Soluble aluminium- and iron-organic complexes and carbon cycle in Hapludaffs and Haplorthods under forest and cultivation

Abstract

In loamy Hapludalfs and sandy Haplorthods under forest and cultivation, the annual C, Al and Fe balances are presented in order to indicate element transfer into the subsoil. Aluminium and iron in the soil solution are separated into inorganic and organic fractions. In the Typic Hapludalf under forest initial podzolization is documented by an increase in Al release, its translocation into the subsoil and soil acidification. The Al3+ concentration is 2.7 mg l−1 and probably phytotoxic. The Hapludalfs under cultivation are influenced by stagnant water and the main part of iron is translocated in iron-organic complexes from the Bt into the subsoil. The aluminium release and transfer is minimal. In one Hapludalf erosion hinders an accumulation of humus, in spite of a C surplus. Extensive soil management in the forest and intensive cultivation without application of manure are incompatible with soil protection. In a Typic Haplorthod under spruce, podzolization is documented by the translocation of carbon and especially aluminium. A low pH induces weathering of soil minerals with a high release of Al3+ and its translocation into the subsoil. Its concentration in the topsoil is extremely phytotoxic. In a similar Typic Haplorthod under cultivation the carbon and metal sink (Bh/Bhs) is being decomposed and has become a source of carbon and iron-organic complexes; these are translocated into the subsoil. The natural accumulation process has been reversed by man.