the 
former instance, 64.2 per cent of the nitrogen was ammonified and in 
the latter 59.53 per cent. In solution the rate of hydrolysis exceeded 
that of ammonification, but the latter was not so active during the 
first five days as when mixed with soil (see Series IV). 
(9) The determination of the different groups of nitrogen com- 
pounds before and after bacterial action in casein, dried blood, soy 
bean cake meal, cottonseed meal, linseed meal, coconut meal, globulin 
from cottonseed meal and zein from maize shows that, with the 
exception of linseed meal and zein, the basic diamino acid nitrogen 
was converted into ammonia more rapidly than the nitrogen of other 
groups. With casein, soy bean cake meal, and cottonseed meal the 
more rapid ammonification of the basic nitrogen was especially 
noticeable. When this fact and the above are considered in connec- 
tion with a comparison of the organic nitrogen of soils and vegetable 
proteins, it becomes apparent that all portions of the organic nitrogen 
in the different materials used as fertilizers and green manures are not 
equally susceptible to ammonification. It is evident, therefore, that 
chemical factors inherent in the nitrogen compounds themselves 
predetermine the availability to some degree. Further investigation, 
including a study of the decomposition of individual amino acids 
and acid amids, is being made. 
