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Land Selection General requirements
Temperature
The selection of lands for growing pineap-ples will most probably be directed by the temperature profile of the areas being con-sidered. Pineapple growth is almost non-existent below 7°C and above 40°C, so lands where such temperatures occur for long peri-ods 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 maxi-mum at 29°C (Sanford, 1962). The optimaxi-mum temperature for growth is believed to be nearer a mean of 25°C, with an approxi-mately 10°C diurnal temperature range (Neild and Boshell, 1976). This temperature range will ensure that growth rates are bal-anced with a sufficiently high rate of net assimilation to ensure that adequate carbo-hydrate 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 man-agement 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).
Topography
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 mini-mize 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 poten-tial or real soil losses, the limits of topogra-phy 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
*Retired.
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 rain-fall 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 mini-mum loss of soil. The details of constructing such drainage channels vary with the charac-teristics 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 pineap-ple, 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 imper-vious 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 ade-quate soil drainage where high water-tables exist or where infiltration rates may be low.
Soil types
Pineapples have been grown on a wide vari-ety 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 con-verted from farm and pasture-lands.
Soils that are ideal for growth have a high organic-matter content with excellent inter-nal drainage and a high soil air content to provide optimum amounts of water, nutri-ents and oxygen to plant roots. Soils formu-lated 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 pro-portions 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 world-wide (Hepton et al., 1993). Soil amendments should be selected to improve internal char-acteristics towards those of the above-formu-lated 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
Fig. 6.1. Pineapple being grown on steep lands in Hekou County, Yunan Province, China.
the growth of water moulds, such as Phytophthora and Pythium species.
Sunlight
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 peri-ods 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 trop-ics 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 accumu-lation and subsequent fruit size and yield.
Water
As discussed elsewhere (Malézieux et al., Chapter 5, this volume), pineapple is uniquely adapted to grow well in areas with Fig. 6.2. Subsoilers used in Queensland, Australia, and in Hawaii, to improve soil drainage (photos courtesy of D. Bartholomew (left) and K.G. Rohrbach (right)).
Fig. 6.3. Ridger used in South Africa to facilitate drainage in heavy soils. Protrusions on the roller establish the plant spacing. (Photo courtesy of Graham Petty.)
low rainfall. The minimum water require-ment 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 exces-sive 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.
Soil surveys
When areas of land larger than 8 ha (20 acres) are being evaluated for pineapple planting, a soil survey should be conducted.
A survey will provide important information regarding the topography, soil profile and subsurface variations in soil structure, soil chemistry and drainage. This information will be vital in determining the need for con-touring and other erosion-control measures, surface drainage, subsoiling, depth of culti-vation, need for bed formation, nutrient requirements and other cultural practices that can be influenced by soil conditions.
The surveys should be conducted by a person familiar with standard survey proce-dures, including site preparation and soil classification. The survey reports should include any history of past usage, including cropping and soil management. The physical description of the soil by profile should be supplemented with information on physical and chemical analyses to allow appropriate agricultural practices to be developed.
Maps should be prepared that identify boundaries of the growing areas, areas par-ticularly susceptible to erosion, waterways and other drainage channels, roads and pathways, particularly if these are used by the public. The approximate boundaries of each soil type should be identified according to soil classification. All of this information should overlay a topographical map of the area to facilitate development of field layout and drainage systems.
Residential and other environmentally sensitive areas should be identified to facili-tate compliance with local regulations.
Soil sampling
A composite sample that adequately repre-sents the soil in the field must be taken so that the results can be used to develop soil-management information for the crop. For the preparation of a composite sample, usually 15–20 core samples are taken in a random pat-tern from an area of no more than 8 ha (20 acres). Composite samples must be prepared and maintained in a manner that will not com-promise the results. Guidelines for sampling and handling soil samples can be obtained from the soil science departments of most uni-versities or analytical laboratories, and analy-ses can be performed for modest fees.
Where soil surveys show that more than one distinct soil type exists in an area to be farmed, each soil type should be sampled separately if the areas are large enough to be fertilized separately. Areas that are not typi-cal of the general area being sampled should be avoided or, if resources permit, sampled separately. Problem areas should be sampled separately, and additional samples may be required from the subsoil in these areas.
Topsoil and subsoil samples should be analysed separately and compared with results from the more typical areas.
