The Influence of Biochar and Solid Digestate on Rose-Scented Geranium (Pelargonium graveolens L’Hér.) Productivity and Essential Oil Quality

In recent years, biochar has generated global interest in the areas of sustainable agriculture and climate adaptation. The main positive effects of biochar were observed to be the most remarkable when nutrient-rich feedstock was used as the initial pyrolysis material (i.e., anaerobic digestate). In this study, the influence of solid anaerobic digestate and biochar that was produced by the slow pyrolysis of solid digestate was evaluated by comparing the differences in the crop growth performances of Pelargonium graveolens. The experiment was conducted in a greenhouse while using three different growth media (i.e., solid digestate, biochar, and vermiculite). The results indicated that: (i) the pyrolysis of solid digestate caused a reduction in the bulk density (−52%) and an increase in the pH (+16%) and electrical conductivity (+9.5%) in the derived biochar; (ii) the best crop performances (number of leaves, number of total branches, and plant dry weight) were found using biochar, particularly for plant dry weight (+11.4%) and essential oil content (+9.4%); (iii) the essential oil quality was slightly affected by the growth media; however, the main chemical components were found within the acceptable range that was set by international standard trade; and, iv) biochar induced the presence of leaf chlorosis in Pelargonium graveolens.