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Acacia holosericea Cunn. ex G. Don |
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Leguminosae
Common names Fish poison wattle, soapy wattle |
Author: Le Houérou
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A. holosericea has recently been split into 4 taxonomic specific entities (Maslin & Thompson, 1992) :
As a result of this taxonomic split, it is often difficult to figure out from reports and publications which of the new entities is meant when dealing with the pre-1992 trials in the Sahel, as these taxa are morphologically very close ; of necessity, they must therefore be treated globally, when the Sahel is concerned., albeit there being also substantial ecological requirement differences between them. For the analysis of these morphological and ecological differences see Maslin & Thompson, 1992 and Dommergues et al., 1999. Shrub to small tree 2-5 m high with erect to fastigiate branches ; rarely a tree up to 12 m high. Twigs are angular, covered with a whitish down, often of a fawn hue. Phyllodes are 10-20 cm long and 1.5-5.0 cm wide, covered with silky, flattened hair, provided with a mucronate tip. There are three conspicuous major nerves the central one joining with the 2 lateral at the bottom and extending to the mucro at the tip. Secondary nerves anastomosing to form a reticulate network, with a small gland at the bottom of the apex on the upper face of the blade. Flowers golden-yellow in spikes 2-5 cm long ; peduncles 3-7 mm ; minute, spathulate, early deciduous bractlets 1 mm long. Pods rolled and irregularly twisted 2..5-4 mm wide, leathery, seeds with a bright yellow aril. Life span ca 10 years, propagation by seeds only, with a moderate ability to coppice and a weak ability to suckering. It requires high temperatures and no frost ("m" > 8-10°C). In its home land A. holosericea occurs under MAR rainfall belts of 300 mm and up to 600 and above, with a 3-4 month summer rainy season. It has been successfully established in many places in Sahel with a MAR above 500 mm. It is sensitive to alkalinity and to salinity. A. holosericea appears to be less demanding in phosphorus than native acacias of Sahel, responding to very low P fertilization or even to endomycorrhyzation only (Dommergues et al. ,1999). A. holosericea is native of northern West Australia and southern North Territory. It has been successfully established in the Sahel, Senegal, Niger, Burkina Faso, North Cameroun, Nigeria, and also to East African arid lands. Wood is hard, with a density of 0.87, excellent fuelwood in spite of its fast growth ; it appears this species is particularly fit for protection, rehabilitation and afforestation projects in the South Sahelian and North Sudanian ecozones, (Souvannavong & Fremond, 1992). Productivity in the South Sahel conditions is high and growth much faster than in any native acacias. The young trees may reach reach 3 m in 2 years, average phyllode production per tree is ca 2.6 kg DM / annum in the fourth year of age at the first thinning, which for a density of 1111 trees per ha (3 x 3 m) corresponds with 2,880 kg forage DM / ha / yr and 3,330kg / ha / yr of dry wood (Cossalter, 1987, Wickens et al., 1995). Rain use efficiency is thus 6,210 kg DM / 550 mm = 11.3 kg DM / ha / yr / mm., which is over three-fold the rangeland productivity under similar ecological conditions and appropriate management (Le Houérou & Hoste, 1977 ; Le Houérou, 1980 f, 1984, 1989 a, Le Houérou et al., 1988). This wattle is also used as an effective secondary windbreak in farmland and for sand dune fixation in the Groundnut Basin of Senegal ; its ornamental value is used in street and amenity plantations, roasted seeds are edible to humans, they are rich in CP, Fat, NFE and Energy (House & Harwood , 1992 ; Harwood, 1994). The wood is fairly resistant to termites, but the roots are very sensitive to pathogen gall-forming nematodes and therefore A. holosericea should be avoided as a windbreak in irrigated farming, as it may become, like Prosopis juliflora, a liability to crops as a host for vegetable pest nematods (Dommergues et al., 1999). Nutritional Quality and Animal Production Forage production is high in quantity but rather poor in quality, unlike most native acacias A. holosericea keeps its phyllodes during the dry season, it may thus play a role in dry season feeding of stock, albeit the CP content is low. Predicted digestibility of the DM is 40 % + / - 5, and CP content 12 % + / - 2 and phosphorus 0.08 % + / - 2, in both pods and foliage (Vercoe, 1987, 1989).
Hamel 1980 ; Simmons 1981 ; Cossalter 1985 ; Cossalter 1987 ; Vercoe 1987 ; Vercoe 1989 ; Turnbull 1986 ; Turnbull 1987 ; Goodchild & Meniman 1987 ; Chege & Stewart 1991 ; Kimondo 1991 ; Maslin & Thompson 1992 ; Souvannavong & Fremond 1992 ; Rinaudo 1992 ; Rinaudo 1995 ; Thompson 1992 ; Harwood 1993 ; Harwood 1994 ; Maslin & McDonald 1996 ; Wickens et al. 1995 ; Dommergues et al. 1999. |