The biological decomposition of plant materials

THE decomposition of plant materials in the soil or in compost heaps involves the assimilation of the carbohydrate constituents of the tissues and the con- version of available nitrogen to microbial protein by the organisms concerned. In nature the supply of nitrogen is often a limiting factor in determining the rate and extent of decomposition. Mature plant tissues frequently contain rather a low percentage of nitrogen, and to effect a complete and speedy rot, an additional quantity of available nitrogen has to be supplied. If too much is provided, losses occur, or if too little, the decomposition is incomplete unless an unusually long period of time is allowed. Hutchinson and Richards 1921 were the first to recognise the quantitative importance of nitrogen in decomposition, and they determined the amount necessary for the decom- position of a number of materials. For common straws, for example, they found it to be between 0 7 and 0-8 g. nitrogen per 100 g. original material. This figure they termed the "nitrogen factor." It may be defined as the additional inorganic nitrogen immobilised as organic nitrogen by 100 g. of any material in the process of decomposition. This quantitative relationship forms the basis of Richards and Hutchinson's patents 1924 for the production of "artificial farmyard manure " (Adco), from waste plant materials. The " nitrogen factor " gives the maximum amount of nitrogen which when added to decomposing material will be retained without loss.