THE EFFECT OF ORGANIC AMENDMENTS ON SOIL CHEMICAL CHARACTERISTICS

K. I. Ivanov, V. I. Akova, N. S. Artinova, V. R. Angelova

Abstract: Enrichment of soils with organic matter could reduce the content of bioavailable metal species as a result of complexation of free ions of heavy metals. In this experiment, the influences of different rate of organic amendments on the soil chemical characteristics, as well as organic content and humus fractions and their ability to reduce heavy metal availability in contaminated soils were investigated. The field experiment was conducted on soils contaminated by the Non-Ferrous-Metal Works near Plovdiv, Bulgaria. Different amounts of vermicompost and compost (5 and 10 g.kg-1) were incorporated into the top 20 cm of soil. To determine the effect of the organic amendments, the soil samples were collected 1 month after addition of organic amendments from depth of 20 cm. The soil characteristics (pH, EC, organic content and humus fractions) were determined. The total content of micro, macroelements, heavy metals and concentration of their available species in the soil were determined using aqua regia and DTPA extraction, respectively. The results showed that compost and vermicompost treatments had significant effect on soil physical and chemical properties like EC, pH, organic matter, macro and micronutrients content. Compared with the unamended soil, soil treated with organic amendments showed apparent increases of organic matter, total N, pH, EC and available macroelements (P, K, Ca and Mg). Organic amendments influenced considerably the humus fractions by changing the ratio CHA/CFA in favour of the humic acids, in which changes of the type of humus from filvic type in control to humic-fulvic type in addition of 5 g.kg-1 and 10 g.kg-1 vermicompost and humic type in addition of 10 g.kg-1 compost. Application of the compost and vermicompost reduces the amount of aggressive fulvic acids, organic matter components that pose a potential environmental risk. The results of the present study indicated that soil application of compost and vermicompost decreased DTPA-extractable levels of heavy metals in the soil. This is indicative of heavy metals immobilisation by humic substances from compost and vermicompost application. Results appear that verify the function of humic acid in improving phytoremediation efficiency of soils contaminated with heavy metals and potential environmental availability of metals may be controlled by soil organic amendments.

Keywords: availability; contaminated soils; heavy metals; micro and macroelements; organic amendments; organic carbon

Date published: 2019-01-28