A Comparative Study of the Effect on Barley Growth of Humic Substances Extracted from Municipal Wastes and from Traditional Organic Materials

Abstract

The effect on barley growth of humic substances extracted from municipal wastes with different degree of stability was studied. This effect was compared with that of the humic substances extracted from organic materials used in industry to obtain humic acids (peat and leonardite). The humic substances extracted from municipal wastes had higher aliphatic character, lower oxygen group content and a more heterogeneous composition than the humic substances from peat and leonardite. All humic substances, regardless of their origin, nature and characteristics increased plant yields (from 38 to 62% of the increase) and macronutrient absorption with respect to the control when they were added at different amounts (5, 100 and 200 mg C kg−1) to a calcareous soil. This increase was highest with the humic substances from municipal wastes, which in turn had the greatest positive effect on the absorption of nitrogen and phosphorus up to 74% increase of N and 72% increase P with sewage sludge HS at 200 mg C kg−1 by barley plants.