Chemical nature of the soil mineral fraction: the importance of clays and cations

The biological stability of soil organic carbon (SOC) is influenced by the chemical structure of SOC and the existence of various mechanisms of protection offered by soil minerals and their spatial arrangement within the soil matrix (Baldock and Skjemstad, 2000). In addition to defining the potential availability of SOC to decomposer organisms living in soils, the chemical structure of SOC also defines the strength with which mineral and organic soil components interact. The degree of physical protection of SOC is mainly a factor of soil texture, specific mineral surface area, and soil mineralogy. However, other soil parameters (e.g. water holding capacity, pH, porosity) can act as rate modifiers in attaining the protective capacity, set by the mineral matrix of the soil. Therefore, maximum protective capacity can only be achieved under “ideal” conditions because other soil properties, together with the parameters established by the soil mineral matrix, affect whether carbon will accumulate in soil up to its maximum capacity. Thus, a realistic assessment of the degree of protection of SOC by soil minerals is possible only through a collective analysis of the individual physical, chemical, and textural properties of a soil. Bearing these limitations in mind, the aim of this paper was threefold: