THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF OIL PALM (ELAEIS GUINEENSIS): A REVIEW

Abstract

SUMMARYThe results of research on the water relations and irrigation need of oil palm are collated and summarized in an attempt to link fundamental studies on crop physiology to drought mitigation and irrigation practices. Background information is given on the centres of origin (West Africa) and of production of oil palm (Malaysia and Indonesia), but the crop is now moving into drier regions. The effects of water stress on the development processes of the crop are summarized followed by reviews of its water relations, water use and water productivity. The majority of the recent research published in the international literature has been conducted in Malaysia and in Francophone West Africa. The unique vegetative structure of the palm (stem and leaves) together with the long interval between flower initiation and the harvesting of the mature fruit (ca. three years) means that causal links between environmental factors (especially water) and yield are difficult to establish. The majority of roots are found in the 0–0.6 m soil horizons, but roots can reach depths greater than 5 m and spread laterally up to 25 m from the trunk. The stomata are a sensitive indicator of plant water status and play an important role in controlling water loss. Stomatal conductance and photosynthesis are negatively correlated with the saturation deficit of the air. It is not easy to measure the actual water use of oil palm, the best estimates for mature palms suggesting crop evapotranspiration (ETc) rates of 4–5 mm d−1in the monsoon months (equivalent to 280–350 l palm−1d−1). For well-watered mature palms, crop coefficient (Kc) values are in the range 0.8–1.0. Although the susceptibility of oil palm to drought is well recognized, there is a limited amount of reliable data on actual yield responses to irrigation. The best estimates are 20–25 kg fresh fruit bunches ha−1mm−1(or a yield loss of about 10% for every 100 mm increase in the soil water deficit). These increases are only realized in the third and subsequent years after the introduction of irrigation and follow an increase in the number of fruit bunches as a result of an improvement in the sex ratio (female/total inflorescence production) and a reduction in the abortion of immature inflorescences. There is no agreement on the allowable depletion of the available soil water, or on the associated optimum irrigation interval. Drip irrigation has been used successfully on oil palm.