THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF COCONUT (Cocos nucifera): A REVIEW

Abstract

SUMMARYThe results of research on the water relations and irrigation needs of coconut are collated and summarized in an attempt to link fundamental studies on crop physiology to drought mitigation and irrigation practices. Background information on the centres of origin and production of coconut and on crop development processes is followed by reviews of plant water relations, crop water use and water productivity, including drought mitigation. The majority of the recent research published in the international literature has been conducted in Brazil, Kerala (South India) and Sri Lanka, and by CIRAD (France) in association with local research organizations in a number of countries, including the Ivory Coast. 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 (44 months) mean that causal links between environmental factors (especially water) are difficult to establish. The stomata play an important role in controlling water loss, whilst the leaf water potential is a sensitive indicator of plant water status. Both stomatal conductance and leaf water potential are negatively correlated with the saturation deficit of the air. Although roots extend to depths >2 m and laterally >3 m, the density of roots is greatest in the top 0–1.0 m soil, and laterally within 1.0–1.5 m of the trunk. In general, dwarf cultivars are more susceptible to drought than tall ones. Methods of screening for drought tolerance based on physiological traits have been proposed. The best estimates of the actual water use (ETc) of mature palms indicate representative rates of about 3 mm d−1. Reported values for the crop coefficient (Kc) are variable but suggest that 0.7 is a reasonable estimate. Although the sensitivity of coconut to drought is well recognized, there is a limited amount of reliable data on actual yield responses to irrigation although annual yield increases (50%) of 20–40 nuts palm−1 (4–12 kg copra, cultivar dependent) have been reported. These are only realized in the third and subsequent years after the introduction of irrigation applied at a rate equivalent to about 2 mm d−1 (or 100 l palm−1 d−1) at intervals of up to one week. Irrigation increases female flower production and reduces premature nut fall. Basin irrigation, micro-sprinklers and drip irrigation are all suitable methods of applying water. Recommended methods of drought mitigation include the burial of husks in trenches adjacent to the plant, mulching and the application of common salt (chloride ions). An international approach to addressing the need for more information on water productivity is recommended.

FAO CROPWAT Model-Based Irrigation Requirements for Coconut to Improve Crop and Water Productivity in Kerala, India

“…Even if we take the higher part of the irrigation requirement, approximately 100 L of water per palm per day could be saved, and if the quantum is converted for the entire coconut irrigated area, it will be a saving of a huge quantity of water at a state level. Carr [1] summarized the water relations and irrigation requirements of coconut by daily water use from various studies carried out around the globe, and indicated a range of 75 to 220 L per palm per day, which is nearer to our current findings. The current recommendation of the Kerala Agricultural University is on the higher side, when compared with the output from the current study [32].…”

“…Even though coconut is found mainly in coastal areas, it can grow in various soils with different moisture conditions and regimes. In Kerala, it is mostly grown in laterite/lateritic soils of the ultisol order (gravelly soils), which are prone to drought and are frequently exposed to intermittent moisture shortfall throughout the summer season [1]. This moisture deficit during its growth stage has a serious impact on its productivity [2].…”

“…This moisture deficit during its growth stage has a serious impact on its productivity [2]. Many researchers have reported an impediment in the growth of recently planted trees, and a yield decline in mature trees because of a moisture deficit, which makes the cells of the coconut root absorption zone sedentary as a result of processes such as desiccation and suberization, thereby harmfully disturbing the water and nutrient absorption process [1,3]. Several studies suggest the prominence of irrigating coconut fields, thereby maintaining the soil moisture and growth of coconut, and obtaining an unrelenting yield without any production loss [4][5][6][7][8][9][10].…”

Selection of reference genes for quantitative real-time PCR in Cocos nucifera during abiotic stress

“…Therefore, the identification and validation of reference genes for qPCR gene expression studies is critical. In previous research on water relations and irrigation needs in C. nucifera, a crop physiology approach to drought stress was undertaken with measurements such as proline concentration, osmotic potential, leaflet water potential, and leaflet pigment concentration (Carr 2011;Gomes et al 2008Gomes et al , 2010Hebbar et al 2013). In applying molecular biology research techniques to understand coconut stress responses, selection and validation of suitable reference genes for gene expression analysis will comprise an important first step.…”

Evolucion geomorfologica y vegetacion costera de playa Palmeras, Parque Nacional Natural Isla Gorgona, Pacifico Colombiano

“…Especialmente las complejas redes de raíces dan cohesión a los sedimentos y pueden disminuir el impacto de estos eventos. El sistema de raíces de la palma de coco (Cocos nucifera L.) varía según el sustrato en el que se encuentre: en tierra firme la longitud de las raíces alcanza 5 m y en substratos arenosos 7 m. Las raíces pueden ocupar un radio de ~6 m, y como sistema de anclaje de la palma permite la retención efectiva del sustrato donde crece (Carr, 2011).…”