Pineapple (Ananas comosus) is a perennial crop grown for its fruits and used as a fresh and processed product. World production is about 13.7 million tons fresh fruit.(FAOSTAT, 2001).

The origin of the pineapple is still uncertain but the Parana-Paraguay Basin has been considered as a possible area. For good growth pineapple requires mean daily temperatures of 22 to 26°C with an optimum of 23 to 24°C. Mean daily maximum and minimum temperatures of 30 and 20°C respectively for the whole growing period are considered optimum. Temperatures below or above this range affect fruit quality or the acid and sugar content.

The crop is grown between 31°N and 34°S, primarily in regions with high relative humidity. A combination of optimum temperature and high humidity results in soft, large leaves and juicy fruits, low in acid content. Fruits ripening in periods with cool temperatures and low radiation levels, e.g. in winter or at high altitudes, are of inferior quality because of poor shape for canning. Requirements for canning are: a cylindrical shape, fruit eyes of a relatively shallow surface and a small fruit core in relation to the fruit.

Pineapple can grow on a wide range of soils but a sandy loam texture is preferred. Optimum soil pH is 4.5 to 6.5. The soil should have a low lime content. The crop is sensitive to waterlogging and therefore requires a well-drained soil with good aeration. For high production the fertilizer needs are 230 to 300 kg/ha N, 45 to 65 kg/ha P and 110 to 220 kg/ha K.

Pineapple is usually grown in double rows on raised beds. With a spacing of 0.6 x 0.3m in beds 0.75 to 0.90m apart, plant population is about 50000 per ha. Shading is sometimes used where temperatures are high and radiation intense to protect the crop from scorching. The crop is multiplied using slips, crowns and shoots or suckers, but in comparison with using suckers as planting material, the period from planting to harvest is about 20 percent longer when slips are used, and about 35 percent longer when crowns are used. Use of different planting material allows a manipulation of the crop growing period and particularly in selection of the time of harvest when climatic conditions are favourable for high quality fruits. Normally the plant crop is followed by one ratoon crop, but when climatic conditions are favourable, the crop will continue to bear fruits but quality rapidly declines after the first ratoon. However, in warm tropical climates, e.g. at low altitudes near the equator, no ratoon crop is possible because suckers do not develop. The period from planting to harvest of the plant crop is 1 to 2 years and of the ratoon crop 9 months to 1.5 years depending on planting material and climate.

The flower initiation in pineapple is induced by low temperature, water deficit or hormone spray; the latter results in a uniform fruiting and harvest period.

Plant crop, first ratoon and second ratoon (Collins, 1960)

¹ The pineapple plant has very low transpiration because it closes its stomates during the day and opens them during the night. Therefore, the majority of ETc from pineapple is evaporation from the soil. The Kc mid < Kc ini since Kc mid occurs during full ground cover so that soil evaporation is less. Values given assume that 50 % of the ground surface is covered by black plasic mulch and that irrigation is by sprinkler. For drip irrigation beneath rhe plastic mulch Kc's given can be reduced by 0.10.

Crop water requirements (ETm) for high production are very different from those of most other crops. Because there is a suspension of transpiration during the day, maximum evapotranspiration is low and varies between 700 and 1000 mm per year The crop coefficient (kc) relating reference evapotranspiration (ETo) to ETm is about 0.4 to 0.5 for the total growing period.

The following figure shows growth periods of a 20-month pineapple (after E.A.C., 1977)

Pineapple can survive long dry periods through its ability to retain water in the leaves which is used during these periods. Also due to its low water use, the plant can survive on a small depth of stored soil water. However, the crop is sensitive to water deficit, especially during the vegetative growth period, when the size and fruiting characteristics are determined. Water deficits retard growth, flowering and fruiting. Water supply during this period should meet full water requirements of the crop. Water deficit at flowering has a less serious effect and may even hasten fruiting and result in uniform ripening. An ample water supply at flowering will lead to vigorous stem growth and a large core which is disadvantageous when the fruit is used for canning. Frequent irrigation or rain at the time of harvest may cause deterioration of the quality of the fruit and make the crop susceptible to the fungus causing heart rot. In addition, waterlogging affects fruit quality. Where water supply is limited, mulching is practised to reduce soil evaporation and soil temperature. Dew has been found to contribute to meeting the wafer requirements of the crop.

The rooting system of pineapple is shallow and sparse. In deep soils, maximum root depth may extend up to 1m but roots are generally concentrated in the first 0.3 to 0.6 m, from which normally 100 percent of the water is extracted (D = 0.3-0.6 m). Under conditions when maximum evapotranspiration is 5 to 6 mm/day, water uptake starts to be reduced when about 50 percent of the available soil water has been depleted (p = 0.5).

Adequate water supply is essential particularly during the vegetative period. The interval of application can be based on the prevailing rate of maximum evapotranspiration (ETm) and the fraction (p) of the total available soil water. Where rainfall is small and irrigation water supply is restricted, irrigation scheduling should be based on avoiding water deficits during the period of vegetative growth (1). Supply of water can be restricted during the period of ripening (4) whereas some water savings can be made by allowing higher depletion levels up to 75 percent during flowering (2). During the month prior to harvest irrigation is discontinued. The method of irrigation is mostly by sprinkler.

The fruit contains about 80 to 85 percent water and 10 to 14 percent sugar. Irrigation has an effect on the sugar/acid ratio, particularly in the period prior to harvest when frequent high irrigation decreases the sugar content. The infestation by soil-borne fungus diseases is increased. Under commercial production, weight per fruit is about 1. 5 to 1.8 kg, and total yield between 75 and 90 ton/ha fresh fruit. The water utilization efficiency for harvested yield (Ey) for fresh fruit is about 5 to 10 kg/m³for the plant crop and 8 to 12 kg/m³for the first ratoon crop.