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

本研究对湿热带地区土壤有机质（SOM）动态进行了研究，取得的主要成果如下：1）原位SOM动态测量，结合土壤温度、湿度等环境条件的详细监测，确定了湿热带各地区SOM动态的主要控制参数。这些区域包括：日本天然林、印度尼西亚不同土壤母质的天然林、泰国北部克伦人使用的轮耕田和休耕林、泰国东北部的沙地农田以及印度尼西亚的不同家庭花园。 2）为了优化区域轮作系统以减轻 SOC 损耗，利用生物统计学技术对泰国东北部沙地农田的 SOM 动态时空变化进行了分析。土壤有机碳和氮含量、粒径分布和其他相关特性观察到明显的空间变化。 SOM 动力学和土壤侵蚀被认为是观察到的土壤性质异质性背后的驱动力。结果还表明，考虑到地形不同土壤资源的空间异质性，地统计学方法有助于在区域尺度上模拟SOM动态。3）在湿热带不同地区确定了控制SOM动态的土壤相关参数。东加里曼丹轮作田的碳氮动态受到土壤酸度的影响。土壤的火山衍生特性（或倍半氧化物的无定形特性）也强烈控制了所研究的不同土壤中的 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/或无定形特性相关的土壤特性，后者反映了气候（即凉爽）和地质（即火山起源）条件。土壤酸度会以不同方式影响碳通量；即通过改变分解速率常数和分裂比进行分解同化，或形成DOC在土壤剖面中向下迁移。其中一些条件是湿热带地区特有的。因此，在建立可实际应用于湿热带生态系统的SOM动力学模型时应考虑这些条件。较少的

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