The selection of lands for growing pineapples will most probably be directed by the temperature profile of the areas being considered. Pineapple growth is almost nonexistent below 7°C and above 40°C, so lands where such temperatures occur for long periods of time are unsuitable if production of the crop is to be economically viable. Night temperatures below 7°C are tolerated and may promote flower induction, a sometimes beneficial effect, but freezing temperatures must be avoided.
Growth of leaves reaches a maximum at about 32°C and root growth reaches a maximum at 29°C (Sanford, 1962). The optimum temperature for growth is believed to be nearer a mean of 25°C, with an approximately 10°C diurnal temperature range (Neild and Boshell, 1976). This temperature range will ensure that growth rates are balanced with a sufficiently high rate of net assimilation to ensure that adequate carbohydrate reserves are maintained by the plant, especially near the time of flower induction. While pineapple has relatively high maximum and minimum temperatures for shoot and root growth, the plant is very adaptable and is grown in a very wide area from the Tropic of Cancer to the Tropic of Capricorn, and beyond this area where local temperatures are favourably moderated by unique geographical features. Unique management problems may be encountered when temperatures are considerably below or above the optimum range (see Malézieux et al., Chapter 5, and Bartholomew et al., Chapter 8, this volume).
Protection of the soil resource from erosion is an important consideration in all agriculture and, for that reason, minimally sloping lands should be selected for pineapple culture. Slopes of no more than a few per cent minimize soil losses, while lands with steeper slopes require expensive drainage channels, contouring and other protective measures to sustain the soil resource.
In the absence of consideration of potential or real soil losses, the limits of topography are usually a result of workers' ability to plant, maintain and harvest the crop. In areas that are exclusively managed with hand labour, pineapples can be grown in fields that are extremely steep (Fig. 6.1), but, where
© CAB International 2003. The Pineapple: Botany, Production and Uses
(eds D.P. Bartholomew, R.E. Paull and K.G. Rohrbach) 109
mechanization is a requirement for land preparation, maintenance or harvesting, slopes are limited by the requirements of the equipment. Slopes of nearly 40% are farmed with medium-sized machinery in Queensland, Australia, with good results, though erosion losses from such fields can be very high (El-Swaify et al, 1993; Ciesiolka et al, 1995).
Most pineapple-growing areas are laid out with consideration of the impact of rainfall on erosion and drainage. In areas that may experience heavy rainfall or have low infiltration rates, or both, drainage channels should be constructed at intervals that will accommodate the surface runoff and allow this runoff to move off the field with a minimum loss of soil. The details of constructing such drainage channels vary with the characteristics of the soil and the slope of the land (El-Swaify et al, 1982; Hudson, 1995).
Drainage and the removal of water are critical to the successful growing of pineapple, as the root system is intolerant of poorly aerated soils. Areas to be avoided are those that accumulate standing water or that have internal barriers to soil moisture movement, such as plough pans or compacted or impervious soil layers. Where drainage is poor, sub-soiling (Fig. 6.2), ripping or installation of internal drainage may be necessary. Ditching and ridging (Fig. 6.3) are used to provide adequate soil drainage where high water-tables exist or where infiltration rates may be low.
Pineapples have been grown on a wide variety of soils, from organic peat soils, as in Malaysia, and volcanic ash soils in Hawaii, many Caribbean islands and parts of the Philippines to the very sandy soils found in parts of southern Queensland and northern South Africa. In between are a variety of weathered and secondary-deposit soils, some with forest topsoils and others converted from farm and pasture-lands.
Soils that are ideal for growth have a high organic-matter content with excellent internal drainage and a high soil air content to provide optimum amounts of water, nutrients and oxygen to plant roots. Soils formulated by growers who raised pineapples in the late 1700s in glasshouses in England used a combination of rotted oak leaves, sheep manure, sod and sand, with the proportions being varied by season (Speechly, 1796). Recently, an artificial growing medium, composed of peat moss and vermi-culite and fertilized with a complete nutrient solution, has supported outstanding growth of pineapple in a variety of locations worldwide (Hepton et al., 1993). Soil amendments should be selected to improve internal characteristics towards those of the above-formulated media. Soils should have a neutral to acidic pH, although pineapples will grow in slightly alkaline soils if calcium levels are not too high and soil moisture does not favour
the growth of water moulds, such as Phytophthora and Pythium species.
Pineapple is most productive in areas with extensive sunlight. An ideal climate will have temperatures below 32°C and cloud-free days; however, most climates will have periods of seasonal cloudiness. High irradiance in combination with high air temperatures lead to sunburn, both on the leaves that are directly exposed and on fruit that may lodge at angles that increase exposure. There is no day-length requirement for growth or flower ing. The day lengths of pineapple-growing areas near the equator vary less than an hour from winter to summer, while near the tropics of Cancer and Capricorn the variation is somewhat more than 2 h. The variation in irradiance and temperature across the range of latitudes where pineapple is grown has a significant impact on carbohydrate accumulation and subsequent fruit size and yield.
As discussed elsewhere (Malezieux et al., Chapter 5, this volume), pineapple is uniquely adapted to grow well in areas with low rainfall. The minimum water requirement for unrestricted growth is about 5 cm (2 in.) of water per month; this small amount of water is most efficiently utilized when applied to the root zone in beds covered with an impervious mulch at intervals that will keep the root zone adequately supplied with moisture without loss through excessive application. Where rainfall is less than 5 cm per month, growth will be reduced and either the crop cycle will be lengthened or average fruit weight will be reduced.
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