394 THE PRINCIPLES OF SOIL MANAGEMENT 



mediate and final products of decomposition assisting 

 plant production by contributing nitrogen and certain 

 mineral compounds that are a directly available source 

 of plant nutriment, and also by the effect of certain 

 of the decomposition products upon the mineral 

 substances of the soil, by which they are rendered 

 soluble and hence available to the plant. 



Through these operations the supply of carbon and 

 nitrogen required for the production of organic matter 

 is kept in circulation. The complex organic compounds 

 in the bodies of dead plants or animals, in which con- 

 dition plants cannot use them, are, under the action 

 of micro-organisms, converted by a number of stages 

 into the very simple compounds used by plants. In 

 the course of this process, a part of the nitrogen is 

 sometimes lost into the air by conversion into free 

 nitrogen, but fortunately this may be recovered and 

 even more nitrogen taken from the air by certain other 

 organisms of the soil. 



The slime molds, bacteria, fungi and algse all play 

 a part in these processes, but none of them so actively 

 during every stage of the process as do the bacteria. 

 Molds and fungi are particularly active in the early 

 stages of decomposition of both nitrogenous and non- 

 nitrogenous organic matter. Molds are also capable 

 of ammonifying proteins, and even reforming the 

 complex protein bodies from the nitrogen of ammonium 

 salts. Certain of the molds and algse are apparently 

 able to fix atmospheric nitrogen, and contribute a 

 supply of carbohydrates required for the use of the 

 nitrogen-fixing bacteria. 



