CHAPTER XVII 



Chemistry of Decomposition of Non-nitrogenous Organic Matter 

 by Soil Microorganisms 



Composition of vegetable organic matter. Vegetable organic matter 

 is added to the soil in the form of green manure, stable manure, 

 plant residues and roots of cultivated and wild plants. This organic 

 matter consists largely of celluloses, hemicelluloses and pentosans, 

 starches and other complex carbohydrates; lignins and compounds of 

 these with carbohydrates; simple carbohydrates; complex proteins, 

 protein degradation products and purine bases; fats, waxes, glu- 

 cosides, tannins, pigments and mineral matter. A typical analysis of 

 a series of native vegetable substances is given in table 31, in per cent 

 of water-free substance. 1 



However, the composition of the organic materials varies with the 

 degree of ripening of the plant, as shown 2 in table 32 for oat straw. A 

 decrease in nitrogen content and an increase in content of lignocel- 

 luloses depresses the rapidity of decomposition of the plant materials 

 in the soil, as shown later (p. 459). The elementary composition of 

 some typical plant products, on the basis of several analyses is given 

 in tables 33 and 34. 



The difference in analysis reported by different investigators is due 

 to differences in the plant varieties, in the composition of the soil, age 

 of plant, error of manipulation, etc. 



Chemistry of celluloses. The constituents of cell membranes can be 

 generally classified into five groups:^ 4 



1. True celluloses, or the condensation products of glucose, not acted upon 

 by dilute acids. 



1 Pringsheim, H. Die Polysaccharide. 2nd Ed. 1923, Berlin. 



2 Berry, R. A. Composition and properties of oat grain and straw. Jour. 

 Agr. Sci., 10: 358. 1920. 



3 Tollens, B. "Dber Cellulose, Oxycellulose, Hydrocellulose, die Pektinkorper, 

 sowie Traganth. Ber. deut. chem. Gesell., 34: 1434-1441. 1901. 



4 Heuser, E. Lehrbuch der Cellulosechemie. 2 Aufl. Berlin, Borntraeger. 

 1923. 



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