Soil analyses
Soil texture
Soil A and B horizons should be evaluated for soil texture. Aspects that can be docu-mented include: (i) coarse fragment analysis;
(ii) particle size by hydrometer and hand-sieving; (iii) texture by feel; (iv) moisture content; (v) water-holding capacity (water content at field capacity and at 1.5 MPa pres-sure); and (vi) bulk density.
Soil pH
Soil pH is measured on a saturated paste.
This aspect of soil analysis is important for pineapple culture, as serious problems can be associated with alkaline soils. The most serious is the proliferation of water moulds, Phytophthora spp. and pythiaceous fungi, which are parasitic on pineapple roots and
stems. Soils of alkaline pH may also limit the availability of important nutrient elements, with iron being a notable example.
Cation exchange capacity (CEC) CEC may be estimated using the NaOAc/NH4OAc replacement method. CEC data provide a measure of the soils’ ability to hold nutrients in a form available for uptake by the plant, can have an impact on the fre-quency of fertilizer applications and may also indicate whether the fertilizer should be applied to the soil or as a foliar spray.
Organic matter
The organic-matter content can be measured by ashing the soil, with the volume of organic matter being estimated from the loss of weight. As mentioned earlier, pineapple plants respond favourably to soils with a high percentage of organic matter. This is not to be confused with crop residue or other organic material that has not undergone complete decomposition by composting or other means that result in a stable C/N ratio in the soil.
Total elemental composition
Soil elemental composition can be measured by HNO3/HClO4digestion and analysis by inductively coupled plasma (ICP) spectrom-etry. Metals analysis can be made for Fe, Zn, Cu, Mn, Cd, Cr, Ni and Pb and the water-soluble elements Ca, Mg, Na, K, S and B can be determined.
Nitrogen in the soil can be measured by the Kjeldahl method. Not all soil nitrogen is fully available, though mineralization gradu-ally releases nitrogen in organic matter.
Nitrogen in the mineral form should eventu-ally be replaced to maintain an adequate supply for plant nutrition.
Land and Soil Preparation Land clearing, field layout and bed design If the site has not been cropped previously, the first operation will probably be to remove brush and trees. After the fields have
been surveyed to establish the slope, need for and frequency and position of drainage channels, these channels should be installed so as to effectively capture and remove excess rainfall in a manner that minimizes erosion. If drainage channels discharge into adjacent waterways, the need for permanent drop structures should be evaluated.
Where rock removal is necessary, rocks larger than about 30 cm (1 ft) in diameter should be removed after ploughing or sub-soiling and after final land preparation. Rock removal from stony fields can be expensive and, in some cases, specialized equipment has been developed to mechanize the removal process (Fig. 6.4). These rocks may be used for construction of drop structures or other field construction or, if excessive, they may be left in piles.
In areas where field operations are machine-assisted, planting areas may be laid out in blocks separated by roads. The dimen-sions of the blocks are designed to accommo-date the equipment, while effectively accomplishing the required field operations.
Where boom sprayer equipment is to be used, block size is usually twice as wide as the spray boom is long.
Once the basic tillage operations (Fig. 6.5) have been performed, raised planting beds may be formed (Fig. 6.3) if there are known economic advantages. In most cases, pineap-ple plant growth is enhanced by planting on raised beds due to the increase in the volume of topsoil available to the root system, enhanced aeration and superior drainage.
Raised beds may or may not be covered with plastic mulch, usually depending on the need for fumigation. In some cases, where capture of sparse rainfall is important, slightly depressed beds direct limited rainfall or overhead irrigation to the planting line.
Despite the advantages of raised beds, they are not used where the cost of preparation exceeds the economic benefit.
Treatment of previous crop residues
Knock-down and incorporation Because of its leaf morphology and succu-lence, pineapple plants are slow to desiccate,
and shoots produced from living plant stems incorporated into the soil can be a serious weed in fields. Thus, it is common to chop standing plants by discing or power flail to
hasten their desiccation and decomposition.
In the peat soils of Malaysia, plants are killed with gramoxone to hasten their desiccation.
Once desiccated, plant residues may be Fig. 6.4. Rock picker used in northern Queensland, Australia, to remove large rocks from pineapple fields prior to planting (photo of Duane Bartholomew).
