Acacia angustissima, A. boliviana and A. villosa
Acacia saligna - Golden Wreath Wattle
Chamaecytisus palmensis, Tagasaste or Tree Lucerne
There are many species of multipurpose forage tree legumes in use throughout the tropical and subtropical regions of the world. In the preceding sections of Chapter 2, the most well known species are described but many others have shown potential for exploitation while others have yet to be identified as valuable multipurpose forage trees. Brewbaker (1986) listed about 80 species which are known to serve as animal fodder. One approach to developing new material is to encourage intensive activity with well known species as their genetic reservoirs of diversity have hardly been tapped. Another approach is to identify promising new species from other genera to increase the number of species in common use and broaden the genetic base.
It is not possible to examine all 80 species in this section but eight selected species representative of those which have shown potential, or are currently used in certain regions, are now reviewed in more detail. A tabular summary of the characteristics of the eight species is given in Table 2.7.1.
All three of these species are closely related and are often confused botanically. They are virtually interchangeable with respect to habit, environmental adaptation and productivity. They have all received increased attention as alternatives to Leucaena leucocephala following its devastation by the psyllid insect. Acacia angustissima will be described here as representative of the group.
Acacia angustissima is a multi-branched, thornless shrub or small tree which grows to a maximum height of about 5 m (Figure 2.7.1). Flowers are mimosoid and it is a prolific seed producer. The species is native to Central America and it is now common in southeast Asia, particularly Indonesia. It is well adapted to free draining acid, infertile soils and shows excellent drought tolerance. It retains green leaf in the long (8 month) dry season in Timor, Indonesia (Field 1989).
Table 2.7.1. Characteristics of eight forage tree legume species.
Fig. 2.7.1. Acacia angustissima growing near Darwin, Australia.
Its branching habit enables it to withstand frequent cutting or defoliation. Cutting heights of 50-100 cm at frequencies of 8-10 weeks have been used in a number of regions (Benjamin 1988). Leaf yields of up to 5 t/ha/year have been reported (Benjamin 1988).
There is conflicting information regarding its palatability and intake by livestock. Reports from some areas in Indonesia suggest its palatability is low although condensed tannin levels in the leaf are not especially high (up to 6%) (Akin et al. 1989). The same authors reported an in sacco in vitro dry matter digestibility of 48% after 24 h indicating that digestibility may be low. In other areas, however, the leaf is reported to be well eaten by livestock and it is regarded as an important source of forage (Keoghan 1987). In central Queensland weaner steers were given access to a 2 ha area planted to A. boliviana CPI 40175 in rows 3 m apart. In two weeks, two thirds of the leaf material had been eaten (C. Middleton, unpublished data).
In Timor, Indonesia, Acacia villosa is used as a fallow species to provide fuelwood and to enrich the soil prior to cropping. In Lombok, it is used on sloping sites dominated by Imperata grassland to prevent soil erosion and stabilise the landscape (Field 1989). Nitis (1986) has used it in Bali as the shrub stratum in a 3-tier forage production system using grasses, herbaceous legumes, forage shrubs and forage trees.
Acacia saligna is a dense bushy shrub 2-5 m tall with long straggling branches. Phyllodes are dark green, long (up to 20 cm) and narrow. It occurs naturally in the southwestern comer of Western Australia but has been introduced to other regions of Australia and to many other countries. It grows on a wide range of soil types but is outstanding on sandy coastal plains and sand dunes. It is used extensively for sand dune stabilisation and reclamation (NAS 1980). It prefers an annual rainfall range of 350-600 mm but will grow well in areas with rainfall as low as 250 mm and as high as 1,200 mm. It is moderately tolerant of soil salinity. The phyllodes of A. saligna are often used as supplementary feed for sheep and goats in countries such as Libya (El Lakany 1986). Crude protein content of phyllodes varies from 12 to 16% and in vitro dry matter digestibility has been measured at 40% (Vercoe 1989). Le Houerou (1984) recorded daily consumption rates of 1.6 kg/head/day for sheep over prolonged periods without apparent detrimental effects.
It is reasonably tolerant of browsing and defoliation and some reports indicate it can be completely defoliated without harming the plant (NAS 1980). However, Gutteridge (1990) reported 50% mortality with regular defoliation over 4 years. The wood is sappy and light and reported not to be particularly good as fuel although in many arid regions, plantations of A. saligna have been established for fuelwood as it is the only species which is fast growing and productive in such unfavourable sites.
