THE BIOCHEMICAL DECOMPOSITION OF NITROG- 
ENOUS SUBSTANCES IN SOILS. 
INTRODUCTION. 
The chemical changes produced in the nitrogenous substances of 
soils by bacteria are of great importance. As is well known, the end 
products are ammonia, nitrate, and free nitrogen, but the interme- 
diate steps of the change, which are probably of great importance, 
are only imperfectly understood. It appears that proteins undergo 
progressive decomposition in soils similar to that which takes place 
in animal digestion, and it is highly probable that ammonification 
is preceded by hydrolysis. From the investigations of Schreiner et 
al. 1 it has been shown that small amounts of protein and nucleo- 
protein cleavage products are widely distributed in soils ; and Lohnis 
and Green 2 recently found from ammonification experiments with 
flesh meal that in the early stages of the action greater amounts of 
ammonia were obtained by distilling a 1 per cent hydrochloric acid 
extract with caustic soda than with magnesia. They held that the 
caustic soda decomposed soluble hydrolytic products (amino acids) 
split off by the bacteria. At a later stage, when the amino acids had 
presumably been more completely decomposed, the yields of ammonia 
by the two methods were more nearly equal. 
It is probable that not all of the nitrogen in a given protein is 
equally susceptible to ammonification s and that different proteins 
undergo decomposition at different rates, even when all other con- 
ditions are equal. In ammonification experiments, for example, it 
is seldom that more than from 50 to 60 per cent of the nitrogen 
added is recovered as ammonia, and different nitrogenous substances 
yield ammonia at greatly different rates. As is well known, the main 
portion of the nitrogen in soils occurs in organic forms and has pre- 
viously existed as vegetable protein. After the organic matter of 
soils has been acted upon by bacteria for a time a residue, rich in 
nitrogen, and commonly called humus, is left, which undergoes further 
decomposition at a very slow rate. Moreover, the rate of formation 
of ammonia from humus appears to depend to some extent on the 
conditions under which the humus was itself formed. Generally acid 
" U. S. Dept. Agr., Bur. Soils Bdls. 53, 74, 80, 83, 88. 
iCentbl. Bakt. [etc.], 2. AM., 37 (1913), pp. 534-562. 
»See Jodidi, Iowa Sta. Research Bui. 9 (1912). 
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