Studies on Soil Organic Matter Dynamics and Their Application for Sustainable Agriculture in Humid Tropics

1)对湿润热带土壤有机质动态进行了现场观测，并对土壤温度、水分等环境条件进行了详细监测，确定了湿润热带不同区域土壤有机质动态的主要控制参数。这些地区包括：日本天然林、不同土壤母质的印度尼西亚天然林、泰国北部克伦人使用的轮作农田和休闲林、泰国东北部的沙地农田和印度尼西亚的不同家庭花园。2)为了优化区域轮作制度以缓解SOC的枯竭，利用区域统计技术分析了泰国东北部沙地土壤有机质动态的时空变化。土壤有机C和N含量、颗粒大小分布和其他相关…具有明显的空间变异更多房产。土壤有机质动态和土壤侵蚀被认为是土壤性质异质性背后的驱动力。3)确定了不同湿润热带地区土壤有机质动态变化的土壤相关参数。东加里曼丹轮作农田碳、氮动态受土壤酸度的影响。土壤的火山性质(或倍半氧化物的无定形性质)也强烈地控制着不同土壤中的SOM动态。4)因此，即使在亚洲潮湿的有限地区，SOM的分解速率也有很大的差异，不仅取决于气候条件，还取决于与颗粒大小和/或无定形特性有关的土壤特性，后者既反映了气候(即凉爽)条件，也反映了地质(即火山成因)条件。土壤酸度通过改变分解速率常数和分解与同化的分流比，或形成向下迁移的DOC，以不同的方式影响土壤碳通量。其中一些条件是潮湿热带所特有的。因此，在建立可实际应用于湿润热带生态系统的土壤有机质动力学模型时，应考虑这些条件。较少

The main results obtained in the present study, in which soil organic matter (SOM) dynamics in humid tropics were investigated, are listed below:1) In situ SOM dynamics were measured together with detailed monitoring on environmental conditions such as soil temperature and moisture, and parameters that primarily control the SOM dynamics in various regions of humid tropics were determined. The regions included: Japanese natural forests, Indonesia natural forest with different soil parent materials, shifting cropland fields and fallow forests used by Karen people in northern Thailand, sandy cropland in Northeast Thailand, and different home gardens in Indonesia.2) To optimize regional crop rotation systems for mitigating SOC depletion, spatial and temporal variation of the SOM dynamics was analyzed using a giostatistics technique in sandy croplands in Northeast Thailand. A clear spatial variation was observed for organic C and N soil content, particle size distribution, and other related … More properties. The SOM dynamics and soil erosion were postulated to be driving forces behind the observed heterogeneity in soil properties. The results also indicated that the methodology of geostatistics were useful to simulate SOM dynamics in a regional scale considering spatial heterogeneity of soil resources according to topography.3) Soil-related parameters controlling SOM dynamics were determined in different regions of humid tropics. The C and N dynamics in the shifting cropping fields in East Kalimantan were influenced by the degree of soil acidity. The volcanic-derived properties of soils (or amorphic properties of sesquioxides) also strongly controlled SOM dynamics in different soils investigated.4) Thus the decomposition rates of SOM varied widely even in the limited areas of humid Asia, depending not only on climatic conditions but also on soil properties relating to particle size and/or amorphous characteristics, the latter of which reflects both the climatic (i. e., cool) and geological (i. e., volcanic origin) conditions. Soil acidity can affect C fluxes in different ways; that is, through changing decomposition rate constant and splitting ratio for decomposition to assimilation, or forming DOC that migrates to downward in soil profiles. Some of these conditions are specific for humid tropics. Therefore, these conditions should be taken into account to establish SOM dynamics model that could actually be applied to ecosystems in humid tropics. Less