Evapotranspiration-Regulated Irrigation Scheduling in Olive Using Recycled Water
Annual Report Submitted to MERIMIS

Arnon Dag. Department of Fruit Tree Sciences, Institute of Horticulture, Agricultural Research Organization, Gilat Research Center.
Alon Ben-Gal. Department of Environmental Physics and Irrigation, Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, Gilat Research Center.
Fathi Abed El Ahadi. Olive specialist. Extension Service. Ministry of Agriculutre, Israel.

Abstract
Olives are traditionally not irrigated and recent large-scale introduction of irrigation into orchards has highlighted the lack of information regarding response of olives to water, particularly concerning olive oil quality. The objectives of this project are a) to determine the effect of recycled water quantity on yield and on oil quality, b) to evaluate methods for determination of soil and plant water status in olive orchards, c) to provide olive growers with tools for optimization of irrigation regimes such that maximum yields and oil quality are achieved with minimum water use. The objective of the experiment during the period of this report was to establish a field experiment for evaluating irrigation in a commercial orchard using recycled wastewater. An experimental site was chosen in the orchards of “Tzabar Kama” adjacent to Kfar Menachem and Revadim in Israel. Sub-plots were chosen and 2 “sampling trees” labeled. Initial sampling of leaves and soil was undertaken. Irrigation treatments will begin in April of 2006. The experiment will evaluate five irrigation levels (30, 50, 75, 100, and 125% return of potential evapotranspiration in two varieties (“Souri” amd “Barnea”). Parameters to be studied include soil moisture, leaf water potential, vegetative growth rate (branch expansion), tree growth rate (trunk circumference), flowering intensity, fruit growth, fruit yield, oil content and oil quality including chemical and organoleptic characteristics.

Introduction
Olive production is historically important throughout the Mediterranean region. Traditionally, olives are not irrigated, but recently irrigation has been recognized as constructive in order a) to increase yields and quality of olives in regions with traditional olive production, b) to allow high-density olive orchards and c) to expand olive production into regions where there is not enough rainfall to otherwise support the crop. However, fresh water in the Mediterranean region is scarce and only low-quality sources of water are available for olive irrigation. Olives are a natural candidate for utilization of low quality and recycled water as they are generally considered moderately tolerant to salinity and highly tolerant to boron.

Research Objectives
1) To demonstrate the potential of recycled water for olive irrigation.
2) To evaluate water requirements for olives in Israel and the region.
3) To determine effects of deficit irrigation on growth and production of olives.
4) To develop irrigation regimes for efficient water management of olives based on potential evapotranspiration measurements and development of appropriate crop factors.
5) To analyze monitoring methodology for water status and stress of irrigated olives.

Stategies, Procedures and Methodologies
Meteorological data (wind speed; radiation; temperature (air and soil); relative humidity; rain) collected at the site will be used to compare methods of calculating ETp (modified “Penman-Montheith” type ETp calculations and “Class A” pan measurements). Water application quantities measured as percent return of ETp will be compared in order to quantify effect of irrigation water quantity on growth of olive trees and on yield and quality of oil produced. The research is conducted in a 20 dunam (2 hectare) section of a four year old commercial olive orchard (Tzabar Kama) with general upkeep and horticultural practices in accordance with accepted commercial practice. The orchard is located adjacent to Kfar Menachem and Revadim in Israel. The section includes both “Souri” and “Barnea” varieties where between every four rows of Barnea there are two rows of Souri. The orchard is drip-irrigated with local reclaimed wastewater. Irrigation return rates equivalent to 30, 50, 75, 100 and 125% of ETp (% rate X ETp X cover factor) are compared. The cover factor is % surface cover by trees in the orchard and will be determined by measuring shaded area at solar noon. Treatments are given to blocks of 24 trees (6 rows X 4 trees). The statistical design is randomized complete-block with 4 - 5 replicates per treatment. Each of the 26 experimental units will consist of six adjacent tree rows (4 Barnea and 2 Souri) with at least 4 olive trees per row. Two central trees of each variety are monitored while those surrounding will serve as border-guard trees.
Initial description and categorization of the soils in the orchard is being completed through determination of basic chemical and physical properties using standard methods. Analysis includes organic matter content and hydraulic properties including hydraulic conductivity and water retention. Soil water potential will be monitored for each treatment at three depths (30, 60 and 90 cm), below irrigation water emitters using tensiometers. Plant water status will be assessed by predawn leaf water potential using Scholander-type pressure chamber. Content of specific elements will be determined in representative tree from each treatment in winter and summer sampling. Seasonal shoot growth will be evaluated in 4 young shoots in each of the monitored trees (two per replicate) by measuring a labeled shoot each year during April and September. Each orchard and each treatment will be harvested according to its appropriate ripening stage. Yield will be determined for each monitored tree. Oil percentage will be measured in each replicate by chemical extraction. A sample of oil will be extracted from each replicate in a mill suitable for small quantities and will undergo both chemical and organoleptic analysis. Quality of the virgin olive oil will be determined as defined by the regulations and standards of both the international olive oil council and the EU. Chemical quality parameters to be tested include: FFA (free fatty acids) and their composition; peroxide value; and UV absorbance. Total polyphenols will be measured in order to determine oil stability. Organoleptic quality testing will be conducted to determine both positive and negative aesthetic attributes.

Results – 2005
1. Acquirement of funding necessary to establish experiment
2. Detection and procurement of specific experimental site
3. Choice and labeling of sub-units for treatments and replicates
4. Choice and labeling of “sampling trees” in each sub-unit
5. Initial (pre treatment) soil and leaf sampling
6. Design, ordering, placement and employment of experimental irrigation system
7. Launch of irrigation treatments April 2006.

Discussion
Results of the experiment as it advances will allow development of water saving and yield maximization in closely-spaced olive orchards in dry areas and will allow greater understanding of irrigation-water demand-yield-oil quality in olives. It will also demonstrate the feasibility of recycled water for olive irrigation. The data collected, including meteorological data, will be used for decision making and optimization of available irrigation water and for the potential for deficit irrigation regimes in olive cultivation.