Mineralization of Organic Nitrogen Derived from Soil and from Rice-Straw-Applied Soil and Transfer from Mineralized Nitrogen to Assimilation and Denitrification

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  • 稲わら施用土壌における土壌および稲わら由来無機化窒素発現量とその有機化量の推移
  • イナワラ セヨウ ドジョウ ニ オケル ドジョウ オヨビ イナワラ ユライ ム

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Mineralization of organic nitrogen derived from soil and from rice-straw-applied soil and transfer from the mineralized nitrogen to assimilation and denitrification in the aerobic incubated paddy soil by using the ^<15>N tracer technique were examined. Two types of plots were set up: a non-rice-straw-application plot (abbreviation: OAP); rice-straw-application plots (RSAP) (i. e., 2 subplots, ^<14>N-RSAP and ^<15>N-RSAP). Soil without air-drying was incubated at 30℃. The amount of rice-straw-applied was 1.8g in 200g of soil. At the first time in a given period (for a week in this paper), each tracer NH_4-^<15>N was applied to OAP and ^<14>N-RSAP. Each NH_4 existing and its ^<15>N at the last time was determined. The results obtained were as follows: 1) The rate of N-mineralization derived from soil in RSAP showed a smaller amount than that in OAP from 3rd to 5th week after rice-straw application. The amount was 1.9 mg in OAP and 0.5mg/week in RSAP at 4th week after application. From 6th to 8th week after application, however, the former showed a greater amount than the latter. The amount was 1.8 mg in OAP and 3.3 gm/week in RSAP at 7th week after application. At 9th week after application, the amount of these two plots was equal to 1.4 mg/week. 2) The rate of N-mineralization derived from rice straw was kept nearly constant. The amount in a week was 3-5% (3-5 mg) of nitrogen in the rice straw. 3) The rate of N-assimilation derived from soil in RSAP showed a greater amount than that in OAP in the early periods. But at 4th week after rice-straw application, the former showed a smaller amount with a decrease of its amount of N-mineralization. The rate of N-assimilation derived from rice straw in RSAP was kept nearly constant. The amount was about 3% of nitrogen in rice straw. 4) The rate of denitrification derived from soil in OAP increased in the process of time. The amount was 0.33 mg/week at first week and 1.3 mg/week at 9th week after application. The amount of that in RSAP was only 0.09 mg/week at first week.

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