THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF PINEAPPLE (Ananas comosus var. comosus): A REVIEW

The results of research on the water relations and irrigation need of pineapple are collated and summarised in an attempt to link fundamental studies on crop physiology to irrigation practices. Background information on the centres of origin (northern South America) and of production (Brazil, Thailand and the Philippines) of pineapple is followed by reviews of crop development, including roots, plant water relations, crop water requirements and water productivity and irrigation systems. The majority of the recent research published in the international literature on these topics has been conducted in the United States (Hawaii) and Brazil. Pineapple differs from most other commercial crops in that it has a photosynthetic adaptation (crassulacean acid metabolism (CAM)) that facilitates the uptake of carbon dioxide at night, and improves its water-use efficiency under dry conditions. The crop is propagated vegetatively. The succulent leaves collect (and store) water in the leaf axils, where it is absorbed by surrounding tissue or by aerial roots. There is little published information on the effects of water deficits on vegetative growth, flowering or fruiting. Water stress can reduce the number of fruitlets and the fruit weight. After harvest, one or two ratoon crops can follow. Roots originate from just behind the stem-growing point, some remaining above ground (aerial roots), others entering the soil, reaching depths of 0.85–1.5 m. Root growth ceases at flowering. The ratoon crop depends on the original (plant crop) root system, including the axillary roots. Stomata are present on the abaxial leaf surfaces at relatively low densities (70–85 mm⁻²). They are open throughout the night, and close during the day before reopening in mid-afternoon. The degree to which CAM attributes are expressed depends in part on the location (e.g. tropics or subtropics), and possibly the cultivar, with the total amount of carbon fixed during the night varying from <3% to >80%. There are surprisingly few published reports of field measurements of crop water use and water productivity of pineapple. Two reports show evapotranspiration only occurring during the daytime. There is more uncertainty about the actual water use of pineapple, the value of crop coefficient (Kc) and relative rates of water loss (transpiration) and carbon gain (net photosynthesis), during the daytime and at night, under different water regimes. This is surprising given the amount of fundamental research reported on photosynthesis of CAM plants in general. Although pineapple is mainly a rainfed crop, it is widely irrigated. Drip irrigation is successfully used where the water supply is restricted, the cost of labour is high and cultivation techniques are advanced. Micro-jets can also be used, as can any of the overhead sprinkler systems, provided wind distortion is not a problem. There is a lack of reliable published data quantifying where irrigation of pineapple is likely to be worthwhile, how it is best practised and the benefits that can be obtained. This is remarkable considering the importance of pineapple as an internationally traded commodity.