3.2. Effect of the addition of cavitated charcoal on selected chemical properties of soils
The application of CHAR-C reduced the acidification of the LS and C soil (Table 3). Due to the greater buffering of the C soil than of the LS soil, the efficiency of the deacidification effect of CHAR-C was lower. According to the literature, the application of charcoal in soil reduces soil acidification as a result of active compounds and alkaline elements accumulated in this material. The durability of the charcoal deacidifying effect depends on soil and climatic conditions and, as indicated by the published data, on the rate of alkaline cation leaching to the deeper layers of the soil profile (Hardy et al., 2016; Mastrolonardo et al., 2019).
An increase in the electrical conductivity (EC) value was noted in proportion to the amount of CHAR-C introduced into the LS soil; however, the parameter increase was significant only in the LS-4 treatment with the highest CHAR-C rate (Table 3). Introduction of the 7.0% (C-3) and 14.0% (C-4) rates of CHAR-C into the C soil significantly increased the EC values by 80% and 109%, respectively, compared to in the control soil (C-0). Due to the lack of data in the literature on the effect of cavitated charcoal on soil EC values, the obtained results were referenced in terms of the effect of applied biochar to the soil on the parameter value. The literature provides examples of increases in EC values after the application of biochar. The EC increase was generally proportional to the rate of the material used. This phenomenon results from the release of salts from organic connections that easily pass into the soil solution, increasing the pool of ionic forms that actively conduct an electrical charge (Gondek and Mierzwa-Hersztek, 2016).
Significant differences in the total carbon (CTot) content in the soils were found after using the same rates of CHAR-C (Table 3). Considering only the smallest rate of CHAR-C introduced into the LS soil, an over 40% increase in the CTot content was noted, while this content in the C soil decreased by over 8% compared to that in the control. The highest rate of CHAR-C resulted in a 197% increase in the CTot content in LS and a 19% increase in C compared to that in the control treatments. The trend in the increased CTot in this study is confirmed by the literature on the charcoal effect on the carbon content in soil (Hardy and Dufey, 2017; Mastrolonardo et al., 2019). However, it should be noted that there are large discrepancies in the values of the increased CTot content in soils, which are probably dictated by the type of charcoal used, its rate, and climatic conditions (Kerré et al., 2016).
The total nitrogen content differed significantly but only between soils (Table 3). No significant changes in the total nitrogen (NTot) content were noted after the application of CHAR-C. The literature lacks information on the effect of the tested product on the N content in soil. Hardy et al. (2016) did not report significant differences in the nitrogen content between the soil fertilised with charcoal and the control soil. Hirsch et al. (2017) discovered even lower N content in soils into which charcoal was introduced. However, it should be noted that charcoal contains a nitrogen pool in a heterocyclic form that is practically inaccessible to plants, creating the need to include fertilisation with mineral forms of this element.