Tagasaste is a member of the Fabaceae family and is native to the Canary Islands. It holds promise for use in tropical highlands, Mediterranean climates and temperate regions. It grows to a height of 5-6 m, is thornless and generally well branched. Flowers are white and seed production is prolific.
It is suited to sandy well drained soils of pH range 5-7. It is very susceptible to root rot fungus on poorly drained soils such as in southeast Queensland on a grey podzolic duplex soil where 100% mortality of plants occurred within 2 years (Gutteridge 1990). Responses to applications of superphosphate have been obtained on phosphorus deficient soils (Snook 1982). It is reasonably drought tolerant because of its deep taproot and grows well in the rainfall range 350-1,600 mm per annum.
In the Canary Islands, farmers are completely dependent on tagasaste for forage during the long dry summers. In Australia, edible dry matter yields of up to 11 t/ha/year have been achieved under favourable conditions (Snook 1982). Radcliffe (1985) obtained 4-5 t dry leaf/ha/year in Canterbury, New Zealand. Borens and Poppi (1990) reported that leaf dry matter digestibility ranged from 71 to 78% with a crude protein content of 21-24%. They suggested that the feeding value of tagasaste was similar to that of other conserved forages but less than that of intensively managed temperate pastures. During the establishment phase, young tagasaste seedlings are susceptible to browsing by livestock; Snook (1982) suggested that they should be protected from grazing for up to 3 years after sowing to allow proper development. During this time, inter-row areas could be cropped for grain or hay in an alley cropping system which could continue even after tree maturity.
Tagasaste has been used extensively in drier regions as a windbreak and shelter belt and also has some potential as a fuelwood species as the wood is fairly dense with a specific gravity of 0.7.
Also known as Desmodium gyroides, this species is an erect, much branched shrub to 2.5 m in height. Blue to purple papilionoid flowers are borne in dense racemes which produce typical Desmodium segmented pods.
It is native to Indonesia and is adapted to acid, infertile soils with high soluble aluminium content. It is more tolerant of waterlogging than L. leucocephala but its drought tolerance is not high although it will retain green leaf in the dry or cool season. It is resistant to fire.
Ahn et al. (1989) reported lower digestibility than L. leucocephala at around 55% with approximately 7% condensed tannins occurring in fresh leaves.
It is a relatively short-lived species and at Manado in Indonesia most plants died after 18 months. Jones (1984) reported that Codariocalyx was initially much more vigorous than L. leucocephala but its persistence was poor under a moderate cutting regime.
Although its palatability, intake and quality are often reported to be low (Keoghan 1987), it will grow on very difficult sites where there are very few other leguminous shrub options.
The species displays a range of morphology and habit from erect shrubs 2-3 m tall to prostrate herbaceous types less than 50 cm in height. Originally from Central and South America Desmanthus virgatus is now naturalised in many countries, including those in southeast Asia and the Pacific (Allen and Allen 1981). It belongs to the Mimosaceae family and is more tolerant of acid infertile soils than leucaena with a similar drought tolerance.
Little is known about its feeding value but it appears to be less palatable than leucaena (R.C. Gutteridge, unpublished data). However, it does not contain mimosine and therefore can be fed to non-ruminants without restrictions. Leaves contain 24-30% crude protein with an in vitro dry matter digestibility of 45-60% depending on stage of maturity. Kharat et al. (1980) found that the crude protein digestibility of D. virgatus was 58% while that for leucaena was 65%.
High yields from dense stands of D. virgatus have been obtained from a number of regions. Takahashi and Ripperton (1949) in Hawaii recorded yields of up to 23 t/ha total dry matter from four cuts per year. At the Kimberley Research Station in northwestern Australia, Parberry (1967) obtained whole plant dry matter yields of 35 t/ha/year. Desmanthus virgatus appears resistant to regular severe defoliation as there was no mortality in plants cut 5-7 cm above ground four times per year for 4 years (Takahashi and Ripperton 1949).
In the last 2-3 years D. virgatus has been widely promoted in Indonesia as an alternative to leucaena. In Queensland, the Department of Primary Industries is testing lines of D. virgatus for use in subtropical grazing systems particularly on heavy clay soils. Three cultivars, Marc, Bayamo and Uman, have recently been released.
