Biochar and vermicompost improve growth and physiological traits of eggplant (Solanum melongena L.) under deficit irrigation

Background Drought is one of the most important environmental stresses that can adversely influence soil properties, plant growth, and productivity of agricultural crops including eggplant as an important vegetable crop. In recent years, the use of agricultural wastes has been reported as a beneficial and sustainable measure in soil water retention and fertility enhancement. In this study, the effect of date palm and pistachio biochar, vermicompost and a combination of biochar and vermicompost was evaluated on eggplant growth, yield and water use efficiency under deficit irrigation. Materials and methods The experiment was done in a split-split plot based on randomized complete block design with three replications and under open field conditions. The main plot was deficit irrigation in three levels of 100, 75 and 50% of plant water requirement (PWR), and the sub-plots were vermicompost in two levels of 0, 1500 g m−2, and biochar in three levels of 0, 500 g m−2 of the pistachio biochar and 500 g m−2 of the date palm biochar. Results The results showed that soil amendment with vermicompost and pistachio biochar and 100% PWR showed the best plant growth and performance. The early crop yield was highest under pistachio biochar and 50% PWR, while the total plant yield was highest under combined application of vermicompost and pistachio biochar at 100% PWR. The plant water use efficiency was maximum under mixed application of vermicompost and pistachio biochar at 50% PWR. Application of both pistachio biochar and vermicompost at 100% PWR resulted in the highest leaf concentrations of nitrogen, phosphorus, potassium, iron and manganese. The highest levels of physiologically important stress metabolites, including malondialdehyde, guaiacol peroxidase, superoxide dismutase and catalase enzymes were found in treatments without amendments or only with vermicompost and 50% PWR. Conclusion The results indicate that under normal and particularly water deficit conditions, vermicompost and biochar increased eggplant vegetative growth, yield and water use efficiency.