Regulated   Deficit Irrigation (RDI)

Will yield be affected by water stress?

Olive trees are normally cultivated under dry farming conditions but by applying small amounts of water, it is possible to increase production. However, if maximum yields are desired, greater amounts of water will be needed (Goldhamer, 1994).
Unfortunately, large amounts of water for irrigation purposes are not always available, especially in the most common growing areas of the Mediterranean basin.

In the driest environment, water stress accounted for major changes in the fruit growth pattern and fruit size, reduced fruit set and oil content on dry weight basis and enhanced fruit drop and advanced fruit ripening, but did not affect the oil accumulation pattern and oil characteristics.
However, by applying the right procedures of regulated deficit irrigation, (RDI) it is possible to attain maximum yield, while reducing the amount of water applied.

Critical periods for water stress – Phonological stages

A comprehensive description for the various phonological stages related to water regime was suggested by Beede & Goldhamer (1994).

Research work conducted in California, Spain, Italy, Israel and other locations concluded that the most appropriate timing for applying water stress would be through the period of massive pit hardening.

Fruit development growth stages and irrigation

Stage 1- Cell division and some cell enlargement
Stage 2 - Pit hardening
Stage 3 - Cell enlargement
The effect of RDI in the pit hardening period (stage 2 of fruit development) seems to be a useful strategy for applying regulated stress if required. RDI should be used as an irrigation strategy when there is a shortage of water. Applying a higher amount of water in the pit-hardening period will not reduce oil quality.
In experiments conducted by Prof. R. Gucci from Pisa University (personal communication), it appears that applying mild water stress could improve the process of oil extraction and also possibly influence oil characteristics. There are very interesting results which could explain new aspects of the water-plant relationship in the olive plant.