Criterious preparation and characterization of earthworm-composts in view of animal waste recycling. Part I. Correlation between chemical, thermal and FTIR spectroscopic analyses of four humic acids from earthworm-composted animal manure

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 degrees C) and intermolecular organomineral linkages (500 degrees C). 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.