DYNAMICS OF AVAILABLE NITROGEN IN PADDY SOILS : II. Mineralized N Of Chloroform-Fumigated Soil as a Nutrient Source for Rice
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概要
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Rice plants were grown without N fertilizer in concrete pots (1.5m×1.5m), which were previously planted to rice or kept fallow after applying ^<15>N-labelled fertilizer. The balance of N and ^<15>N during two consecutive rice cropping seasons was calculated to analyze the dynamics of N transformation among various soil N pools, rice plant, and aquatic weeds. At harvest of the first crop, 79-83% of N in the rice plant was derived from soil N. The ^<15>N atom % excess absorbed by rice in the first crop showed an almost exponential decrease. In the early period, NH_4^+ -N in soil had a ^<15>N abundance similar to N absorbed by rice. In the middle and later periods, NH_4^+-N content became null, and its ^<15>N abundance reached approximately the natural ^<15>N level. In the early period, however, the ^<15>N abundance of MinNacf (mineralized N of chloroform-fumigated soil during anaerobic incubation) in the planted plots was lower than that of N absorbed by rice, but it became close to the ^<15>N content of the N absorbed by the plant in the middle and later periods. These findings suggest that MinNacf was a direct source of N for rice after NH_4^+-N in the soil was exhausted, and could thus be calledavailable N. Recovery of ^<15>N in plant and soil in the first crop harvest was high (80-99%) except in the Luisiana and Maahas fallow plots where a large amount of NH_4^+-N remained in the soil till harvest. The ^<15>N in MinNacf was 11-18% of the value of applied ^<15>N at this time. The ^<15>N abundance in the aquatic flora was close to that of MinNacf in the 0--1cm layer of soil. The ^<15>N abundance in blue-green algae was significantly lower than that in other aquatic weeds. Through the second cropping season, little NH_4^+-N was found in all the soils. Growth of rice and aquatic weeds was affected by previous crop conditions. the decrease of NH_4^+-N and MinNacf during crop cultivation accounted for 18-35% of ^<15>N taken up by the plant. The ^<15>N abundance of MinNacf was almost constant during the second cropping season. the amount of MinNacf and N taken up by rice under N-deficient conditions in the two cropping was highly correlated (r=0.885*), supporting the hypothesis that MinNacf is a major source of N for rice under these conditions.
- 社団法人日本土壌肥料学会の論文
著者
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Watanabe Iwao
The International Rice Research Institute
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Inubushi Kazuyuki
The International Rice Research Institute
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