Knock-down and incorporation
Because of its leaf morphology and succulence, pineapple plants are slow to desiccate,
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).
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 burned under dry conditions or incorporated into the soil, provided there is sufficient moisture and time for decomposition.
Pineapple plant residue may also be harvested 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 intercycle for timely production schedules. However, repeated removal of pineapple residue depletes the soil of essential nutrients 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 incorporation 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.
Poor tilth and impediments to drainage are especially unfavourable to pineapple. The chief objective of tillage is to achieve excellent soil tilth to improve contact with the planting material and for rapid and sustained root development. Tillage should achieve a permeable soil profile that is free of rocks and large clods and a homogeneous distribution of decomposed residue, amendments 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 minimized 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 impervious or compacted internal layers to improve drainage without changing layering of horizons 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 suitable tilth for planting. Rollers, cultipackers, rototillers and levelling boards may be used to finish the tillage operations. These operations will be followed by bed-forming, pre-plant fertilizer application and fumigation, with mulch laying, where these operations are appropriate.
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 preparation, preserve the balance of microflora and microfauna in the soil profile and reduce soil erosion. However, there may be valid reasons for not using minimum tillage. For example, tillage may be necessary to facilitate the control of ants and mealybugs, which are intimately associated with mealybug 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 prerequisite for subsequent operations, the previous 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 practices are used, special consideration should be given to plant nutrition. Preplant incorporation of plant nutrients may not be possible and the plant nutrients may not be uniformly distributed in the root zone. These limitations may place a greater burden on timely application of foliar and soil-applied nutrients.
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