CHARACTERIZATION AND EVALUATION OF HUMIC ACIDS EXTRACTED FROM URBAN WASTE AS LIQUID FERTILIZERS

In this work a comparative study of humic acids extracted from organic wastes(sewage sludge and compost) and those currently used in the hum ic acid companies (humic acids from leonardite and peat) was carried o ut. Humic acids were characterised by means of chemical analysis (elem ental and functional analysis) and spectroscopic techniques (C-13 NMR, gel filtration and infrared spectra) in order to relate their charact eristics with their effect on plant growth. Chemical and spectroscopic analysis emphasised the different nature of the studied humic acids. The humic acids derived from the less evolved organic materials (sludg e and compost) showed higher aliphatic nature, higher nitrogen compoun d content, lower oxidation degree and more heterogeneous composition t han those extracted from more evolved materials (peat and leonardite). However, all these differences did not lead to significant difference s in plant growth, but all these humic acids showed an increase of the yield respect to the control.