EVIDENCE FOR MICROBIAL DECOMPOSITION OF ORGANIC-ACIDS DURING PODZOLIZATION

Microbial aspects of podzolization were studied by percolating organic acids through sterile and non-sterile soil in columns. Six columns co ntaining sand from a fluvioglacial sediment were percolated (90 mm d(- 1)) with mor extract and an oxalate-citrate solution. In three of thes e, sterilized soil solutions were used. Weathering was enhanced by org anic acids which formed complexes with aluminium and iron. In the non- sterile soil columns weathering by organic acids was inhibited at 7-8 cm because the acids were degraded by microorganisms. Weathering was e vident from colour change, contents of extractable aluminium and iron, and the micromorphology. Enhanced weathering in the sterile columns w as also suggested by larger amounts of aluminium, iron, silica and bas e cations leached from the columns. Comparison of the output of alumin ium, iron and silica from the sterile soil with that from the non-ster ile soil, suggests that probably an aluminium-iron-silicate phase was formed in the deeper parts of the non-sterile columns.