INTRODUCTION
Multipurpose trees play a critical role in the intensive integrated farming system based on sugar cane and developed by CIPAV (Preston and Murgueitio, 1992; Figure 1) in close cooperation with local farmers in the Cauca valley in Colombia. This system recognises that renewable biomass is the only sustainable source of fuel, feed and food, and that additionally it can be a medium for reversing environmental degradation.
The system is based on sugarcane which provides the carbohydrate feed (the juice and tops) and also fuel (the bagasse). Multi-purpose trees and water plants supply the protein and the trees play other important roles such as controlling erosion, providing sinks for carbon dioxide (the standing biomass) and methane (at the interface between the decaying fallen leaves and the soil) and as a source of biodiversity. Sugar cane and trees have well developed systems of biological pest control, require minimum synthetic chemical inputs and are easily separated into high and low fibre fractions as required for the different end uses of feed for monogastric and ruminant animals and fuel.
The trees which have had most farmer impact are Gliricidia sepium, Trichantera gigantea, Erythrina glauca and edulis. The foliage from Trichantera gigantea is consumed by pigs; that from the other trees is more appropriate for ruminants.
The preferred animal species are pigs and ducks which adapt readily to the “non-conventional” high-moisture feed resources (cane juice, tree leaves and water plants) and have a high meat: methane production ratio. They are complemented by African hair sheep which derive most of their feed from the cane tops and tree foliage. Buffaloes and/or triple purpose cattle supply draught power as well as meat and milk. All the livestock are managed in partial or total confinement to minimize environmental damage and to maximise nutrient recycling to the crops.
The CIPAV model is flexible as witnessed by the increasing acceptance of many of the elements in the model by both resource-poor and entrepreneurial farmers.
FIGURE 1. The CIPAV Farming System.
THE ROLE OF MULTI-PURPOSE TREES
The role of multipurpose trees in this mixed farming system is as:
Monogastric animals
When monogastric animals are fed basal diets derived from tropical feed resources such as sugar cane, cassava, bananas, sweet potatoes or oil palm, the supplementary nutrients that are needed are protein, lipids, minerals and vitamins. The usefulness of tree foliages for these species will therefore be a function of their capacity to supply some or all of these nutrients.
The total protein needs of monogastric animals are reduced considerably when low-protein basal diets are fed. This is because the ratio of essential (EAA) to non-essential amino acids in protein supplements such as oilseed meals and tree foliages is close to the optimum. In contrast, when cereal grains are the basis of the diet, there is an inevitable over-supply of non-essential amino acids, and total protein supply must be higher in order to provide the required amounts of EAA.
The new approach to assessing the suitability of a protein supplement for a basic diet low in protein, is to calculate the ratios of each essential amino acid as a function of the amount of lysine, and to compare this with the optimum determined from studies with synthetic amino acids (Wang and Fuller, 1989). On this basis, the aquatic plant Azolla filiculoides has an excellent balance of amino acids (Figure 2).
FIGURE 2. Amino acids in Azolla: comparison with optimum
For ruminant animals, the need is for trees with high production of biomass and high content of protein in a form that will escape the rumen fermentation. Thus the presence of moderate concentrations of tannins could be important as a means of ‘insolubilizing’ the protein. If the desired tree species is low in tannins, then another approach is to mix with it a species which has a high content of these substances. In order to achieve acceptable intake, tree forage is normally limited to 30% of the diet DM. High digestibility, good balance of essential amino acids and minerals and vitamins are also required from the forage.
Six species are presently being used in ruminant diets. They are:
The choice of a particular tree will be decided by climatic and soil considerations. Thus Erythrina glauca is specifically adapted to acid soils with a high water table, and a propensity to flooding. Acacia mangium is especially tolerant of acid soils saturated with aluminium. Leucaena leucocephala is not normally used as it is least tolerant of all the species to acid soils. Where leucaena can be grown, it is outyielded by gliricidia, which is also more resistant to insect attack and is more easily harvested. The latter is important in “cut and carry” systems which is the usual practice on small farms.
