Evaluation of metals bioavailability in agricultural soil treated with wood ash

In the present work, we aimed to study the effect of quantitative changes of micronutrients (Cu, Zn, Mn) in soil and plants caused by wood ash applied into the soil in increasing doses. A pot experiment with medium textured soil, white mustard as a test plant and six amendment treatments (doses of wood ash: 0, 1, 5, 10, 20, 30 Mg·ha⁻¹) was performed. Total contents of Cu, Zn and Mn were determined in soil and plant samples. Single (DTPA and HCl) and sequential (BCR) extractions were used to evaluate the available amounts of metals and their distribution in fractions. A plant’s ability to accumulate metals from soils was estimated using the bioconcentration factor (BCF), which is defined as the ratio of metal concentration in the plants to that in soil. The increasing doses of wood ash increased total and available contents of trace elements, especially Cu and Mn. The distribution of metals among particular fractions depended mainly on their geochemical character. The highest content of Cu was found in the reducible and oxidisable fractions, whereas, the greatest amounts of Zn and Mn were in the exchangeable and reducible fractions, and the lowest in the oxidisable fraction. Despite small wood ash influence on metal distribution in the individual soil fractions, increasing doses of wood ash increased the amounts of Cu, Zn, Mn in easily soluble fractions, which are potentially available to plants. As a result of wood ash increasing doses application, the higher amounts of Cu, Zn and Mn in plant tissues were found. However, only in the case of Zn, the value of BCF indicated on such accumulation in the plants.