農学部

Decomposition of organic nitrogenous materials in soil was affected by C/N ratio.Immobilization of nitrogen mineralized from nitrogenous material added to the soil was influenced by the degradability of carbonaceous and nitrogenous materials.The turnover of nitrogen which had been freshly immobilized in the presence of glucose in the soil was faster than that immobilized with cellulose or lignin. The effect of soil-drying on the mineralization of organic nitrogen immobilized through the decomposition of carbonaceous and nitrogenous materials in the soil depended significantly on the availability of carbonaceous materials as a microbial energy source.However, the drying effect was not always proportional to the amount of organic nitrogen accumulated in the soil.

Phenolic compounds in the soils collected from plow layers of greenhouse and field cultures were surveyed quantitatively by gas chromatography. The results are as follows : 1) p-Coumaric, ferulic, salicylic, p-hydroxybenzoic, vanillic, syringic, and protocatechuic acids were detected in all upland soils, as in the case of paddy and forest soils reported previously. Among these phenolics, p-coumaric acid was present in the largest quantity in most of the upland soils up to 29.0 ppm. 2) The total amounts of individual phenolic acids in the upland soils ranged from 9.5 to 62.0 ppm (average 26.0 ppm). Also, the amounts were less than 0.18% (average 0.10%) of the total soil organic matter. The average values in the upland soils were higher than those in the paddy soils, but were lower than those in the forest soils. 3) In upland soils, the concentrations of p-hydroxybenzoic, vanillic, syringic, p-coumaric, and ferulic acids, which have no chelating ability, were considerably related to the carbon content of soil, but the concentrations of protocatechuic and salicylic acids, which are chelating agents, were not related to that of soil. These relationships agreed with those found in paddy and forest soils.