| Nitrogen fixing trees for fodder production - A Field Manual |
R. T. Paterson, Joshua Daniel, G.R. Korwar, P.S. Pathak, M. De S. Liyanage, Mila G. Ejercito, Roland Lesseps, Soulivanh Novaho, Takashi Kate, A.S. Gill, James M. Roshetko and A.N.F. Perera
NFTs can be employed in many different fodder production systems in tropical areas of the world. The existing and potentially useful systems vary greatly from region to region. The degree of intensification of the systems is influenced by physical factors - soils; climate; species of domestic animals - together with socio-economic factors - human population pressure; availability of credit; and access to markets for both inputs and sale of products.
In this chapter, the principal tree fodder production systems are sub-divided according to their degree of intensification. Extensive systems are defined as those where the fodder trees are found either occurring, naturally or artificially established, at low densities. These trees are often in association with herbaceous pastures, annual crops or other woody species which may be used for non-fodder purposes such as production of fibre, fruit, fuelwood and timber. In these systems, the main objective of keeping animals may not be strictly commercial, since considerations such as food security, capital savings and social obligations may be of primary importance.
At the other extreme, intensive systems are those where attempts are made to maximize fodder production from relatively small areas of land, to optimize animal productivity within the inherent constraints of the chosen system. These production methodologies will normally be strictly commercial in nature and the animals will be managed in an attempt to maximize cash profit.
Small-scale farmers in developing countries normally access fodder resources from several of the systems to meet their fodder needs, farmers often develop hybrids of the fodder production systems mentioned here.
Scattered Trees In Pasture and Rangelands
The dry, tropical, deciduous forests and tropical thorn forests, under the influence of biotic and edaphic pressure, behave as savannas. Grazing animals in these systems are largely supported by the seasonal production of grasses growing under, or between the trees. Most of these ecosystems produce low levels of biomass production (0.5-1.0 t/ha/yr of dry matter DM). Many of these areas could be profitably converted into improved silvopastoral systems which would increase land productivity, reduce soil erosion and protect the lands from further environmental degradation. NFTs with fodder potential that could be used in such systems include species of Acacia, Albizia, Dichrostachys, Faidherbia, Hardwickia, Leucaena, and Prosopis.
In such improved systems, up to 650 trees/ha (commonly 100-400 trees/ha) could be planted in rows, either as mixtures or as single species. Spacing would vary with tree species, but would normally range from 4 x 4 to 6 x 6 m, or wider. Regular tree distribution provides uniform shade to rangeland. Uniform shade reduces excessive soil temperatures, prolongs the succulent phase of understory grasses and legumes and furnishes livestock a pleasant more productive environment.
The age at first harvest will vary with soil, climate and the tree species. Cutting should be delayed until the trees have grown beyond the reach of the grazing animals, to prevent direct browsing. Under dry conditions, the first harvest from fast growing trees might be delayed until 2-3 years after establishment. For Hardwickia binata, prunring and thinning during a 5-year establishment period results in accelerated growth. Fodder harvest should start after the establishment phase.
The tree foliage should only be used during periods of fodder shortage - i.e. the dry seasons. Migratory grazers usually lop trees only once per year, while settled agro-pastoralists may lop twice. The survival of a number of short duration species is favored by lopping only once per year, although species such as Leucaena leucocephala and Sesbania sesban may be cut two or more times per year. With most deciduous species, a flush of growth of leaves and flowers takes place during the summer months. Cutting is delayed until the dry season when other sources of feed are scarce. The foliage should be cut before the leaves start to fall, in order to prevent loss of feed quantity and quality. Cutting regimes should be determined through testing under local conditions.
Trees should be lopped at a minimum height of 2 meters without removing more than two thirds (67%) of the foliage at any one time. However, in practice, it is common for more than 90% of the leaves to be harvested, even though this is known to reduce subsequent growth and survival of the trees. In many studies, species of Acacia, Albizia, Hardwickia and Leucaena produce maximum annual yields under cutting regimes that remove only 30-60% of the foliage at each lopping.
