Effects of Sewage Sludge Biochar as a Growing Media Component and Phosphate Fertiliser on the Cultivation of Potted Ornamental Plants

Abstract

There is increasing pressure from the German government on its citizens to reduce dependency on phosphate rock and peat, in agriculture and horticulture. This is due to the phosphate rock oligopoly with associated political instabilities, and the environmental consequences of peat harvesting. Past studies on soilless crop cultivation have shown promising outcomes for the phosphorus (P)-rich sewage sludge biochar (SSB) as an answer to these issues. However, SSB remains as one of the least studied biochar types in soilless ornamental cultivation. The objectives of this study were to investigate the viability of SSB as a P fertiliser and growing media component in pot cultivation of lavender (Lavandula angustifolia), purple coneflower (Echinacea purpurea) and poinsettia (Euphorbia pulcherrima). The addition of SSB at a 10% (v/v) rate to coco peat (SSB 10) was determined as the best composition. Although it did not outperform the control, SSB 10 plants were not significantly lower than the control plants in height, dry aboveground biomass, and number of poinsettia stems across all three species – except in poinsettia biomass. Other rates (5%, 15%, 20%) had significantly lower values in more than one parameter. Physicochemical characterisation also revealed increased P with increasing SSB rates in the growing media. Contrary to other studies, the pH of all growing media did not exceed ideal growing media pH values (5.3-6.5), further solidifying SSB’s viability as a growing media component. The reliability of our results could be improved by recording water uptake of the media, and selection of species with quantifiable aesthetics