GLIRICIDIA SEPIUM
The traditional way of establishing Gliricidia as a ‘live’ fence is by planting a stake in the ground. However, when the aim is to produce forage for intensive harvesting it is essential to develop it from seed. Survival of trees established from seed is much higher than when stakes are used (Figure 3). Production of biomass is higher when Gliricidia is established from seed (Figure 4). Biomass yields of Gliricidia are consistently high, especially when established at high plant densities. However, in practice, with only 50 cm between rows, harvesting is made difficult and present recommendations are to plant at 1 m between rows and 50 cm between plants.
It seems that the origin of Gliricidia sepium is in Guatemala. Certainly, there are differences among provenances according to where the seed was collected. The provenances from Guatemala and from Colombia seem to be the highest producers in the series of trials carried out in Colombia, using seed collected and provided by the Oxford Forestry Institute, UK (Figure 5).
FIGURE 3. Effect of plant density of method of establishment on survival of Gliricidia sepium
FIGURE 4. Effect of plant density of method of establishment on survival of Gliricidia sepium
FIGURE 5. Edible forage yield of six provenances of Gliricida sepium (total of 10 cuts at 3 month intervals).
The height above ground level at which Gliricidia is harvested has little effect on biomass yield. However, it has been observed that cutting at about 1.2 m gives better weed control and is also more convenient for the person doing the harvesting (Figure 6). There are two ways of harvesting the foliage from Gliricidia. One is by cutting the branches with a knife or machete; the other is to strip by hand the leaves and petioles from the stems. The former is recommended as it stimulates the appearance of more buds which in turn results in a higher biomass yield (Figure 7).
FIGURE 6. Effect of cutting height on forage yield of Gliricidia sepium.
Source: El Hatlco (unpublished)
FIGURE 7. Effect of harvesting method (cutting vs. stripping) on forage yield of Gliricidia sepium.
Source: El Hatloo (unpublished)
Nutritive value
Foliages from multi-purpose trees play a dual role in ruminant feeding. They help to provide an improved ecosystem in the rumen, which is reflected in increased microbial activity which in turn leads to an increased rate of digestion of the fibrous basal diet. In certain cases, especially when tannins are present in moderate amounts, the protein in the leaves may partially escape the rumen fermentation and contribute amino acids directly at the level of the intestine.
Gliricidia foliage appears to provide bypass protein since there is a marked stimulation of growth rate when it is fed as a supplement to a basal diet of low digestibility, in this case King grass harvested during the dry season. In the experiment shown in Figure 8, growth rate of recently weaned calves responded to Gliricidia levels in the diet equivalent to 5% of liveweight.
FIGURE 8. Growing steers on a King grass diet supplemented with Gliricidia foliage.
Gliricidia has proved to be an excellent supplement to a basal diet of sugar cane tops for African hair sheep managed in total confinement (Table 1). Levels of performance of the sheep fed cane tops, Gliricidia foliage and a mixture of poultry litter and rice polishings (9:1) together with urea-molasses blocks have been highly satisfactory (Table 2).
| Diet components | Fresh basis (kg/d) | Dry basis (%) |
|---|---|---|
| Gliricidia | 0.777 | 9.3 |
| Sugarcane tops | 5.640 | 72.4 |
| Multinutrient block | 0.121 | 6.2 |
| Poultry litter | 0.204 | 10.6 |
| Rice polishings | 0.021 | 1.0 |
| Total dry matter* (kg/d): | 1.735 | |
| (proportion of live weight): | (0.045) |
* For a sheep unit (1 ewe of 25 kg and 1 lamb of 14 kg)Source: Mejía et al. 1991.
| Mean | Standard deviation | n | |
|---|---|---|---|
| Live weight (kg) | |||
| Birth | 2.32 | 0.52 | 167 |
| Weaning | 14.90 | 2.62 | 84 |
| Weight gain to weaning (g/d) | 106 | 33.6 | 84 |
| Age at weaning (days) | 129 | 45.5 | 84 |
| Lambing interval (days) | 284 | 85.3 | 44 |
| Litter size* | 1.16 | 44 | |
| Lambs per ewe per year** | 1.49 | 44 | |
| Mortality (% of all births) | |||
| Perinatal | 5.5 | ||
| Birth to weaning | 10.4 |
* Number of lambs born per parturition
** Mean number of lambs born per ewe per yearSource: Mejía et al. (1991)
It is sometimes reported that Gliricidia is not very palatable even to ruminants because of the presence of secondary plant compounds. In this trial with sheep, admittedly accustomed to previously to consuming Gliricidia, it was selected in preference to all the other feeds including Leucaena.
