Influence of different land use on the soil morphology and physico-chemical properties of andosols: comparison of deciduous forest soils and cultivated soils in the musashino area, Tokyo

摘要

It has been about 350 years since a different land use started as a deciduous forest land and cultivated land reclaimed from wild grassland in the Musashino area of Tokyo. We studied the characteristics of soil morphological and physico-chemical properties in the adjacent Andosols that have been continued the different land utilizetion in this area.In the forest soil morphology, a blackish soil color increased in all horizons and developed toward the bottom of the profile compared to cultivated soils, due to the accumulation of humic substances derived from fallen leaves in the topsoil and the percolation of humic substances through deteriorated root cavities to the ower horizons.Reflecting the soil morphological characteristics, the levels of humus content in all horizons of the forest soil was higher than those in the cultivated soils. The C/N ratio in the forest topsoil was higher than that in the deeper horizons, since it received more fresh fallen leaves every autumn. The ratios of all horizons in the forest soils were higher than those of the cultivated soils, due to the accumulation of immatured humic substances in the deeper horizons by percolation.According to the humus content, the levels of CEC in all horizons of the forest soil was higher than those in the cultivated soil. On the other hand, the levels of exchangeable cations or base saturation of the cultivated soil had a higher tendency in comparison with the forest soil due to the dressing of inorganic soil amendment to the cultivated land. In the plow layers of the cultivated lands, the base saturation was lower than that of the sub soils owing to the absorption of bases by the planting crops. In the case of continuous removing of the fallen leaves, the base saturation of the topsoil in the place was lower than that of other topsoils of the forest land.The concentration of available phosphate in the plow layers of the cultivated land was seven times higher, at a minimum, than in the topsoil of the forest land and it was the most distinguishing variation in the content of the chemical elements in the cultivated soil in comparison with the forest soil. The increase in the available phosphate showed a history of improvement of the Andosols to enable for the crop production in this area.Owing to the accumulation of flesh organic matter on the surface of the forest land, a humic substance which had a lower degree of humified humic substances accumulated in the topsoil in comparison with second topsoil. Whereas all horzons of forest soils had a higher degree of humified humic composition compared with the cultivated soil. The humic acid in the plow layers had a lower degree of humified humic acid in comparison with the topsoils of forest land. This result suggested that a lowering of humification occurred from a decomposition of the original humic acid to lower molecular humic acid due to the plowing.The characteristics of soil sugar composition showed that the topsoils of the forest lands had a high content of mannose and cellulose type glucose, which might originate mainly from microorganisms and plant remains, respectively. Thereas, the level of cellulose type glucose was lower in the plow layer. Those results suggested that the fresh organic matter and the population of microorganisms were rich in the topsoils of the forest land, on the other side, the amount of fresh organic matter to the plow layers was much less than that on the forest lands.