Soil organic matter is the basis of soil fertility, and also controls the balance of CQ2 in the atmosphere and the environmental behavior and biological effectiveness of nutrients, heavy metals and persistent organic pollutants (POPs) in Earth' s surface environment. Therefore, it is necessary to pay attention to the process of stability of organic matter. This paper dealt with the mineralogical mechanism of soil organic matter stability by studying the crimson soil profile in Conghua, Guangzhou City. The following processes were carried out: determination of the basic properties of the soil, including pH and mechanical components; determination of total organic matter content and stable organic matter content by potassium dichromate oxidation; determination of the mineral stable organic matter content by TOC analyzer; extraction of free iron oxide with dithionite-sodium citrate; extraction of amorphous iron oxide with ammonium oxalate buffer; determination of iron content by atomic absorption spectrophotometry; XRD semi-quantitative determination of the composition and content of clay minerals; and the correlation analysis between organic matter and mineral. The results indicate that the content oftotal organic matter, stable organic matter, mineral stable organic matter and recalcitrant organic matter is reduced with the increase of depth. Mineral stable organic matter is mainly existent in the middle layer of soil, while iron oxide minerals mostly occur in the upper soil. The content of kaolinite is dominant (58.7% ~84%), the content of smectite is relatively high (8.5% ~ 16.8%); besides, there exists much gibbsite. The content of smectite decreases with the increasing depth, whereas the content of kaolinite and gibbsite increases with the decreasing depth. The correlation between organic matter content and iron oxide mineral is much higher than that between clay mineral and gibbsite. Soil organic matter content and amorphous iron content are much better than the free iron content in the correlation. For instance, there is positive correlation between organic matter and amorphous iron (R2>0.9), there is positive correlation between organic matter and smectite (R2 = 0.6971), and there is negative correlation between organic matter and kaolinite, gibbsite [R2(kaolinite) = -0.681 2,R2 (gibbsite) = -0.049 8]. Obviously, the amorphous iron plays a vital role in the stabilization of soil organic matter; nevertheless, the specific surface area of amorphous iron will limit the capacity of the soil C sequestration, and the adsorption capacity will gradually become smaller until saturation. So we should pay more attention to the mineralogical mechanism of soil organic matter stability and influencing factors.%以广州市从化的赤红壤剖面为研究对象,系统测定了土壤的pH值和机械组成,土壤剖面中有机质含量、氧化铁矿物和粘土矿物的含量及分布特征,并进行了相关性分析.研究结果表明,赤红壤剖面的总有机质、稳定有机质含量、矿物稳定有机质含量和生化稳定有机质含量的变化趋势在整体上是一致的,均随深度的增加而降低.其中,矿物稳定有机质主要存在于土壤剖面的中间层,氧化铁矿物则大都集中在土壤剖面的中上层；赤红壤剖面各层位中高岭石含量都占绝对优势,为58.7％ ～84％,蒙脱石的含量次之,为8.5％ ～16.8％,除此之外,还含有较多的三水铝石.蒙脱石的含量随深度增加而降低,高岭石和三水铝石的含量随深度增加而升高.土壤有机质与氧化铁矿物的相关性较之与粘土矿物、三水铝石要大得多,有机质含量与无定形铁含量的相关系数均高于0.90,与蒙脱石、高岭石、三水铝石的相关系数分别为0.697 1、-0.681 2、-0.0498,可见无定形铁在土壤有机质稳定中起着重要作用,提醒应更加关注土壤中有机质碳库稳定锁定中的矿物学机制及其影响因素.
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