86 SOIL CONDITIONS AND PLANT GROWTH 



produced being i : 8 -9. For complete oxidation of the carbon, hy- 

 drogen, and sulphur of the albumin molecule the ratio would be 

 I : 1 0*3 ; but the change was known to be incomplete, and small quan- 

 tities of leucine, tyrosine, and fatty acids could also be detected. Free 

 oxygen, however, was not essential. When grown in a culture solution 

 containing sugar and nitrate the organism took its oxygen from the 

 nitrate, but it still produced ammonia. 



Subsequent developments have been entirely on the bacteriological 

 side. A number of organisms are now known to produce ammonia 

 from complex nitrogen compounds, but soil bacteriologists have gener- 

 ally preferred to study the group as a whole, rather than isolate and 

 study individual members. The application of this method of " physio- 

 logical grouping" to soil problems is due to Remy (237). Soil is 

 inoculated into a I per cent, peptone solution, and the ammonia pro- 

 duced after four days at 20 is taken as a measure of the " putrefactive 

 power " or, as it is often called, the " ammonifying power " of the soil. 

 Remy showed that certain soils known to give good crop returns for 

 organic manures also possessed high putrefactive power, while Lohnis 

 and Parr (186) have made the interesting observation that the putre- 

 factive power of a soil falls off in winter, but rises in spring and con- 

 tinues at the higher level till late autumn. As a means of comparing 

 soils the method gives better results if curves are plotted, showing the 

 respective rates of ammonia production (Russell and Hutchinson (240)). 

 But Stevens and Withers (271) have shown that it is very limited in its 

 application, its chief use so far has been as an analytical test ; l it has 

 thrown little or no light on the processes going on in the soil. Indeed, 

 so dependent is bacterial activity on temperature, concentration, reaction 

 of medium (whether acid or alkaline), and other conditions that it may 

 be doubted whether any method of study, except in the actual soil itself, 

 will further our knowledge very much. Much better results are ob- 

 tained by studying the rate at which nitrates form in the soil, this 

 being, as we shall see later, the same as the rate of ammonia pro- 

 duction. Soil bacteria can decompose other nitrogen compounds 

 besides protein. Lohnis (187) has shown that they possess the re- 

 markable power of decomposing calcium cyanamide Ca : NC N to 

 form NH 3 and CaCO 3 , while other investigators have claimed that 

 ferrocyanides, cyanides, and cyanates are also decomposed by soil 

 bacteria. 



1 E.g. Lipman (176) has used it for testing nitrogenous organic manures. 



