Valorization of sorghum ash with digestate and biopreparations in the development biomass of plants in a closed production system of energy

Replacing chemical fertilizers with non-toxic waste that meet all fertilizing purposes, including ash from plant biomass and their management is becoming the important goal of sustainable agriculture concerning energy plants production in a closed system. This study aims to explore a novel strategy for utilizing natural sorghum ash together with digestate and ecological compounds, to replace synthetic fertilizers, for the energy plant development improvement and thus reduction of the environment pollution. Sorghum, as an energy plant, cultivated in low quality sandy and podzolic soils, in Central and North Poland climate, was fertilized with different doses of YaraMila Complex, a synthetic fertilizer (0, 150, 300 kg ha(−1) Each dose was supplemented with different amounts of sorghum ash (0.5, 1, 2 and 4 t ha(−1)), used alone or with addition of APOL-HUMUS (soil improver; 10 L ha(−1)), biogas plant digestate (30 m(3) ha(−1)) and Stymjod (nano-organic leaf fertilizer; 5 L ha(−1)). Added to each YaraMila Complex dose, the applied ash amounts (optimally 2–4 t ha(−1)), increased growth of plants, crop biomass, index of chlorophyll content, net photosynthesis, transpiration, stomatal conductance, content of intercellular CO(2), activity of acid and alkaline phosphatase, RNase and dehydrogenase and energy properties. Sorghum ash used with the lesser YaraMila Complex doses of 0 or 150 kg ha(−1) caused the enhanced growth of plants more than the doubled YaraMila Complex amounts applied alone (150 or 300 kg ha(−1), correspondingly). Additionally, applied biogas plant digestate, APOL-HUMUS and Stymjod further increased the plant growth. This indicates that the application of natural sorghum ash accelerates energy plant development, can reduce by half the recommended synthetic fertilizer doses on poor and marginal soil and enables the cultivation of sorghum in a closed production cycle.