2004 Fiscal Year Final Research Report Summary
Development of models expressing time-dependent structural variations of soil organic nitrogen
| Project/Area Number |
14360040
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Plant nutrition/Soil science
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| Research Institution | Nagoya University |
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Principal Investigator |
WATANABE Akira Nagoya University, Graduate School of Agricultural Sciences, Assoc.Prof., 大学院・生命農学研究科, 助教授 (50231098)
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| Co-Investigator(Kenkyū-buntansha) |
KATAYAMA Arata Nagoya University, Eco Topia Science Institute, Professor, エコトピア科学研究機構, 教授 (60185808)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Soil organic nitrogen / Humid acids / Humin / ^<15>N tracer / Natural ^<15>N abundance / Chemical fertilizer / ^<15>N NMR / XPS |
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| Research Abstract |
The elucidation of quantitative dynamics and structural variation process of soil organic N during short to long terms was aimed.
1.Tracing of immobilized ^<15>N : Time-dependent variations in amount and composition of various soil organic N fractions derived from ^<15>N-urea were investigated in a 730-day incubation period. The method for correcting contamination of microbial biomass was developed, and the apparent half-life, 0.6 and 3.8 years, were obtained for initial humic acid(HA) and humin N. Peptide/amide-N was major N species in all the fractions, 59-90%, and no significant variations in N composition were observed. Therefore, the humification process such as the formation of aromatic-N has not advanced, and the difference in half-life between HA and humin N could be due to the presence/absence of strong interaction with soil particles.
2.Estimation of middle-term accumulation rate of soil organic N using natural ^<15>N abundance (δ ^<15>) : It was succeeded to estimate the accum
… More
ulation rate of fertilizer-derived soil or organic N and the mean residence time of immobilized N from time-dependent change in δ ^<15> for three upland fields with continuous application of chemical fertilizer for 6-15 years. Same method was applicable for HA-N, and the obtained value agreed to that estimated from the ^<15>N-tracer experiment.
3.Long-term structural change of HA-N : Long-term structural changes in HA-N were evaluated from the comparison among soils using the degree of humification as an index for years since HA formation. XPS and ^<15>N CPMAS NMR were used to analyze N composition. Positive and negative correlations between the proportions of aromatic-and peptide/amide-N in total-N and the degree of humification, positive correlation between the relative abundances of aromatic N and C, and highest stability of aromatic-N in acid hydrolysis were found. Only indole, praline, and triazine compounds were detected in GC/MS analysis of thermochemolysis products. Based on the relationship between the degree of humification and ^<14>C-age, it was estimated that aromatic-N increases at the rate of 0.03% total-N y^<-1> while amide-N decreases at the rate of 0.05% total-N y^<-1>. Less
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