Development of models expressing time-dependent structural variations of soil organic nitrogen

旨在阐明土壤有机氮在短期和长期的定量动态和结构变化过程。在730天的孵育期内，研究了固定^<15>N-尿素产生的各种土壤有机氮组分的数量和组成随时间的变化。建立了微生物生物量污染校正方法，获得了初始腐植酸（HA）和腐殖素N的表观半衰期分别为0.6和3.8年，各组分中以肽/酰胺态氮为主，占59 ~ 90%，氮组成无显著变化。因此，腐殖质化过程如芳香N的形成并没有推进，HA和human N半衰期的差异可能是由于是否存在与土壤颗粒的强相互作用。利用自然氮丰度（δ ^<15>）估算土壤有机氮中期积累速率：利用δ ^<15>随时间的变化，成功估算了连续施用化肥6 ~ 15年3个旱田土壤有机肥累积速率和固定态氮平均停留时间。同样的方法也适用于HA-N，所得值与^<15> n示踪剂实验的估计值一致。HA- n的长期结构变化：以腐殖化程度为指标，通过土壤间比较，评价了HA- n的长期结构变化。用XPS和^<15>N CPMAS NMR分析了N的组成。芳香族氮和肽/酰胺氮在总氮中的比例与腐殖化程度呈正相关和负相关，芳香族氮和碳的相对丰度呈正相关，芳香族氮在酸水解中的稳定性最高。在GC/MS分析中仅检测到吲哚、脯氨酸和三嗪化合物。根据腐殖化程度与^<14>C-age的关系，估计芳香- n以0.03%的总- n y^<-1>的速率增加，酰胺- n以0.05%的总- n y^<-1>的速率减少。少

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