1922] GREAVES—SOIL 173 
and furthermore, it is usually those salts which are considered 
soil amendments that exert the greatest influence. What effect 
would these salts have on the total nitrogen of the soil? This is 
answered in table IX. 
Again potassium is least efficient, while sodium is one of the 
most efficient. It is interesting to note that the nitrates, which 
are usually stated as retarding azofication, stimulate it to a greater 
degree than any of the other compounds. In this respect calcium 
nitrate is more efficient than any other salt. This probably 
indicates that it is best to add nitrates to the soil in this form. 
It could not be claimed that this compound was carrying available 
calcium to the soil, for this soil already contains some 40 per cent 
of calcium and magnesium carbonate. 
It is evident that these salts would increase both total and 
available nitrogen in the soil. They would also increase the 
crop-producing power in another way, namely, by increasing both 
directly and indirectly the available potassium and phosphorous of 
the soil (10). 
SOLVENT ACTION OF BACTERIA. Betws (3) found that twelve 
out of twenty-three bacteria isolated from soil exerted a definite 
solvent action on difficultly soluble plant food. One organism 
which produced no gas, but a large amount of acid, exerted the 
greatest solvent action upon calcium carbonate; while other organ- 
isms which produced gas (largely carbon dioxide), but not as much 
acid as the former, gave an action more marked than of the stronger 
acid producer upon the dicalcium and tricalcium phosphates. 
Bacillus subtilis, B. mycoides, B. proteus vulgaris, and B. coli com- 
munis, as well as several agar cultures from garden soil, were 
found (26) to be capable of dissolving the phosphates of bone and 
to a less extent those of mineral phosphates. The greatest solvent 
action was exerted in media containing sodium chloride, potassium 
sulphate, and ferrous sulphate. Even yeast (17) may play an 
important part in dissolving phosphates. KRoBER, however, 
considers that the life activity of the bacteria, that is, assimilation 
of phosphorus by the living organism, plays little or no direct part 
in solution of the phosphates, but that the latter is due to the 
action of the organic acid and of the carbon dioxide produced. 
