EFFECT OF TEMPERATURE ON NITRIFICATION IN SOILS
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概要
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Nitrification must be treated as the phenomenon comprising two parts. The one is the nitrate forming ability from ammonia by a unit cell, and the other is the process of increasing the number of nitrifying organisms. The author examined the effect of temperature on each part of nitrification by using the "washing cultivation method". As samples, use was made of three kinds of soils each of which has different characteristics in respect to nitrification activity. These were alluvial soil which has high nitrifying power, volcanic ash soil which has low power, and river-side sand which is the most feeble. The results obtained can be summarized as follows : 1) In alluvial soil, nitrifying ability reached the maximum limit most quickly at 25℃ as well as at 15℃. At 5 and 35℃, nitrification was fairly delayed, but nitrate formation was rather great. In volcanic ash soil with low nitrifying ability nitrification was more delayed within the temperature range apart from the optimum. In river-side sand, nitrifying ability did not show any increase at 5 and 35℃. 2) Soils which got high nitrifying ability at 25℃ appeared to show less nitrate formation at other temperatures than the soils which were cultivated at the same temperature from the beginning of incubation. However, more nitrate was formed at 5℃ in volcanic ash soil and sand by cultivating at 25℃ for the purpose of increasing the number of microbes. 3) From these results it is clarified that nitrification is much influenced at low temperature by the number of microbes in soils, and cultural conditions, especially temperature, exert much influence upon the increasing process of nitrifying organisms. The author is greatly obliged to Mr. T. NISHIKATA, the Head of the Department of Agricultural Chemistry, Hokkaido National Agricultural Experiment Station, for undertaking the revision of this report.
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