Model of Biomass Productivity under the Influence of Change in the Phytotoxicity of Podzol Soil Due to Reintroduction of Sewage Sludge under Energy Willow

Utilization of sewage sludge during phytoremediation of territories and its introduction as fertilizer for energy crops requires testing for phytotoxicity of the soil cover, which will allow determining an ecologically safe dose of its use and minimizing the negative impact on agroecosystems. It will also contribute to the formation of optimal productivity of agrophytocenoses as well as optimize the nutrition conditions for intensive growth and development of cultivated plants. The research conducted an analysis of the impact of the increase in phytotoxicity of sod-podzolic soil from the introduction of fresh sewage sludge and its composts with various organic materials (sawdust of coniferous trees, straw of grain crops) on the formation of biomass productivity of energy willow during a repeated cycle of cultivation. Regression and correlation analyses were used to build a mathematical model of biomass productivity under the influence of changes in the phytotoxicity of podzol soil due to repeated introduction of sewage sludge under the energy willow. The obtained regression dependences show that the formation of phytotoxicity of sod-podzolic soil is most affected by the increase in the content of Pb and Cd. However, the introduction of the norm of fresh SS within 80 t/ha did not lead to an increase in the content of these heavy metals above the maximum allowable concentrations, although it contributed to an increase in phytotoxicity to an above average level. The maximum predicted productivity, depending on the content of mobile forms of heavy metals in the soil, is about 60 t/ha at a content of Cd = 0.25; Ni = 1.1 Pb = 4.6 mg/kg soil. As the phytotoxicity of the soil increases to an above-average level (phytotoxic effect 40–46%), the intensity of biomass accumulation of energy willow slows down somewhat. In general, after a repeated cycle of using the plantation during the 4-year growing season of energy willow in all options where fertilizers were applied, the productivity of wood biomass increased significantly compared to the control option by 7.7–17.4 t/ha and with the smallest significant difference between the indicators of the research options 4.23 t/ha.