A comparison between the effect of fresh and dried organic materials added to soil on carbon and nitrogen mineralization

Summary Incubation experiments were carried out at 29°C in which fresh chopped, dried chopped, or dried and ground material of wheat plants,Polygonum nodosum, Senecio congestus (R. Br. DC.) and lucerne was mixed with a heavy calcareous loam. The C/N ratios of these materials were 45.9, 32.0, 19.3, and 12.6, respectively. At intervals of one or two weeks the content of mineral nitrogen in the treated and untreated soils was determined. In this way the immobilised or released nitrogen could be calculated. Parallel to this experiment the production of CO₂ in the soils treated in the same way was determined.The experiments have clearly shown that the mineralization of the carbon and nitrogen of incorporated organic materials is influenced not only by the N-content, the C/N ratio of the materials and the amount of the materials, but also depends on whether the plant materials are in fresh chopped, or dried chopped, or dried and ground condition.In most cases a retardation of the rate of nitrogen mineralization was found after drying the organic materials due to an increase of the C/N ratio of the water-soluble organic fraction by drying. The depressing effect of drying on the rate of nitrogen mineralization was increased by a mechanical breaking-up of the dried materials, presumably due to an increased surface of the non-soluble carbonaceous compounds.