In most pastoral situations, the lopped branches are allowed to fall under the tree for consumption by livestock. This often results in maximum utilization of the available fodder, as leaves, pods and tender twigs will all be consumed. Where the fodder is removed for feeding to animals in confinement, usually only the leaves are taken from the field. While this may reduce the amount of available feed, the wilting associated with the delay in feeding may increase animal intake of those species which contain volatile anti-nutritive factors (e.g. Gliricidia septum). Alternatively, there are suggestions that wilting will decrease the digestibility and voluntary intake of foliage of trees such as Calliandra calothyrsus.
Lopping produces not only leaves and pods for fodder, but also branches and sterns for firewood, fence construction or other uses. The ratio of edible to non-edible material (E/NE), fodder to total biomass, is therefore an important variable to be considered in the selection of species. The actual ratio in any given situation will depend, to some extent, on the tree management regime used and on the animals to which the fodder is fed. But many species display clear differences in their foliage to woody biomass ratio. Representative production levels and E/NE ratios for a range of mature NFTs (age 8-9 years) under silvopastoral systems are shown in Table 1.
Scattered Trees In Croplands
Fodder trees are commonly found growing in tropical croplands. They may be either planted by the farmer, or be left in place when the land is cleared from woodland or forest. Whatever their origin, they may be pollarded, coppiced or lopped for fodder. There is no fixed density or planting pattern for these trees, often the population is low (50-100 trees/ha), and the arrangement is random. Generally, to minimize competition with the accompanying crop, the species chosen for this purpose should have a sparse canopy. For those species which produce a dense canopy, lopping is scheduled to decrease competition. Foliage resulting from such loppings be used as fodder or left in the field as green manure for crops. The remaining foliage is usually reserved for the dry season after the harvest of the crop. Foliage may be left in the field for consumption or carried to animals in confinement. In either case, the tree fodder is usually mixed with crop residues to improve the utilization of this poor quality roughage.
NFTs grown in this type of fodder production system include Acacia nilotica, Albizia lebbeck, Alnus nepalensis, Dalbergia sissoo, Erythrina variegata, Faidherbia albida, Gliricidia septum, Pongamia pinnate, Prosopis cineraria, Sesbania grandiflora and S. sesban. The choice of species is governed to a large extent by the degree of competition that it will present to the crop during the main growing season. For example, F. albida is an ideal species because it tends to shed its leaves during the wet season and therefore presents minimum competition to the crop. By contrast, A. nilotica can produce a dense canopy and provide serious competition for moisture. Caution should be used when introducing this species to new areas, particularly semi-arid regions. It is important to recognize that a species valuable for one site may be problematic at others.
In addition to producing fodder, this type of system may improve crop production. During the non-cropping season, animals feeding in the fields contribute to soil fertility through their droppings. Crop residues left in the field also recycle nutrients to the soil. Tree shade decreases soil desiccation and offers a pleasant and more productive environment for animals and farm workers. The presence of trees can reduce wind speed, which in turn will reduce soil desiccation and erosion. The consequent improvements in soil physical and chemical properties can result in higher crop yields under trees than in similar areas without tree cover.
The potential of NFTs as fodder species in linear plantings has been widely accepted in the tropics. Common forms of these planting patterns are discussed below, and a list of species suitable for each purpose is given in Table 2.
Farm and Field Boundaries. Tree species are often planted along the perimeter of the farm or field boundaries for demarcation and to provide a range of products including fruit, timber, fuelwood and fodder. Species are often chosen for their ability to grow erect, and to resist repeated defoliation by pruning or lopping. They should provide minimal competition with the companion crops for moisture, nutrients and light, and should not be allelopathic.
Windbreaks. To protect arable crops from high velocity winds and wind erosion, trees are commonly planted adjacent to fields. These windbreaks may be single or multi-rows. In multi-row windbreaks, tall species are flanked by shorter species. The purpose of windbreaks is to slow the wind, not stop it. If the barrier becomes too dense, strong winds can cause crop damage behind the windbreaks. It is therefore necessary to prune and thin the trees at regular intervals to maintain a semi-permeable barrier. This ensures the regular availability of wood products, as well as high-quality animal fodder. Encroachment by advancing sands from deserts or coastal dunes can be controlled by rows of trees, called shelterbelts. Depending on species selection, shelterbelts may also provide fodder.
