Complementary irrigation for sustainable production in olive groves in Palestine

•We investigate olive tree responses to complementary water irrigation in Palestine.•We identify minimum irrigation levels to induce significant increases of production.•35% of total estimated water requirement helps to increase fruit production per tree.•Oil production per tree doubled when 35% of total water requirement was applied.•Tested water irrigation regimes did not affect the vegetative growth of the shoots. Prolonged drought stress in Palestine is one of the major limiting factors in the production and yield of the fruit of the olive tree, as this directly affects crop load, oil production per tree, oil quality and alternate bearing. The objective of the present study was to investigate the use of limited amounts of water as complementary irrigation to improve olive fruit growth and yield at harvest. Field-grown adult olive trees (Olea europaea L. cv. Nabali Baladi) were selected in three villages on the northern West Bank, and they were subjected to different complementary irrigation regimes from June to September, 2010. They were thus supplied with 1, 3, 6m3 water irrigation per tree over this entire period, corresponding to 2.4%, 7.1%, 14.2% of the whole seasonal water requirement per tree (42m3 water), respectively. Additional five rain-fed trees per site were used as controls. In one of the three villages, an additional treatment with 15m3 (35.6% of the total need) water irrigation per tree, was also applied. The results showed that the fruit size, pulp-to-pit ratio (on a fresh and dry weight basis) and 1-year-old mixed shoots were not affected by these water irrigation regimes. Total fruit yield per tree increased as the water irrigation increased, with the greatest effects for the highest water irrigation treatment, due to a higher number of fruits per tree (apparently due to lower fruit abscission). This study demonstrates that complementary water irrigation of olive trees to 35% of the whole seasonal water requirement can produce positive effects on olive fruit production in Palestine.