ИСТИНА

Humic products (HP) produced by companies from various organic materials, are being increasingly used in soil remediation. Depending on organic source material (lignite, peat or composts), humic acids (HA), which are considered to be the active ingredient in HP, are different in chemical structure and in their efficiency as plant growth promotors and soil conditioners. The objective of the study was to evaluate in a number of laboratory, pot and field experiments the potential of HP as plant growth stimulators for agriculture and as remediating agents for contaminated soils. Chemical properties of a number of lignite-, peat- and lignosulphonate- derived HP (elemental content, IR-spectra, absorption and fluorescence spectra) are analysed. Biological activity of the same HP are examined in laboratory and field experiments using various endpoints: plant biometry, soil chemical and biochemical parameters, bioassays with battery of test-cultures, effect on yield and crop quality in field trials. Potential of HP to decrease content of available species of heavy metals in contaminated soils is evaluated in case studies. Several approaches to assess the effectivity and “integrated environmental quality” of HP are tested and compared using detoxication coefficient, Triad method, and Harrington desirability function. The organic matter genesis is the key factor influencing composition and structure of HA in HP. HA from fossil coal are more aromatic, hydrophobic, contain fewer functional groups and mobile low-molecular components. Peat-derived HA are the most aliphatic, hydrophilic and enriched with amino acids and carbohydrates. Using absorption and fluorescence spectra one can discriminate organic matter source for HP from lignite, peat and lignosulphonate. Bioassays showed that HP could provide both stimulationg and inhibiting effect, depending on sensitivity of test-culture, experimental design, nature and properties of HP. In laboratory tests most of analyzed HP promoted development of roots and shoots, stimulated fluorescence of algae and affected activity of some soil enzymes at 10-100 mg/L. In field trials, preplant seed treatment with HP affected plant resistance to chemical products. In heavy metal contaminated soils application of HP decreased the toxic effects of Cu, Pb and Cd on plants. Integrated “environmental quality indicators” showed that HP at rates 0.0025 and 0.01% are able to reduce ecological toxicity in urban soils