Fig. 6.5. A, Large mouldboard plough used in Hawaii to incorporate dried plant trash; B, four-wheel-drive tractor and heavy disc used for primary preparation after ploughing (photo courtesy of CAMECO Corp.);
C, rototiller used to improve soil tilth after primary tillage operations (photo courtesy of Graham Petty);
D, spring-tooth harrow used for land preparation in South Africa (photo courtesy of Graham Petty).
burned under dry conditions or incorporated into the soil, provided there is sufficient moisture and time for decomposition.
Pineapple plant residue may also be har-vested for animal feed or for by-products, such as fuel, fibre or extracts, such as the enzyme bromelain. Removing the crop residue may help to shorten the crop intercy-cle for timely production schedules.
However, repeated removal of pineapple residue depletes the soil of essential nutri-ents and organic matter. Soils with poor structure, low native organic matter and low CEC benefit most from residue incorporation and are most adversely affected by residue removal. The benefits of residue incorpora-tion can accrue over several crop cycles.
Well-aggregated soils with a stable organic-matter fraction and a comprehensive supply of nutrients may show little benefit from residue incorporation, at least in the short term.
Conventional tillage
Poor tilth and impediments to drainage are especially unfavourable to pineapple. The chief objective of tillage is to achieve excel-lent soil tilth to improve contact with the planting material and for rapid and sus-tained root development. Tillage should achieve a permeable soil profile that is free of rocks and large clods and a homogeneous distribution of decomposed residue, amend-ments and fertilizers. Where fumigation for nematode control is essential, fine tilth must be achieved for effective distribution of the fumigant.
Compaction due to residue management, tillage operations and in-field traffic may easily become counterproductive.
Compaction needs to be avoided or mini-mized by selecting the right equipment according to soil type, internal soil structure, soil moisture, organic-matter content and the time available to prepare the land.
Subsoilers are used to break up impervi-ous or compacted internal layers to improve drainage without changing layering of hori-zons in the soil profile (Fig. 6.2). Deep ploughing may be used where mixing or redistribution of nutrients or soil layers
results in an improved planting and growing environment. Harrows and discs (Fig. 6.5) are used to break up clods to provide a suit-able tilth for planting. Rollers, cultipackers, rototillers and levelling boards may be used to finish the tillage operations. These opera-tions will be followed by bed-forming, pre-plant fertilizer application and fumigation, with mulch laying, where these operations are appropriate.
Minimum tillage
The practice of minimum tillage is becoming increasingly popular because it can reduce the cost of land preparation, conserve organic matter from the previous crop, reduce moisture loss during land prepara-tion, preserve the balance of microflora and microfauna in the soil profile and reduce soil erosion. However, there may be valid rea-sons for not using minimum tillage. For example, tillage may be necessary to facili-tate the control of ants and mealybugs, which are intimately associated with mealy-bug wilt, and excellent tilth is essential to good distribution of soil fumigants used to control nematodes. In some soils, tillage may be necessary to provide tilth that will allow planting.
In those soils where tillage is not a prereq-uisite for subsequent operations, the previ-ous crop residues may be physically or chemically killed and allowed to form an organic mulch through which the pineapple plants are planted. If minimum tillage prac-tices are used, special consideration should be given to plant nutrition. Preplant incorpo-ration of plant nutrients may not be possible and the plant nutrients may not be uni-formly distributed in the root zone. These limitations may place a greater burden on timely application of foliar and soil-applied nutrients.
Soil amendments and fertilizers Soil amendments, such as lime and organic matter, influence plant growth indirectly by improving the physical or chemical condi-tion of the soil, though amendments
gener-ally also provide plant nutrients. Composted animal manures provide organic matter and improve soil structure, while supplying plant nutrients. Lime adjusts soil pH, as well as supplying calcium, and, if from dolomite, it also supplies magnesium. Pineapple root development can vary dramatically among locations, so a site-specific understanding of root development is important to determine whether or not plants will respond favourably to the use of soil amendments.
gener-ally also provide plant nutrients. Composted animal manures provide organic matter and improve soil structure, while supplying plant nutrients. Lime adjusts soil pH, as well as supplying calcium, and, if from dolomite, it also supplies magnesium. Pineapple root development can vary dramatically among locations, so a site-specific understanding of root development is important to determine whether or not plants will respond favourably to the use of soil amendments.