Podzol formation

Podzol formation. Podzols are acidic soils of forested areas characterized by the pedogenic accumulation of iron (Fe) and aluminum (Al) in the B horizon (podzolic B horizon). Podzols cover large areas of the wet temperate and boreal zones and are associated to coarse parent materials. Knowledge on podzol genesis is of considerable interest with respect to the understanding, modelling and management of forested, agricultural and aquatic ecosystems and to the forecasting of soil changes in response to environmental perturbations. Four theories, or conceptual models, were formulated to describe podzol formation : the fulvate theory (Stobbe and Wright, 1959; McKeague at al., 1978), the proto-imogolite theory (Farmer at al., 1980; Anderson at al., 1982), the theory of chemical compartments (Ugolini and Dahlgren, 1987) and the Al polymer theory (Browne, 1995). Each theory emphasizes the role of specific processes such as the formation and transport of organo-metallic complexes, proto-imogolite synthesis and imogolite precipitation, mineral weathering by carbonic acid (H2CO3) and the formation of polynuclear Al-silicate soluble complexes. However, the relative importance attributed to any of these processes varies as a function of the properties of the sites explored by the authors of a given theory. The absence of an integrated theory of podzol genesis also reflects our incomplete understanding of podzol dynamics, the fact that important processes have been left out and the apparent opposition between theories.