EFFECTS OF HUMIC ACIDS FROM COMPOST-STABILIZED GREEN WASTE OR LEONARDITE ON SOIL SHRINKAGE AND MICROAGGREGATION

Humic acids extracted from composted vegetable residues (green compost ) or mined lignite (leonardite) have been tested for their influence o n either soil cracking or microaggregation characteristics. This preli minary study has pointed out that humates from green compost, within t he range of 1000 to 8000 mg kg(-1) of soil, induce small-size clod for mation in a dose-independent manner and preserve stability of microagg regates. On the other hand, humic acids from leonardite did not improv e soil shrinkage and water-stable microaggregates, but rather they det ermined deterioration of such physical characteristics of the soil tes ted.