MICROBIOLOGICAL ANALYSIS OF SOIL 727 



be active, while in the case of a sandy soil with a total of 0.015 per cent, 

 all the nitrogen was active, or could be made readily available. 



One per cent of cellulose, in the form of finely divided or ground 

 filter paper, is added to soil sieved through a 2-mm. sieve. After 

 carefully mixing the paper with the soil the proper amount of moisture 

 is added. At the end of the incubation period, the soil is air dried and 

 the amount of cellulose left undecomposed determined by extract- 

 ing with Schweizer's reagent (see p. 431). Stable manure was found 

 to have a decided effect upon cellulose decomposition in the soil, es- 

 pecially when the moisture content is satisfactory. The influence of 

 reaction is not of great importance in cellulose decomposition and lime 

 serves merely in adjusting the reaction. The favorable influence of 

 manure is due to the nutrients present, especially the nitrogen. The 

 greater the amount of nutrients (nitrogen and minerals) present in 

 the manure, the greater is its favorable influence. The poorer the 

 soil is, the greater is the influence of the manure. When ammonium 

 sulfate and manure containing the same amount of nitrogen were added 

 to the soil, the stimulating effect upon cellulose decomposition was 

 found to be the same. 34 



These facts, namely that the cellulose decomposing power of a soil 

 depends more upon the physical and chemical conditions of the soil, 

 especially the available nitrogen, rather than upon a specific microbial 

 flora can be readily explained when the activities of microorganisms 

 concerned in cellulose decomposition in the soil are considered. 



As pointed out above, cellulose is decomposed in normal soils largely 

 by various fungi and aerobic bacteria. Only in soils saturated with 

 water do the anaerobic bacteria become active in cellulose decomposi- 

 tion. The ratio between the amount of cellulose decomposed and the 

 amount of nitrogen assimilated is about 30:1 in the case of fungi and 

 aerobic bacteria; however, in the soil, when the cells of microorganisms 

 freshly synthesized are constantly decomposed by other organisms, the 

 ratio is 50-60:1. In other words, for every unit of nitrogen that can 

 become available in the soil in a definite period of time, about 50 to 

 60 units of cellulose will be decomposed. If one gram of cellulose in 

 the form of ground filter paper were added to 100 grams of soil, then 



34 Charpentier, C. A. G. Studien fiber den Einflusz des Rindvieh und Pferde- 

 stallmistes auf die Zersetzung der Zellulose in der Ackererde. Inaug. Diss. 

 Helsingfors. 1921; Barthel, Chr., and Bengtsson, N. Bidrag till fragen om 

 Stallgodselns verkningssi'itt vid cellulosasonderdelningen. 1. Akerjorden. 

 Meddl. No. 248, Centralaust. Forsoksv. Jordbrucks. Bakt. Avdel. No. 29. 



