Biochar as organic fertilizer and interactive effect of compost tea alternative to mineral fertilization on geranium (Pelargonium graveolens L.)

Nowadays, organic fertilizers such as biochar and compost tea have gained a huge interest in sustainable agricultural systems. Two field experiments were conducted during the 2019 and 2020 seasons to study the effect of biochar (BC) as soil applications, compost tea (CT) as foliar applications, and their combination on the growth, yield, and essential oil composition of P. graveolens. The experimental design was a randomized complete block with three replicates. Three biochar rates (0, 5, and 10 t ha-1) and four compost tea concentrations (0, 0.1, 0.2, and 0.3 %) were assigned randomly in plots. Plants were harvested twice; i.e., on 1st May and 30th September, and the following data were recorded for each cut: plant height, leaf area index, fresh herbage yield, oil %, oil yield, and chemical constituents of essential oil. Results indicated that P. graveolens growth parameters and yield components at both cuts were significantly affected by biochar application and foliar application of compost tea, and a significant interaction of these two factors also occurred. All treatments gave significantly the best values of plant height, leaf area index, and fresh herbage yield in addition to essential oil % and oil yield, in comparison with the control treatment. Among treatments, the plants receiving biochar at 10 t ha-1 in combination with compost tea 0.1% could be the best choice. The numerical increase in the abovementioned parameters, in comparison with that of control treatment, reached 115.30, 79.59, 68.85, 66.67 and 181.42 %, in the first cut and 118.66, 80.04, 65.81, 66.67 and 176.35 % in the second cuts for the tested parameters, respectively. Therefore, this treatment was recommended to achieve the highest yield and excellent quality of essential oil under these experimental conditions. Future investigation is required to determine the optimum doses of biochar and compost tea.