Planting density

Many factors are involved in the determination of planting density and, as a result, densities may vary from as low as 29,000 plants ha-1 (12,000 plants acre-1) to as high as 86,000 plants ha-1 (35,000 plants acre-1). Both environment, especially solar radiation, and nutrition influence plant growth and the competition between plants for available resources. Marketing is an important consideration for the grower, because plant growth rates and plant size at the time of forcing influence fruit weight and fruit-size distribution. Densities are selected to manage these relationships with a view to effecting the desired production.

Sunlight intensity and duration determine the amount of energy available for photosynthesis. Areas with long periods of cloud-free days will support greater carbohydrate assimilation than will cloudy areas. Seasonal variations will be more accentuated in those growing areas farther away from the equator. Where seasonal changes are large, density changes on a seasonal basis may need to be considered for optimum production.

Experiments conducted on the effect of density on average fruit weight and yield have shown quite predictable results. Average fruit weight decreases linearly with increasing density, but the effect is variety-and site-specific (Fig. 6.10). For 'Smooth Cayenne' in Hawaii, fruit weight decreases by 2.4% per 1000 increase in plants per acre over a wide range of densities. Total yield per unit land area generally increases curvi-linearly with increasing density (Fig. 6.11), though some studies show that yields decline at very high plant populations. Typical plant population densities for 'Smooth Cayenne' range from about 60,000 to 80,000 plants ha-1 (24,000-32,000 plants acre-1). The optimum density for a given farm or region and variety must be determined by the available technology, environmental resources and market requirements.

Fig. 6.10. Effect of plant population density on average pineapple fruit weight of 'Queen' grown in Ghana (Norman, 1978), 'Singapore Spanish' grown in Malaysia (Wee, 1969) and 'Smooth Cayenne' grown in Queensland, Australia (Scott, 1992), and Swaziland (Dodson, 1968). Regressions are 'Queen', y = -9 x 10-6x + 1.59, R2 = 0.93, n = 9; 'Singapore Spanish', y = -3 x 10-6x + 1.16, R2 = 0.835, n = 6; Queensland 'Smooth Cayenne' (y = -3 x 10-5x + 4.05, R2 = 0.98); Swaziland 'Smooth Cayenne', 400N, y = -6.8 x 10-6x + 2.08, R2 = 0.95; 200N, y = -7.6 x 10-6x + 1.84, R2 = 0.96, n = 5, where y is estimated fruit weight in kg and x is plants ha-1.

Fig. 6.10. Effect of plant population density on average pineapple fruit weight of 'Queen' grown in Ghana (Norman, 1978), 'Singapore Spanish' grown in Malaysia (Wee, 1969) and 'Smooth Cayenne' grown in Queensland, Australia (Scott, 1992), and Swaziland (Dodson, 1968). Regressions are 'Queen', y = -9 x 10-6x + 1.59, R2 = 0.93, n = 9; 'Singapore Spanish', y = -3 x 10-6x + 1.16, R2 = 0.835, n = 6; Queensland 'Smooth Cayenne' (y = -3 x 10-5x + 4.05, R2 = 0.98); Swaziland 'Smooth Cayenne', 400N, y = -6.8 x 10-6x + 2.08, R2 = 0.95; 200N, y = -7.6 x 10-6x + 1.84, R2 = 0.96, n = 5, where y is estimated fruit weight in kg and x is plants ha-1.

Fig. 6.11. Effects of plant population density on pineapple fruit yield as shown by the authors or calculated from their average fruit-weight data. Data are for 'Queen' grown in Ghana (Norman, 1978), 'Singapore Spanish' grown in Malaysia (Wee, 1969) and 'Smooth Cayenne' grown in Queensland, Australia (Scott, 1992), and Swaziland (Dodson, 1968).

Fig. 6.11. Effects of plant population density on pineapple fruit yield as shown by the authors or calculated from their average fruit-weight data. Data are for 'Queen' grown in Ghana (Norman, 1978), 'Singapore Spanish' grown in Malaysia (Wee, 1969) and 'Smooth Cayenne' grown in Queensland, Australia (Scott, 1992), and Swaziland (Dodson, 1968).

Fig. 6.12. Effect of average night temperature on stem dry matter (DM) content as a percentage of total plant dry matter and on fruit harvest index calculated from plant fresh weight at forcing and fruit weight at harvest (redrawn from Hepton et al., 1993).

Ratios of fruit mass at harvest to plant mass at forcing (harvest index) have been measured in various regions where pineapple is grown. The harvest index can be as low as 0.4 in areas with warm nights and fast growth rates and can exceed 1.0 where irra-diance is high and night temperatures are cool. Where growing medium and nutrition were controlled in a variety of climatic con ditions (Hepton et al., 1993), stem dry-matter content as a percentage of total plant dry matter and harvest index decreased as average night temperature increased (Fig. 6.12). Thus, stem dry-matter content has a strong influence on the harvest index of 'Smooth Cayenne' pineapple (Fig. 6.13). These factors should be taken into consideration when selecting a planting density.

Stem dry matter/plant dry matter (%)

Fig. 6.13. Effect of stem dry-matter content on harvest index calculated from plant fresh weight at forcing and fruit weight at harvest (redrawn from Hepton et al., 1993).

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  • elsa
    What are important factors for planting pineapples?
    4 years ago

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