Effects of different levels of humic acid on growth indices and essential oil of lemon balm (Melissaofficinalis L.) under different irrigation regimes

Due to increased environmental issues, more attention has been paid to biofertilizers. This experiment was conducted as factorial with completely randomized design with three replications. Treatments included irrigation at 100 (control), 75 and 50% FC and humic acid spraying at 0, 200 and 400 mg l-1. The most and the least plant height, fresh and dry weight, number of lateral branches, stem diameter and root dry weight were observed for irrigation at 100% FC and 50% FC, respectively. Whilst, the highest essential oil percentage and essential oil yield was achieved for irrigation at 50% FC and 75% FC, respectively. Interaction of 400 mgl-1 humic acid and irrigation at 100% FC had the most plant height, fresh and dry weight, stem diameter, and root dry weight. Meanwhile, application of 400 mg humic acid and irrigation at 50% FC and 75% FC had the highest essential oil percentage and essential oil yield, respectively. The interaction was not significant for number of lateral branches. Vegetative growth decreased with increasing drought stress and increased with increasing humic acid application. These results suggested that humic acid alleviated drought stress on lemon balm.