CHAPTER II. 

 THE DECOMPOSITION OF ORGANIC MATTER IN THE SOIL. 



CARBOHYDRATES 



ORIGIN. The sugars, starches, vegetable gums and allied pectine 

 substances, as well as the cellulose, contained in roots and other crop 

 residues add large quantities of carbohydrates to the soil. The crop 

 residues are augmented still further by green manures and animal 

 manures whenever these are used. A good growth of timothy, for example, 

 may increase the content of organic matter in the surface soil by five 

 hundred or a thousand pounds per acre, and three-quarters of this 

 consists of carbohydrates. In the same manner, a green manure crop, 

 or an application of barnyard manure may add to the land as much as 

 fifteen hundred pounds, or even more, of carbohydrates per acre. These 

 carbohydrates contain a large proportion of cellulose. 



THE DECOMPOSITION OF CELLULOSE. Pure cellulose (C 6 H 10 O 5 ) X 

 is a rather inert substance, as exemplified by the resistance of cotton and 

 flax fiber to decomposition processes. It is well known, nevertheless, 

 that even cellulose is in the end decomposed and resolved into simple 

 compounds. Plant roots, leaves and stems, as well as the trunks of 

 fallen trees, gradually distintegrate and vanish. Under favorable con- 

 ditions this may proceed rapidly, as is indicated by the processes in septic 

 tanks, or in manure heaps on the one hand, and in open sandy soils on 

 the other. The disappearance of cellulose may be accomplished by (a) 

 anaerobic organisms, (b) by aerobic organisms, (c) by denitrifying 

 bacteria, and (d) by molds. 



THE PRODUCTION or METHANE AND HYDROGEN. The decomposition 

 of pure cellulose and the formation of methane and hydrogen mixed with 

 other gases was first noted by Popov in 1875. Some years later Tappeiner 

 and also Hoppe-Seyler confirmed Popov's observations that nearly pure 

 cellulose in the form of Swedish filter-paper, or cotton fiber may be fer- 

 mented by bacteria with the evolution of methane, carbon dioxide and 

 occasionally also of hydrogen. These investigators ascribed the decom- 



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