FIGURE 9.
Diet preference by sheep. (Cafeteria trial; 3 groups; 21 days).
Source: Mejia et al. 1991
ERYTHRINA POEPPIGIANA
Goats fed a basal diet of King grass and reject banana fruit responded with linear increases in milk production when offered increasing levels of foliage of Erythrina poeppigiana (Figure 10).
FIGURE 10. Milk production of goats fed King grass. Effect of giving Erythrina tree foliage.
TRICHANTERA GIGANTEA
This tree is native to the Andean foothills in Colombia. It is not a legume but its vigorous regrowth even with repeated cutting and without fertilizer applications indicates that nitrogen fixation occurs in the root zone either through the action of mycorrhiza or other organisms. Nacedero (Trichantera gigantea) responds in a similar way to height at cutting. The yield is slightly higher when it is harvested at about 1-1.2 m above ground level (Figure 11).
The advantage of this tree is that the leaves are consumed quite readily by pigs. Results from replacing 75 % of the soyabean meal in cane juice diets for pregnant sows have been very encouraging (Figure 12). Results with growing pigs have been less satisfactory. Performance was reduced at all levels of substitution of soyabean meal by Trichantera (Figure 13).
FIGURE 11. Cutting height and biomass (edible forage) yield of Trichantera gigantea.
CHEMICAL TREATMENT OF TREE FOLIAGE
There are interesting possibilities for improving the digestibility of tree foliages by simple methods of chemical treatment. Ensiling with acetic acid has given promising results when applied to the foliage of Trichantera (Figure 14).
Ensiling can be used to neutralize other secondary plant compunds, as in this case the cyanogenic glucosides in the leaves of cassava (Table 3).
The treatment of tree foliage to improve their nutritive value, to remove secondary plant compounds and to enable the longer term storage of feed material is now a high priority for future research.
FIGURE 12. Foliage of Trichantera gigantea as replacement for soyabean meal in cane juice diets for pregnant sows.
FIGURE 13. Foliage from Nacedero (Trichantera gigantea) as replacement for soyabean meal in growing pig rations.
FIGURE 14. Effect of acetic acid and sodium hydroxide on degradability of Trichantera gigantea (in situ rumen nylon bags).
| HCN content (mg/kg DM) | |
|---|---|
| Fresh cassava leaves | 863 |
| Cassava silage | 33 |
| After sun-drying for 4 hours | 261 |
| Sun-drying 4 hours then ensiling | 32 |
| After drying 2 days in shade | 274 |
| Drying 2 days in shade then ensiling | 34 |
| Dried cassava leaf meal | 80 |
Source: Chinh et al. (1991).
CONCLUSIONS
Multi-purpose trees play an important role in an integrated system based on sugarcane, developed in Colombia. They provide feed for pigs, ducks and small ruminants (sheep and goats). Buffalo and triple purpose cattle are preferred to single-purpose beef or dairy cows. The use of renewable biomass also supplies a sustainable source of fuel and reverses environmental degradation.
The species include the legumes Gliricidia sepium, Erythrina poeppigiana, E. glauca and E. edulis, and Trichantera gigantea (family: Acanthaceae).
Plant survival and biomass production were highest when Gliricidia was established from seed, planted at 50 cm spacing with 1 m between rows. A number of provenances have been tested, of which the seed from Guatemala and Colombia were most productive. Cutting at a height of 1.2 m is recommended as the method of harvesting.
Gliricidia provides bypass protein for ruminants and is fed as a supplement to low-digestibility basal feeds (King grass and cane tops). Contrary to reports elsewhere, there were no problems of acceptability of Gliricidia to animals and sheep showed preference for this feed in a cafeteria trial. Good animal performance has been obtained with cattle and sheep.
Similarly, milk production of goats responded to the inclusion of Erythrina foliage in a diet of King grass and bananas.
Trichantera gigantea is a new candidate for inclusion in integrated systems and grows well with repeated cutting and without fertilizer input. Its particular value is as a protein supplement for monogastrics (pigs) and it has replaced up to 75% of soyabean meal in pregnant sow diets.
A future priority is the treatment of tree foliage to improve the nutritive value and remove secondary plant compounds.
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