Humic acids (HA) were extracted from sheep (SH), cow (CO), goat (GO) and rabbit (RA) manures which were vermicomposted with the earthworm Eisenia foetida. HA DSC curves showed well-defined thermal events indicative of intramolecular bonds (300 ºC) and intermolecular organo-mineral linkages (500 ºC). All samples showed high nitrogen contents (from peptide chains and probably N-heterocycles) and aromatic and/or unsaturated aliphatic conjugated structures, as well as a low carboxylic functionality content. The SH-HA was the most similar to a medium soil HA and the RA-HA being the least similar. The results show that it is possible to prepare distinct worm-composts to solve specific problems of degraded soils.
humic acids; vermicomposts; thermal analysis; acid groups of humic substances