Faidherbia albida is native to Africa and highly regarded by herdsmen and farmers in arid and semiarid regions from Senegal to the Sudan and south to the savannahs of Kenya, Tanzania and Zimbabwe (Wickens 1969). It is a thorny species and one of the largest forage trees, reaching a height at maturity of over 30 m with a canopy spread of up to 45 m. It is commonly found on flood plains and banks of large rivers on alluvial soil but it will grow on a wide range of soils including sand dunes and shallow rocky soils. Mature trees tolerate mild frosts and temperatures up to 44°C. Flowers are arranged in spikes 7.5-10 cm long. Pods are indehiscent and it is suggested (Lamprey 1967) that passage through an animal is necessary to stimulate germination.
Early growth rate is slow as the taproot establishes rapidly at the expense of top growth. On better sites, trees can reach 1.5 m in height in the first year. Although the tree is thorny, seedlings should be protected from grazing which can cause distortion of form.
Faidherbia albida is extremely important both for providing fodder to livestock and for enhancing soil fertility for crops. It retains its leaves through the dry season and sheds them just as the rainy season commences so that forage is available throughout the dry season when many other trees are leafless. This also means that it provides shade in the hottest time of the year. At the end of the dry season (the most crucial period of shortage of animal feed), protein-rich pods mature and fall from the tree in large quantities.
The leaf fall, root nodulation and continuous presence of livestock near the trees greatly enrich the soil by cycling the nutrients nitrogen, phosphorus and exchangeable calcium. This makes it an excellent agroforestry species as crops can be grown among scattered trees without shading during the wet season. Charreau and Vidal (1965) found that millet yields were 2.5 times greater and protein content of the grain 3- to 4-fold higher near the tree. Sorghum has been grown continuously for at least 30 years with F. albida without yield decline (Hocking 1987). However, a study by Vandenbeldt and Geiger (1991) indicated that improved soil fertility might precede the tree. They suggested that trees which survived and grew well had established on microsites of higher fertility.
The nutritional value of leaf is reported not to deteriorate on drying so that it is often fed dry in many parts of Africa (Hocking 1987). Boudet (1970) reported a crude protein content of 17.8% in dried F. albida leaf. Trees can produce an average of 135 kg pods/tree/year and a stand of 12 trees in the Sudan produced 200 kg crude protein from the pods alone (Wickens 1969).
In Niger, dry savannahs support about 10 cattle/km2 but this stocking rate can be doubled where F. albida trees are present (NAS 1979). An initial planting density of 10 x 10 m with thinning to wider spacings as the canopies closed was suggested. Typical densities in the Sahel, where the tree is most widely used, range from 10 to 50 trees/ha.
Although the tree is widely used throughout Africa, more research is required on the effects of protracted feeding of livestock with pods and leaf, techniques for better cultivation and propagation, and techniques for stimulating or increasing forage production.
Flemingia macrophylla is a member of the Fabaceae family. It is an erect woody shrub up to 3 m in height. Its leaves are trifoliate, relatively tough and papery. Flowers are borne in dense racemes with red blotches or stripes on a greenish-yellow background. Pods are small (11-15 mm long) and contain two shiny black seeds (Figure 2.7.2).
Flemingia macrophylla is native to Asia where it occurs in brushwood, forest margins, along waterways and in shaded locations. It is a hardy plant that can resist long dry periods but also tolerates some degree of waterlogging. In Indonesia, it has grown well on acid (pH 4-6) infertile soils with high soluble aluminium levels (80% saturation) (Budelman 1989).
Asare (1985) reported that F. macrophylla remained green throughout the year in Ghana and retained most of its leaf during the dry season making it suitable as a dry season browse species. Although the in vitro dry matter digestibility of leaf was less than 40%, palatability of young immature growth was adequate and much higher than that of older herbage. Asare (1985) found that crude protein levels in leaf varied from 14.5 to 18.3% depending on cutting frequency and height. A 14 week cutting frequency at 35 cm cutting height gave the highest leaf dry matter yields of 9.0 t/ha. Budelman (1989) reported leaf yields of 12.4 t/ha with four cuts per year at a plant density of 10,000 plants/ha. In southeast Queensland, Gutteridge (1990) found that F. macrophylla had a relatively high green leaf retention over the cool dry season with a mean leaf yield over 2 years of 125 g/plant.
