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

本研究旨在阐明土壤有机氮在短期和长期内的数量动态和结构变化过程。1.固定态氮的示踪：在730天的培养期间，研究了土壤中来自尿素的各种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的校正方法，得到了初始腐植酸和胡敏素N的表观半衰期分别为0.6和3.8年，在所有组分中，多肽/酰胺-N是主要的N物种，占59-90%，N组分没有明显的变化。因此，腐殖化过程如芳香氮的形成并没有推进，腐殖酸和胡敏素N的半衰期差异可能是由于存在/不存在与土壤颗粒的强烈相互作用所致。2.利用自然氮丰度(δ)估算土壤有机氮的中期积累速率(…)：成功地估算了累积量连续施化肥6~15年的三个旱地土壤或有机氮随时间变化的肥料衍生土壤或有机氮的增加速率和固定态氮的平均滞留时间(δ)。HA-N的长期结构变化：以腐殖化度为指标，通过土壤之间的比较来评价HA-N的长期结构变化。用XPS和15&gt；N CPMAS核磁共振仪分析了N的组成。芳香族氮和多肽/酰胺态氮占总氮的比例与腐殖化程度呈正相关和负相关，芳香族N和C的相对丰度与芳香族氮在酸解中的稳定性最高呈正相关。在热化学分解产物的GC/MS分析中只检测到吲哚、脯氨酸和三嗪类化合物。根据腐殖化度与C年龄的关系，估算出芳香氮以0.03%的速率增加，而酰胺氮则以0.05%的速度减少。较少

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