Effects of Palm Leaf Biochar on the Availability of Soil Nutrients, Leaf Nutrient Concentration, and Physiological Characteristics of Melon Plants (Cucumis melo L.) Under Drought Stress

To investigate the effect of palm leaf biochar on the element absorption and reduction of drought stress effects in melon plants, an experiment was conducted using a split plot in a randomized complete block design with three replications in two successive years. The main plot contained three levels of drought stress (60%, 85%, and 100% water requirement) and the subplot contained four levels of biochar (0, 150, 300, and 450 g per plant). The results revealed that biochar application reduced the effect of drought stress and thus proline content in plants. Application of 300 g biochar per plant with 100% water requirement increased total chlorophyll by 131% compared to control. The treatment of 450 g biochar per plant with 100% water requirement increased chlorophyll a and b and leaf nitrogen (N), potassium (K), calcium (Ca), and manganese (Mn) content by 169%, 127%, 58%, 65%, 44%, and 48%, respectively, compared to control. The treatment of 450 g biochar per plant increased phosphorus (P) and magnesium (Mg) content of leaves by 20% and 31%, respectively, in comparison with control The interaction of drought stress and biochar indicated that the treatment of 450 g biochar per plant with 60% of water requirement increased plant iron, zinc, and copper by 60%, 44%, and 66%, respectively, compared to the biochar-free treatment with 100% water requirement. Addition of 450 g biochar per plant and irrigation with 60% of water requirement increased soil N, P, and K by 150%, 13%, and 75%, respectively, compared to the biochar-free treatment with 100% water requirement. The results indicated that the use of biochar can be a successful strategy for improving water use efficiency and reducing drought stress in melon plants.