This two-year study was focused on the effect of the application of different biomass ash doses on selected soil physical properties, i.e., soil moisture (SM), bulk density (BD), penetration resistance (PR), and soil stability in water measured by the content of readily dispersible clay (RDC), following control and mineral NPK fertilization in the cultivation of winter oilseed rape (Brassica napus L. var. napus). A one-factor field experiment conducted on podzolic soil (control, NPK, 100, 200, 300, 400, 500 kg K2O·ha-1) showed that the use of biomass combustion ash significantly improved soil moisture at all depths and variants, and especially at a depth of 30-35 cm in the 500 kg·ha-1 variant, i.e., by 2.99% v/v, compared to NPK. In turn, the moisture content in the 30-35 cm layer increased by 3.19% v/v in all variants in both years compared to the control. In 2020 and 2021, bulk density in the 0-5 cm layer treated with a dose of 500 kg·ha-1 exhibited a positive 0.15 and 0.12 Mg·m-3 decrease, respectively, compared to the control. In both years, the BD values in the 30-35 cm layer were reduced by 0.14 and 0.16 Mg·m-3 compared to the control. The PR values decreased in the treatments with doses of 300, 400, and 500 kg·ha-1, especially in 2021. The RDC content was found to decline in both years, i.e., 2020 and 2021, upon the application of even the lowest dose (100 kg·ha-1) in all the analysed layers. The reduction in the RDC content, especially in the 0-5 cm layer, is very important for soil structure stability and to protect the soil environment. This layer is most susceptible to crusting, which results in poor aeration and weak plant emergence during drought and/or periods of excessive moisture. It may also increase surface runoff and intensify soil erosion processes.
Keywords: biomass ash; penetration resistance; readily dispersible clay; soil bulk density; soil moisture.