ON THE ORIGIN OF THE URONIC ACIDS IN THE HUMUS OF SOIL, PEAT, AND COMPOSTS

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Abstract
Under the term "hemicellulose," the authors include both the true hemicelluloses (Schulze), and the polyuronides (complexes which consist of mixtures of sugars and uronic acids). A series of analyses are presented giving the abundance of pentosans, of total hemicelluloses, and of uronic acid complexes in plant materials, in composts where plant substances are undergoing active decomposition, in peats, in forest soils, and in mineral soils. Results show that in the decomposition of plant residues, the true pentosans are attacked more rapidly by microorganisms than are the uronic acid complexes. Whether these are as such more resistant to decomposition or whether they form compounds with the other chemical complexes, as lignins and proteins, which renders them more resistant to rapid decomposition, remains to be determined. Different plant materials vary in the relative concentration of the different hemicelluloses and in the relative rapidity with which these are decomposed by microorganisms. With the advance of decomposition of plant residues, there is a progressive diminution of the pentosans and a relative increase of the uronie-acid complexes. Manuring of soil results in an increase in the pentosan content; continued cultivation without addition of fresh organic manures or plant residues, results in a rapid reduction of the total soil humus and a corresponding relative increase in uronic acid complexes. The nature of the soil, its reaction, soil treatment, and system of fertilization all modify not only the abundance of the total organic matter in soil, but also its chemical composition.