Unit 6: Production of Plantation Crops 6.53 Spacing The optimum spacing is that which will sustain the greatest economic return per unit area. For cocoa, this is affected by intrinsic factors such as planting material and tree vigour, and by environmental variables such as soil type, climate, shade conditions and the prevalence of pests and diseases. In general, close spacing yields higher production in earlier years but, as a close canopy forms and the soil volume is more fully exploited, production differences between close and wide spacing become less marked. Different spacings have been adopted in some areas, where they have become traditional planting practice. The widest spacing (5m x 5m: 400 trees/ha) are found in Sri Lanka, Papua New Guinea and Samoa; the common spacing in Central America and the Caribbean is ca 4111 x 4m (600 trees/ha); spacing tends to be closer in South America (3-4m: 800 trees/ha); while in West Africa seed is frequently planted haphazardly at very close spacing (ca 1.3111: 5900 seed/ha), but many trees die, so that spacing is irregular, with a mature stand density of about 1500 trees per ha. In reviewing results of spacing trials, Wood (1975) concluded that experimental evidence from a range of varieties at different locations suggests that maximum yields are likely to be achieved from spacings of 2.3111 x 3111 - 3m (1100-1900 trees/ha). Weed Control Weed growth must be controlled in young plantations to limit competition, to allow free access to trees and to prevent seedlings being smothered and deformed by vines. Regular and thorough weeding during establishment promotes uniform development and yield. Mechanical cultivation is not suitable for cocoa, as this will damage the shallow feeding roots. A recommended approach is to ring weed seedlings and slash interows. Slashed material maybe usefully applied as mulch to reduce weed growth around developing trees, and to protect the soil surface and improve the soil organic matter status. Herbicides are useful in the initial establishment phase, preparatory to planting cocoa. Since all these formulations are highly toxic, and most are deleterious to cocoa seedlings, their subsequent use demands extreme care. The cost of herbicides limits their widespread use by smallholders, but this approach is successfully used 011 large commercial plantations in Malaysia. Weed growth may be reduced by shade trees, and more particularly by
Unit 6: Production of Plantation Crops 6.54 interplanting crops with dense foliage, such as taro (Colocasia esculenta(L) Schott), ta'amu (Alocasia macrorrhiza(L.) Schott), and manioka (Manihot esculentaGrantz), for temporary shade. Weed control becomes less demanding as trees develop a closed canopy and weed growth is shaded out. This may occur about 2-4 years after planting, depending on trees spacing and the rate of growth.