THE DECOMPOSITION OF CELLULOSE IN SOILS 479 



Phosphoric acid is so tenaciously held by most soils that ordinary 

 leaching of the soil due to natural rainfall or irrigation would seem to 

 bring very small amounts of this valuable substance into solution. The 

 action of carbon dioxide upon the insoluble phosphorus compounds of the 

 soil may proceed as foUovv^s : 



Ca,(POJ, + 2CO2 + 2H3O = Ca^H^CPOJ^ + Ca(HC03)p 



A large portion of the CO, resulting from the decomposition of 

 cellulose or other carbonaceous materials in soils is ultimately returned 

 to the atmosphere where it may be used over and over again in the manu- 

 facture of sugar, starches, cellulose, etc. in new generations of plants. If 

 it were not for the activity of cellulose-dissolving organisms in the soil 

 developing in association with gas producing organisms, the cycle of 

 change to which carbon is subject would soon come to a standstill and the 

 carbon supply of plants soon be depleted. 



The importance of cellulose destruction in soil may then be summar- 

 ized as follows : 



1. The decomposition of cellulose under proper soil conditions and 

 in association with the nitrogenous compounds of plant tissues makes 

 possible the maintenance of the soil humus which is so essential in main- 

 taining the proper tilling qualities of the land. 



2. The cellulose added to the soil represents a large amount of poten- 

 tial energy which must have a marked stimulating effect on nitrogen 

 fixation and many other important biological processes going on in the 

 soil. 



3. The decomposition of cellulose in soils, under proper conditions, 

 results in the formation of large quantities of carbon dioxide. The action 

 of carbonic acid in rendering available various mineral constituents of the 

 soil is recognized as an important factor in the maintenance of soil fer- 

 tility. 



4. Through the decomposition processes, the carbon locked up in the 

 cellulose is ultimately returned to the atmosphere, thus maintaining the 

 carbon cycle and rendering the carbon supply for plants inexhaustible. 



Summary 



1. The cellulose agar plate method is the most satisfactory for iso- 

 lating pure strains of bacteria, filamentous fungi or Actinomyces which 

 have the power of dissolving cellulose. 



2. In the preparation of precipitated cellulose for cellulose agar, the 

 copper-ammonium-cellulose solution as well as the acid used should be 

 very dilute. If either of the solutions are too concentrated, the precipi- 

 tate is likely to be coarse, which not only makes it difficult to wash, but 

 unsatisfactory for the preparation of culture media. A uniformly fine 

 cellulose precipitate can be secured by diluting one part of the copper- 

 ammonium-cellulose solution with forty parts of water and mixing with 



