Potassium humate improves physio-biochemical attributes, defense systems activities and water-use efficiencies of eggplant under partial root-zone drying

Partial root-zone drying (PRD) applied in an alternate strategy (PRDalt) can regulate plant physiological and antioxidative defense system responses, and it is considered as an irrigation water-saving method. The current study was carried out using pot experiments to elucidate the potential role of potassium humate (KH) in integration with PRDalt in regulating eggplant physiological and defense systems responses, and irrigation water-saving. PRDalt significantly reduced the plant growth and yield, leaf photosynthetic gas exchange, leaf relative water content (RWC) and membrane stability index (MSI), while significantly increased leaf and root contents of malondialdehyde (MDA), hydrogen peroxide (H2O2), and leaf and root activities of enzymatic and non-enzymatic antioxidants compared to Full irrigation (control; FI). Integrative application of PRDalt + KH increased water-use efficiencies; WUEfw (calculated as g fruits L−1 applied water) by 97.9% and WUEpt (calculated by dividing the net photosynthetic rate by transpiration rate) by 20.3% compared to the controls. It also further increased leaf and root activities of enzymatic and non-enzymatic antioxidants, while controlled the contents of MDA and H2O2, and maintained plant growth and yield, leaf photosynthetic gas exchange, RWC and MSI at the same levels in plants of FI. Results of this study recommend using the integrative strategy of PRDalt + KH to confer the same eggplant growth and yield of the FI control and save about 50% of irrigation water.