Study on the nutrient accumulation process during the initial soil formation Process

本研究旨在研究土壤形成初期的养分积累过程。研究地为宫古岛，岛上的植被及其原始演替有较好的记录，不同年代的岩屑沉积形成土壤的初始过程具有典型特征。结果表明：1)1983年、1962年、1940年、1974年和1000多年来，随着A层厚度的增加，1874年以前的A/C剖面发育为未成熟土，100多年来，A层发育成形成层，属于棕森林土。2)通过粒度分布、pH值、水溶性碱和交换性碱的分析，发现：5个代表性土壤剖面各层土壤样品的总碳、总氮、CEC、草酸盐可提取的Al、Fe、Si和粘土矿物组成，以及在炉渣形成土壤初期养分积累的特征。(1) 2 mm以上的粒级含量减少，粉砂粒级和粘土粒级的总和从0.8%增加到48%。土壤有机质的积累过程从地表水平的0.04%增加到9.15%。此外，粘土组分的性质仍然是无定形的，但草酸盐可提取的Al+1/2Fe的量明显增加。由于这些增加以持续时间的对数表示，CEC也从0.64增加到21.75 cmolc/kg，与水溶性和交换性碱（Ca, Mg， K, Na）的增加相对应，特别是后者，这支持了在土壤形成早期所研究的这类土壤的碱饱和度接近100%的特征。(2)水和1N KCl萃取的有效磷、硝态氮和铵态氮离子也随CEC的增加而增加。综合以上结果，在世界范围内首次估算了约1000年原始演替过程（从山渣裸地到栲林顶极）下的土壤养分积累速率。少

This study aims to investigate the nutrients accumulation process in the initial soil formation process. Study field was Miyakejima Island where the vegetation and its primary succession is well documented and typical initial soil formation process from scoria of different age of deposition. The results obtained are as follows :1) According to the soil survey on the scoria hills of 1983, 1962, 1940, 1974 and more than 1000 years, the development of soil profiles shows A/C profile up to 1874 with increasing the thickness of A horizon, classified as Immature Soils, while cambic Bhorizon is developed on the scoria hill of more than 100 years, classified as Brown Forest Soils.2) Based on the analyses for particle size distribution, pH, water-soluble and exchangeable bases, total carbon and nitrogen, CEC, oxalate-extractable Al, Fe, Si, and clay mineral composition on the soil samples from each horizon of 5 representative soil profiles, the following characteristics of nutrient accumulation … More during the initial soil formation process from scoria.(1) The fraction of more than 2 mm decreased, while sum of silt and clay fractions increased from 0.8 % to 48 %. And, accumulation process of soil organic matter is increased from 0.04 % to 9.15 % in the surface horizon. Moreover, nature of clay fractions is still amorphous, but the amount of oxalate-extractable Al+1/2Fe apparently increased. Due to these increases expressed as logarithm of the duration of time, CEC also increased from 0.64 to 21.75 cmolc/kg corresponding with the increase in water-soluble and exchangeable bases(Ca, Mg, K, Na) especially in the latter, which support the base saturation degree of nearly 100 % characteristic for this kind of soils studied in the early stage of soil formation.(2) Available phosphorus and nitrate and ammonium ions extracted with water and 1N KCl also increased, showing the similar tendency with the increase in CEC.From all results obtained above, it can be concluded that the rate of nutrition accumulation in the soils under the primary succession of about 1000 years (from bare land of scoria to climax of Castanopsis forest) is estimated for the first time in the world. Less