Unknown (2026) Enhancing Olive Yield and Oil Quality under Semi-Arid Conditions through Regulated Deficit Irrigation (RDI) in the ‘Nabali Mohassan’ Cultivar

Identification

• Journal: International Journal of Agriculture and Biosciences
• Year: 2026
• Date: 2026-01-17
• Authors: Unknown
• DOI: 10.47278/journal.ijab/2026.025

Research Groups

• Desertification Control, Environment and Climate Change, University of Carthage, Tunisia
• Agribusiness and Rural Agricultural Development Economics, University of Carthage, Tunisia

Short Summary

This study demonstrated that Regulated Deficit Irrigation (RDI) at 35% of crop evapotranspiration (ETc) significantly enhances olive yield and oil quality while saving 65–70% of irrigation water for the 'Nabali Mohassan' cultivar in semi-arid Palestinian conditions.

Objective

• To assess how regulated deficit irrigation at very low levels (15%-35% ETc) affects vegetative growth and yield of olive trees in semi-arid Palestinian climates.
• To determine the extent to which these irrigation practices affect olive oil quality, specifically free acidity, peroxide value, and total phenolic content.
• To test if regulated deficit irrigation is a viable, sustainable, and climate-resilient strategy in water-scarce environments without sacrificing agricultural production.

Study Configuration

• Spatial Scale: Field experiments conducted in established olive farms in Hebron (31.532° N, 35.099° E; 930 m above sea level) and Bethlehem (31.704° N, 35.201° E; 780 m above sea level) in Palestine, representing semi-arid Mediterranean agroecosystems. Trees were spaced at 7 meters × 7 meters (204 trees per hectare).
• Temporal Scale: Three consecutive growing seasons (2021–2024).

Methodology and Data

• Models used:
  • Reference evapotranspiration (ET₀) calculated using the Hargreaves and Samani (1985) method.
  • Crop evapotranspiration (ETc) derived as ET₀ × Kc.
  • FAO-56 Penman–Monteith method used for long-term reference evapotranspiration normals.
• Data sources:
  • Experimental Design: Complete randomized block design with five irrigation treatments: rainfed control (0% ETc), deficit irrigation 1 (DI1 = 2.5% ETc), deficit irrigation 2 (DI2 = 5% ETc), regulated deficit irrigation 1 (RDI1 = 15% ETc), and regulated deficit irrigation 2 (RDI2 = 35% ETc). Each treatment had three replicates with ten trees per replicate (total 150 trees).
  • Irrigation: Drip irrigation system (2 emitters per tree, 4 liters per hour per emitter). Reclaimed treated wastewater was applied in RDI2 plots at Bethlehem.
  • Climate Data: Long-term (2014–2023) climate normals from the Palestinian Meteorological Department.
  • Soil Data: Surface soil (0–30 cm) characterized for texture (loam to sandy-loam), bulk density (1.42 grams per cubic centimeter), field capacity (24% v/v), and wilting point (12%).
  • Vegetative Growth: Shoot length (centimeters), canopy density (%), and trunk diameter growth (centimeters) measured at the end of each season (October).
  • Olive Yield: Total fresh fruit mass (kilograms per tree) measured at harvest.
  • Olive Oil Quality: Evaluated using International Olive Council (2023) protocols for free acidity (% oleic acid), peroxide value (milliequivalents of oxygen per kilogram), and total phenolic content (milligrams of gallic acid equivalent per kilogram, Folin–Ciocalteu method). Sensory attributes scored by an IOC-accredited panel.
  • Statistical Analysis: One-way ANOVA and Tukey's HSD post-hoc test (α = 0.05) using SPSS v.26.

Main Results

• Yield Enhancement: RDI2 (35% ETc) significantly increased mean olive yield by approximately 20% (26.5 ± 1.8 kilograms per tree) compared to the rainfed control (22.0 ± 1.6 kilograms per tree).
• Water Savings: RDI2 saved approximately 65–70% of seasonal irrigation water compared to estimated full irrigation (100% ETc, approximately 43,500 liters per tree in Hebron and 38,500 liters per tree in Bethlehem).
• Improved Oil Quality: RDI2 oils exhibited the highest total phenolic content (32.0 ± 1.5 milligrams GAE per kilogram), lowest free acidity (0.40 ± 0.01%), and lowest peroxide value (12.0 ± 0.7 milliequivalents of oxygen per kilogram).
• Vegetative Growth: RDI2 showed the highest mean shoot length (38.0 ± 1.5 centimeters), canopy density (78.0 ± 1.5%), and trunk diameter growth (1.70 ± 0.07 centimeters), significantly outperforming the rainfed control.
• Reclaimed Water Integration: The use of reclaimed treated wastewater in RDI2 plots maintained soil moisture during critical reproductive periods without negative impacts on plant performance or oil quality.

Contributions

• This study establishes the lower operational threshold of Regulated Deficit Irrigation (RDI) for olive trees, demonstrating the agronomic feasibility of irrigation below 40% ETc (specifically 15-35% ETc) in semi-arid conditions.
• It provides one of the first multi-season trials confirming the possibility of such extreme water cuts while maintaining or enhancing olive yield and oil quality.
• The research innovatively incorporates treated wastewater into the RDI regime, promoting circular water use and offering a climate-resilient irrigation strategy for water-scarce regions like Palestine.
• It offers a scientific foundation for developing scalable RDI protocols, farmer education, and national adaptation plans, contributing to Sustainable Development Goals (SDGs) 6 (Clean Water and Sanitation), 12 (Responsible Consumption and Production), and 13 (Climate Action).
• The findings are highly relevant for climate adaptation models across the Eastern Mediterranean region and other water-scarce areas globally.

Funding

This study received no financial support from any organization or agency.

Citation

@article{Unknown2026Enhancing,
  author = {},
  title = {Enhancing Olive Yield and Oil Quality under Semi-Arid Conditions through Regulated Deficit Irrigation (RDI) in the ‘Nabali Mohassan’ Cultivar},
  journal = {International Journal of Agriculture and Biosciences},
  year = {2026},
  doi = {10.47278/journal.ijab/2026.025},
  url = {https://doi.org/10.47278/journal.ijab/2026.025}
}