High-value biochar from sunflower husk pyrolysis enhances growth and physiological performance of Spirodela polyrhiza

Rising populations intensify food demand and place increasing pressure on already degraded soils, driving the need for sustainable, waste-derived fertilizers that can enhance plant growth. This research aimed to assess the potential use of biochar as a soil amendment to support plant growth. The biochar used in this study was produced from sunflower husk and examined in three variants obtained at pyrolysis temperatures of 300, 400, and 500 °C, applied at different dosage levels. Spirodela polyrhiza served as the model plant species. Assessment was based on changes in chlorophyll index, fluorescence, frond number, and overall plant condition. Temperature-dependent changes in biochar properties were further analysed using SEM, FTIR, BET, and GC-MS. The results indicate that the pyrolysis products used in this study did not exhibit toxic effects on Spirodela polyrhiza growth. Instead, all analysed variants showed a generally positive influence on plant development, reflected in a clear stimulatory response. The findings demonstrate that the impact of biochar on plant growth was strongly dependent on both the pyrolysis temperature and the applied dose, with the most favourable outcomes observed for biochar produced at 400-500 °C. Overall, the study identifies sunflower husk as a duckweed growth-stimulating material and supports its further consideration as an environmentally safe, waste-derived fertilizer component.