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

本研究对湿润热带土壤有机质（SOM）动态进行了研究，得到的主要结果如下：1)原位测量了土壤有机质动态，并对土壤温度、湿度等环境条件进行了详细监测，确定了湿润热带各地区土壤有机质动态的主要控制参数；研究区域包括：日本天然林、印度尼西亚不同母质的天然林、泰国北部克伦人的流动农田和休耕林、泰国东北部的沙质农田和印度尼西亚不同的家庭花园。2)为了优化区域轮作制度，以泰国东北部沙质农田为研究对象，利用地理统计学方法分析了土壤有机碳动态的时空变化。土壤有机碳、氮含量、粒径分布及其他相关性状具有明显的空间差异。SOM动力学和土壤侵蚀被认为是土壤性质异质性背后的驱动力。研究结果还表明，地统计学方法可以在考虑土壤资源空间异质性的区域尺度上模拟土壤动力学。3)确定了湿润热带不同地区土壤相关参数对土壤有机质动态的控制作用。东加里曼丹地区轮作田的碳氮动态受土壤酸度的影响。火山衍生的土壤性质（或半氧化物的非晶性质）也强烈地控制了所研究的不同土壤的SOM动力学。4)因此，即使在潮湿的亚洲有限地区，SOM的分解速率也有很大差异，这不仅取决于气候条件，还取决于与颗粒大小和/或无定形特征有关的土壤性质，后者反映了气候（即凉爽）和地质（即火山起源）条件。土壤酸度可以以不同的方式影响碳通量；即通过改变分解速率常数和分解同化的分裂比，或在土壤剖面中形成向下迁移的DOC。有些情况是潮湿热带地区特有的。因此，在建立可实际应用于湿润热带生态系统的SOM动力学模型时，应考虑这些条件。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