Green manure and mulch
Because the leaf of F. macrophylla is relatively resistant to breakdown in soil, it has some potential for suppressing weeds in alley cropping and green manuring systems. Budelman (1989) found that 40% of a flemingia leaf mulch layer was still present after 7 weeks in comparison with only 20% of leucaena leaf. The mulch from F. macrophylla formed a solid layer that effectively prevented germination of weed seeds for 100 days. Yamoah et al. (1986a) showed that decomposition after 120 days was 96, 58 and 46% for Gliricidia sepium, F. macrophylla and Cassia siamea respectively. These data indicate that F. macrophylla may also be less digestible for livestock.
Flemingia macrophylla generally has lower levels of leaf nutrients than leucaena or gliricidia. Budelman (1989) reported concentrations of: N 2.352.83%, P 0.19-0.25%, K 0.98-1.40%, Ca 0.65% and Mg 0.20%. In alley cropping studies, maize yield from plots mulched with the leaf of F. macrophylla was lower than that mulched with leaf from either gliricidia or C. siamea but yields were similar when supplemental N was applied (Yamoah et al. 1986b). A mixture of F. macrophylla and leucaena or gliricidia may be an ideal alley cropping combination to provide a longer lasting mulch for weed control and soil moisture retention as well as more rapid release of nutrients.
Fig. 2.7.2. Leaf, flowers and pods of Flemingia macrophylla.
Although F. macrophylla does not produce a large woody biomass, Yamoah et al. (1986b) obtained 6.8 t dry stems/ha from a 2 year old stand indicating some potential for fuelwood production. In India, the plant is used as a host for the lac insect while hairs from the pods are used as a dye. It is also used as a shade and cover crop for coffee, sisal and cocoa
At least 44 species of Prosopis have been described and there is still much confusion over the taxonomy of the genus. Most species are native to the Americas ranging from the southwestern United States, through Mexico and Central America into South America as far south as Argentina.
At least three species, P. glandulosa, P. juliflora and P. ruscifolia, are aggressive woody weeds that cause major problems in grasslands. Prosopis glandulosa, the mesquite of southern USA, has reduced the livestock carrying capacity of over 30 million hectares of rangeland by competing with grasses for nutrients and water. These species spread rapidly due to their ease of propagation and ability to withstand adverse conditions and heavy grazing. They should never be introduced to new locations (NAS 1979).
Fortunately, other Prosopis species lack the aggressiveness of these weedy types but retain many of their desirable features. They are very drought tolerant and are adapted to the heat and poor soils of arid and semiarid regions. Most require at least 250 mm annual rainfall but some species have been found in areas receiving less than 100 mm.
Prosopis species are generally medium sized shrubs or short bunked, spreading trees. Most have spines and although spineless forms do exist they are generally less vigorous than the spiny types. Flowers are most often arranged in elongated spikes or spherical heads. Leaves are compound, bipinnate and feathery in appearance.
Usually found on poor land, Prosopis trees thrive on light sandy or rocky soils. Some species like P. pallida are remarkably salt tolerant and dominate arid, saline coastlines. Prosopis tamarugo is the only tree that survives on the arid salt flats of Chile's northern desert plateau where it produces the only available forage, timber and firewood (NAS 1979).
Prosopis pods are among the earliest leguminous foods known to have been used by man and are still a valuable source of carbohydrate and protein for many desert dwellers. Livestock also relish the pods which in many species contain a sweet, dry yellow pulp. The seeds in the pods are high in protein (34-39%) and the nutritious pods can sustain livestock in dry seasons when little other feed is available. However, when pods of some species (P. pallida and P. glandulosa) are fed as an exclusive diet for long periods, livestock, particularly cattle, can become malnourished and show ill-thrift symptoms. Thus, it is preferable that livestock consuming Prosopis pods should also have access to other feeds to balance their diet.
Several Prosopis species also provide edible foliage which can also be used as a livestock feed.
Perhaps the greatest use of Prosopis species is for fuelwood. The wood burns slowly, produces little ash and smoke and makes charcoal of very high quality. Many natural stands of Prosopis in South America have been virtually eliminated due to over-harvesting for fuelwood. Prosopis species are also used extensively for land reclamation, erosion control, windbreaks and shelter belts in inhospitable environments. In India, Douglas (1967) reported that a belt of Prosopis trees 3 km wide and 650 km long was planted to try to stop the advance of the Rajputana Desert.
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