时间序列方法是研究土壤发生特性演变的重要途径,而比较土壤变化的重要前提之一是序列中的土壤具有相同的起源,即具有母质的相对均一性。本研究根据史料记载中浙江慈溪海塘修筑年代估计出水稻土的耕作年龄,选择了植稻年龄约为50、300、500、700、1000a以及一个未垦滩涂剖面组成的一个时间序列作为研究对象。利用各种土壤属性参数对该时间序列的母质不连续性(或母质均一性)以及水稻土相对年龄进行了判定和验证。结果表明,时间序列的6个剖面虽然具有微小的差异,但其剖面内与剖面间母质来源相同。在水稻土母质不连续性判定中,去除黏粒的粉粒与粉粒中稳定元素Ti/Zr比值具有较好的指示作用。相对易变的土壤属性参数如碳酸钙、磁化率以及游离铁的剖面分异程度在水稻土相对年龄的判定中具有较好的指示作用。综合这些参数在时间序列中的演化趋势,发现500a剖面与整个序列的变化趋势不相符合,可能是利用历史的差异所致,在相关的性质演变研究中应该从序列中剔除。
Soil chronosequence is a valuable means in investigating rates and directions of pedogenic evolution. A soil chronosequence consisting of one tract of mudflat and five paddy soils of different rice cultivation ages were selected for this study. Ages of the paddy fields were estimated according to the literature available indicating the time when the polder was built up to reclaim the mudflat into paddy fields. The objectives of this study were to evaluate lithologic discontinuity (LDs) of the parent material in the inter-and intra-profiles of the chronosequence, and to verify relative ages of the fields by making use of various soil attribute parameters. Results show that low variation coefficient was associated with clay-free silt and Ti/Zr ratio of the silt fraction between horizons, suggesting no LDs in the studied profiles, that is to say, the profiles of the chronosequence have developed from a relatively homogeneous parent material. The clay-free silt and Ti/Zr ratio of the silt fraction are the most useful parameters in identifying LDs in this study. In order to establish a well-dated chronosequence, CaCO3 content, magnetic susceptibility and differentiation degree of free iron oxide in the profiles were used to assess soil relative ages and they were shown as good indicators of soil age and development. However, these parameters in the 500a soil profile have an odd tendency along the sequence, so it should be excluded from the chronosequence when a reliable comparison of soil changes is desired.