2.3. Growth experiment
The experiment was carried out on two soil types: loamy sand (LS) and clay (C) collected from the 0-0.2 m layer in southern Poland. The properties of the soils used in the experiment are presented in Table 2.
The growth experiment was conducted in containers with a capacity of 500 g of soil dry mass. The experimental scheme was the same for LS and C soils and included the following treatments: the control with no cavitated charcoal (LS-0; C-0), a treatment with a 1.76% addition of cavitated charcoal (LS-1; C-1), a treatment with a 3.5% addition of cavitated charcoal (LS-2; C-2), a treatment with a 7.0% addition of cavitated charcoal (LS-3; C-3), and a treatment with a 14.0% addition of cavitated charcoal (LS-4; C-4). After introducing cavitated charcoal, distilled water (up to 45% water capacity) was added to the soils and thoroughly mixed with the material. Subsequently, soils with and without the addition of charcoal were placed in PVC containers. After 24 hours, seeds of Sorghum saccharatum SOS 101116 were sown. During plant growth, the soil moisture content was maintained at 60% of the water capacity. The experiment was carried out under laboratory conditions at 25±3 °C for 156 days. Then, plant aboveground biomass was collected, and plant roots were separated from the soil block and thoroughly washed with distilled water. The collected biomass was dried to a constant weight at 105 °C, and then, the amount of biomass was determined. To determine the chemical composition, the plant material was ashed in a chamber furnace at 450 °C for 12 hours, and the residue was dissolved in diluted (1:2) (v/v) nitric acid. The contents of the studied trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES, Perkin Elmer Optima 7300 DV, Waltham, USA) (Oleszczuk et al., 2007).