Short-Term Effect of Fly Ash from Biomass Combustion on Spring Rape Plants Growth, Nutrient, and Trace Elements Accumulation, and Soil Properties

The short-term impact of biomass combustion fly ashes (BAs) fertilization on the spring rape growth, essential and trace elements accumulation in seeds, and selected soil and soil solution properties were analyzed in a pot experiment study. The pot experiment was carried out in the growing season (April-August) during the year 2018. The effect of BAs on the dry matter content in spring rape plants and the relative content of chlorophyll in leaves (SPAD) was analyzed. In addition, the effect of BAs on the accumulation of essential and trace elements in the seeds of this plant was analyzed. The impact of BAs on the basic physicochemical properties of soils was also assessed. Additionally, the solubility of compounds contained in BAs was monitored on the basis of the analysis of the changes in the physicochemical properties of soil solution during the experiment period. The present study demonstrated a positive effect of BAs fertilization on plant growth and development and improvement of soil physicochemical properties. A change has been achieved in the soil reaction class from a slightly acidic (control, NPK) to neutral (D1-D6), with the highest increase in pH induced by the highest ash dose of 3 mg ha^-1 (D6). It was shown that BAs contributed to a significant increase in the content of macroelements than trace elements in the analyzed soil. In turn, the accumulation of these elements in plant seeds exhibited an inverse relationship, which was mainly influenced by the soil pH and the content of N, Ca, Mg, K, and Na in the soil, as indicated by the correlation coefficients. The highest contents of Fe, Mn, Zn, Cu, Cr, and Ni were detected in the seeds of plants fertilized with BAs at a dose of 2.0 Mg ha^-1 (D4), and their respective values were 263, 363, 107, 51, 1835, and 137% higher than in the control. The Ca, Mg, S, and Na compounds introduced with BAs exhibited high solubility, as evidenced by the higher concentration of Ca²⁺, Mg²⁺, Na⁺, and SO₄^2- ions in the soil solutions and the dynamic changes in pH and EC observed during the experiment. The lowest solubility after the application of BAs was exhibited by N and P. The conducted PCA analysis to a large extent explained the variability between the applied fertilization and the factors analyzed in the experiment. Despite the positive impact of ashes, attention should be paid to the potential risks associated with their use. The use of higher doses of BAs may result in excessive alkalization and salinity of soils and may enhance the accumulation of trace elements in plants. These aspects should therefore be closely monitored, especially in the case of a long-term application of these wastes, in order to avoid serious environmental problems.