THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF THE DATE PALM (Phoenix dactylifera L.): A REVIEW

Date palm is a crop suited to hot, arid regions. It originated in Mesopotamia and the centres of production are in West Asia and North Africa. Despite its regional and international importance, and its dependence on irrigation or a shallow water table for survival, relatively little research has been published on the water relations and irrigation need of date palm. Following early work in California, the majority of the recent research reported in the literature has been conducted in Saudi Arabia and Tunisia. The date palm has a terminal crown of 100-120 leaves. At the base of each leaf is an axillary bud, most of which develop in the winter as flower buds. It takes 150-200 days from pollination to fruit maturity Stomata occur on both leaf surfaces. Different techniques have been used to measure the water use of date palm, including micrometeorological and sap flow methods. In Syria, mean actual evapotranspiration rates varied between 0.5 mm d(-1) (winter) and 3.5 mm d(-1) (summer), in Saudi Arabia from 2-3 to 8-11 mm d(-1) depending on location and in Jordan from 2 to 8-10 mm d(-1) respectively. In Tunisia, there was some (limited) evidence of stomatal control of transpiration rates (seasonal range 0.5 to 3.5 mm d(-1)) when temperatures exceeded 32 degrees C. Experimentally determined values of the crop coefficient were inconsistent, varying from 0.6-0.7 to 1.18. In the vicinity of an oasis, advection may increase potential water use substantially above that of a reference crop. In the absence of a shallow water table, roots can extract water from soil depths greater than 2 m. There is little published information on the water productivity of date palm. A target benchmark figure is probably about 1.3-kg fresh fruit m(-3) of irrigation water applied. Under controlled conditions, phenotypes differed in their responses to water stress. The date palm is traditionally considered to be relatively salt-tolerant, with a threshold electrical conductivity value for the saturated soil extract of 4.0 dS m(-1), but recent evidence from Israel suggests that this view may be mistaken. Since early times, flood irrigation has been used to irrigate date palm and it is still probably the most common method in many countries. Since the 1980s, farmers have been encouraged by governments to use localised irrigation methods (e.g. micro-sprinklers, drip and bubbler) as a means of saving water. Since water is a scarce resource in the West Asia and North Africa region, research should focus on developing ways to improve the water productivity of this high value crop.