Fertilisation Potential of Combined Use of Wood Biomass Ash and Digestate in Maize Cultivation

In recent years, there has been growing interest in using wood biomass for energy production, which has led to an increase in post-processing waste in the form of wood biomass ash (WBA). Due to the rich composition of WBA, its fertilising potential should be considered. In the conducted studies, WBA was used both alone and in combination with digestate (DG). The WBA was obtained from the Municipal Heat Energy Company and the DG from the Agricultural Biogas Plant in the form of unseparated liquid digestate (ULD), separated solid digestate (SSD) and separated liquid digestate (SLD). The studies included four series: (1) WBA, (2) WBA + ULD, (3) WBA + SSD and (4) WBA + SLD. In each series, WBA was introduced in three increasing doses (0.5, 1.0 and 1.5, expressed in hydrolytic acidity units (HACs) and determined based on the general alkalinity of the material). The digestates (DGs) were applied in fixed doses, which were balanced with respect to the nitrogen introduced into the soil. The test plant was the maize (Zea mays L.) variety Garantio, which was grown in a vegetation hall. The obtained results indicate that the combined use of WBA and DGs (especially ULD and SLD) had a positive effect on the plant height, leaf greenness index (SPAD), and thus, maize yield and dry matter content. In the series with DG addition, the maize yield ranged from 615.5 g (WBA + SSD) to 729.6 g pot−1 (WBA + SLD), which was 28–52% higher than in the series with WBA alone. In turn, the application of increasing doses of WBA alone did not significantly affect the biomass yield but significantly increased the content of N (34%), K (60%), Mg (56%), Ca (60%) and Na (4%). In the series with WBA and DGs, the increase in the content of the above-mentioned macronutrients depended on the type of DG and the dose of WBA. The exception among the macronutrients was P, whose content generally decreased (by 4–23%) with an increasing WBA dose, regardless of the test series. The most favourable results in terms of the chemical composition, excluding the P content, were observed following the combined application of WBA and liquid forms of DG (ULD and SLD).