Yield response of a mature olive orchard to water deficit
Summary of a paper published in the Journal of the American Society of Horticultural Science, 128:425-431, 2003
Courtesy of Netafim University
Moriana, A., Orgaz, F., Pastor, M. & Fereres, E.
IAS-CSIC and University of Cordoba, Cordoba, Spain
Olive is a traditionally rain fed crop in the Mediterranean region. Consequently, little information is available regarding response to irrigation, especially under the highly variable winter rainfall conditions of the region. The objective of the present experiment was to study the water relation and yield response under variable water supply.
The field experiment was conducted in an 18-year-old olive (Olea europaea L. cv. Picual) orchard located at the CIFA Experiment Station in Cordoba, Spain. The summer months (May to September) are normally dry. The mean rainfall during the three years of the experiment was 1043, 407, and 468 mm. Irrigation was applied five days a week by drip irrigation (4 emitters of 4 L/h per tree). The five treatments were: 1) Control – irrigation based on fully replenishing water uptake by the trees (ETo); 2) Regulated deficit irrigation – applying 75% of ETo distributed outside the 4 summer months (July – September), which stayed dry; 3) Sustained deficit irrigation – applying 75% of ETo distributed throughout the year; 4) Deficit irrigation – irrigation only during the “on” (fruit bearing) year and rain fed during the “off” (non-bearing) year; 5) Dry – rain fed every year. The average for the three experimental years of the amount of applied water for the five treatments respectively was: 566, 131, 242, 445, 0 mm, and the average ETo was: 830, 566, 616, 740, 508 mm, respectively.
Yield of fruit of all treatments increased linearly between about 5 t/ha to 11 t/ha with ETo between 480 and 680 mm and remained constant (plateau) up to 900 mm. It was sufficient to apply 82 % (mean of 580 mm) of maximum ETo (mean of 830 mm) to obtain maximum yields. The rain fed treatment resulted in the lowest yield and the control treatment in the highest yield. The treatments irrigated at 75 % ETo resulted in yields falling in between with no apparent difference between them. Thus, yields depended on the quantity of water applied regardless of whether deficit irrigation was applied uniformly throughout the irrigation season or only outside the dry summer months (no irrigation during July to September). When irrigation was applied only during the “on” yield year, yields were outside (to the right of) the linear function, showing considerable waste of irrigation water (the yield was about 60% of the maximum yield when the water applied was maximum [700 mm]). The water use efficiency was 22 kg/ha-mm at low ETo and about 9 kg/ha-mm at maximum ETo (700 to 850 mm). The concentration of oil in the fruit increased as ETo and yields decreased. The yield of oil however increased from 1.0 t/ha at ETo of 480 mm to 2.0 t/ha at ETo of 800 mm (non-linear function). Mid-day leaf water potential and stomatal conductance as well as trunk growth decreased during periods of draught or by the dry treatments reflecting the water stress imposed on the trees.
Research shows that drip irrigation is an appropriate method of irrigating olives, resulting in more than doubling of the yield over rain fed conditions when evapotranspiration was fully satisfied by irrigation and rain (680 mm).