抄録
Some fresh-water algae and weeds spontaneusly developing in the paddy field were analysed for their chemical constituents and decomposed in the soil, chiefly intended to suggest how far they are responsible for the circulation of the fertilizer nitrogen. The results may be summarized as follows : - 1. Two species of film-forming algae, Euglena sp. and Pleurococcen sp., and a sort of Lemnacea, Lemna paucicostata Hegelm, were artificially developed in the water-logged soil fertilized with 60 mg nitrogen (as ammonium sulfate) per pot. At their maximum development (after 21 days culture) the total nitrogen absorbed and converted into organic form by the algae and lemna reached 6.08〜15.28 mg per pot. 2. Six sorts of algae and weeds, i. e. Hydrodictyon sp., Spirogyra sp., Euglena sp., Lemna paucicostata Hegelm, Hydrilla verticillata Casp var Roxburghii, Najas graminea Delile, commonly observed in abundant development at the Konosu experiment field, were collected and analysed for the amount of organic and inorganic constituents. For the determination of organic materials the proximate method proposed by WAKSMAN and STEVENS was conveniently used. The total nitrogen content varied from 2.20 to 6.62 % dry weight, and carbon-nitrogen ratios from 20.1 to 6.6. The water-soluble nitrogen content showed fairly good proportionality to the total nitrogen content. It is of interest in connection with the later mentioned decomposition study, that the content of the lignin, reported by many workers to be considerably resistant to bacterial attack and recently suggested by WAKSMAN to play an important role in the formation of soil humus, was fairely low and fluctuated from 2.91 to 6.18 % dry weight. 3. The aforenamed six samples were respectively decomposed in the soil under both paddy field and dry farm conditions and examined on the mode of nitrogen mineralisation. Under paddy field condition the ammonia accumulation at the earlier stage of decomposition proceeded with greater rapidity as the carbon-nitrogen ratio was narrower. As the mineralisation progressed further, however, the samples of wider carbon-nitrogen ratio appeared to recover the power of ammonia formation and in view of the maximum ammonia accumulation they were even comparable with those of narrower carbon-nitrogen ratio. Under dry farm condition the nitrate formation was more effective as the carbon-nitrogen ratio was narrower during the whole period of experiment and showed close agreement with the width of the carbon-nitrogen ratio. Moreover, a brief description of the distillation apparatus was conveniently given, which one of the authers SHIOIRI proposed for the determination of ammonium-nitrogen in the soil, devised after the micro distillation apparatus of PARNAS and WAGNER.
