###### Abstract  
Ashes from biomass combustion (BAs) are a valuable source of plant nutrients, making them suitable for fertilizing crops. BAs also contain components that directly affect soil environmental conditions, leading to improved growth and development of plants. Their deacidifying properties allow BAs to serve as a substitute for calcium fertilizers. However, they contain substantial amounts of components that can increase soil salinity, which can have negative effects. The aim of this study was to assess the impact of BAs on changes in pH and salinity of haplichuvisol soil under the cultivation of various plant species. The study also analyzed the effects of BAs on the content of total forms of calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) in the soil. The BAs used in the experiment were sourced from a combined heat and power plant that combusts forest and agricultural biomass. These BAs are distributed as a product for fertilizing agricultural land. However, their application is not subjected to further monitoring. The results indicated that the application of different doses of BAs significantly affected the pH of the analyzed soil. Compared to control objects, a significant increase in pH was observed, with these changes dependent on the species of the cultivated plant. Additionally, even the smallest doses of BAs caused an increase in the electrolytic conductivity (EC) of soil solutions, which serves as a measure of soil salinity. Despite the increase in the average EC value, the application of BAs did not alter the salinity class. The use of BAs also significantly influenced other analyzed parameters. An increase in the average content of total forms of Ca, Mg, K, and Na in the soil was observed, along with a higher degree of soil saturation with alkaline cations, compared to the control and the soil condition before the experiment. The changes in the analyzed soil parameters were significantly influenced not only by the different doses of BAs but also by the species of the cultivated plant. The greatest fluctuations in the obtained values were observed in soil under winter rape cultivation, while the smallest fluctuations were noted in soil under spring barley and potato cultivation. s 2024 14 9812 2  
Union. In 2023, lawmakers increased the EU target for the share of renewable energy in gross energy consumption from 32% to 42.5% by 2030, aiming to reach 45% [2]. Biomass is currently the most commonly used alternative to fossil fuels for heat and energy production. Biomass is considered a carbon-neutral fuel, which can help reduce greenhouse gas emissions. However, the combustion of biomass generates large quantities of ash, currently estimated at about 50 Mt/year in Europe [3]. According to the available data, most of the ash produced during energy generation in Europe ends up in landfills [4; 5]. However, given its properties, this waste can be repurposed for other uses, including fertilizing agricultural crops [1]. The reutilization of biomass ashes (BAs) in agriculture is an important issue for creating nutrient cycles and reducing the need for chemical fertilizers [6; 7]. Data suggest that applying BAs to soil improves its properties, particularly by increasing the content of plant nutrients, reducing acidity, and enhancing structure, water retention, and microbiological activity, among others [8; 9; 10; 11; 12]. With the exception of nitrogen, BAs contain large amounts of essential plant nutrients necessary for proper growth and development [6]. The application of ash can stimulate microbial activity and mineralization processes in the soil by improving its chemical and physical properties [13]. Therefore, BAs have high potential for reuse, aligning with the EU's circular waste management policy [4]. Ashes from biomass combustion have varied effects on soil. In general, they positively influence the reduction in soil acidity, increase the degree of saturation of the sorption complex with bases, and enhance the availability of plant nutrients [9; 10; 13; 14; 15].