Enhancing Drought Tolerance in Barley (Hordeum vulgare L.) Through the Application of Olive Pomace Compost

Drought stress, a major abiotic factor, significantly threatens global agricultural productivity and food security. This study evaluated the potential of olive pomace compost to alleviate water stress in barley (Hordeum vulgare L.). A pot experiment compared well-watered (80% FC) and drought-stressed plants (40% FC), with compost applied at recommended (40 tons/ha) and double doses (80 tons/ha). Water stress reduced growth (fresh (−28.6%) and dry biomass, (−49.9%) shoot length (−20.45%)), photosynthetic pigments (chlorophyll a (−16.9%), chlorophyll b, (−52.16%) and carotenoids (−24.67%)), and water content, while impairing water relations, as shown by lower relative water content and higher water saturation deficit and consumption. Drought-stressed plants also exhibited elevated oxidative stress, indicated by increased malondialdehyde levels (+68.42%), and a modulated antioxidant defense system, with higher DPPH inhibition (+12.30%), with total phenolic content increasing by 220.70% and FRAP and ORAC values increasing by 55.18% and 37.44%, respectively. The application of olive pomace compost effectively mitigated these adverse effects, resulting in improved growth (ranging from 30% to 66%), pigment content (especially with double dose), and water relations; a lowering of oxidative stress (−37.5%); and moderation of the antioxidant response, indicating a reduced overall stress burden. The study findings show that olive pomace compost provides a sustainable and cost-effective strategy for improving crop resilience in water-scarce regions. By using this abundant agricultural waste, farmers can enhance soil health and maintain food security in the face of climate change.