The effect of humic acid application on drought tolerance of miscantus (Miscanthus × giganteus)

Drought is one of the most important environmental factors limiting plant growth, development and plant production. This study was conducted to determine drought tolerance of the effects of humic acids under different irrigation levels ([100% irrigation (S0-control), 75% irrigation (S1), 50% irrigation (S2), 25% irrigation (S3), 0% irrigation (S4)]) in miscanthus (Miscanthus x giganteus). It was carried out in plastic pots under greenhouse conditions during the 58 days in 2019, according to the randomized plot design with three replications. In the study, different irrigation levels had a negative effect on plant growth at varying rates, and a decrease was observed between 3% and 86% rates when compared to control plants in terms of plant growth parameters (plant height, stem thickness, leaf width, number, and area of leaves, leaf, and stem, root fresh and dry weights). Additionally, humic acid treatments improved plants' resistance to drought stress, and the reduction in growth parameters when compared to control plants stayed between 7% and 45%, while an average improvement of between 8% and 34% was obtained when compared to plants without HA. When compared to control plants, different irrigation amounts had a comparable impact on physiological markers (LRWC, LWP, MII, and Chlorophyll) and reduced between 1% and 278%. Humic acid treatments also showed a beneficial impact on physiological indicators, with an average decrease of 9-61% compared to control plants and an average improvement of 11-33% compared to plants without HA. According to the study, humic acid is helpful in promoting drought tolerance in miscanthus and in alleviating the impacts of stress.