Live Fencing. Conventional barbed-wire fencing with metal or wooden posts is often too expensive for small-scale farmers. Live fence posts are an alternative many farmers use to reduce the high costs of fencing materials. Further savings can be made by using impenetrable live hedges of NFT species to replace other purchased inputs. In either case, the prunings from live fencing can provide nutritious fodder for livestock. Species chosen as live fencing should be easy to establish, preferably by vegetative means, should have a deep root system and should not compete strongly with the adjacent crop for moisture and nutrients. They must withstand repeated pruning and lopping at a constant height of 1.5-2.0 m. Gliricidia septum and Erythrina spp. are commonly employed for living posts. These species, as well as Acacia angustissima, Calliandra spp., Desmodium spp. and Sesbania sesban, make effective hedges.
Along Roads, Railways and Canals. NFTs are planted along roads, railways and canals to provide shade for people and animals, as well as to decrease evaporation from soil and water. Species for these niches must be chosen with care. In general, erect shade and timber trees are best. Fodder may be a secondary product from these trees. It is also possible to include fodder trees in the mix of species.
Natural Woodlands and Forests
Woodlands and forests often contain many NFTs of significant fodder value. Side branches and pods of these trees may be periodically harvested for livestock feed. Fallen litter and pods may either be browsed in place, or gathered and carried to livestock. An advantage of the latter method is that the material can be stored for use in times of feed shortage.
The harvesting of fodder from these public lands is often unregulated. Where fallen leaves and pods are gathered for removal, the only damage is the loss of nutrient inputs to the soil. On the other hand, uncontrolled lopping frequently results in over-utilisation of the most productive and nutritious tree species. This is undesirable, because less useful species will grow unhindered under reduced competition. In time, these less useful species will dominate the site, leading to reduced vigour and poor regeneration of the preferred fodder species. Under extreme conditions, the preferred species will eventually die out. Only through education of local users and careful management can the degeneration of these forests be prevented.
In general, establishment and thinning in these natural forests occur without human intervention. Thus, there are no recommended tree spacings and densities. Similarly, there are no general management regimes for age at first harvest, frequency of cutting and intensity of utilization. Management regimes must be based site characteristics. Moderate use and protection are key to long-term sustainable production. Supplemental tree planting, protection of natural regeneration and the removal of undesired species will improve the species mix and fodder production of this system.
Examples of woodland and forest genera that produce significant quantities of edible leaves include Acacia, Albizia, Dichrostachyus, Erythrina and Prosopis. With some species, the pods are a more important fodder resource than the leaves. These include Acacia plenifrons, Albizia saman, Enterolobium cyclocarpum, Faidherbia albida and Prosopis juliflora.
While regeneration programs are often initiated for purposes that have little to do with animal production, livestock can be direct beneficiaries of such activities where suitable fodder species are present, or included in the mixture to be planted. Important considerations include protection and encouragement of natural vegetation; natural regeneration and enrichment planting of NFTs; nurse cropping with NFTs; and silvopastoral systems. In many cases, at the conclusion of the renovation phase, the regenerated land will be used under one of the categories discussed above.
In the selection of NFT species for revegetation, emphasis must be given to the ability to establish and survive in difficult, deteriorated habitats. Many species have been tried on rocky, gravelly and generally degraded lands. Those that have survived best under the most harsh conditions in India include Acacia tortilis, Albizia amara, and Hardwickia binata. Some typical planting arrangements and production levels are shown in Table 3.
A number of points need to be considered concerning successful restoration of degraded habitats. The watershed approach should be used, since measures taken on a particular area can be destroyed or negated by neglect further up the slope. Contour trenches are effective in reducing run-off and conserving both soil moisture and nutrients. Cover crops of Stylosanthes hamata, Leucaena leucocephala and similar fast-growing species can be employed to colonise and enrich the exposed soil sub-strata. These plants will decrease erosion and provide high quality fodder, while encouraging better growth from companion plants. To allow good plant establishment, it is important that animals be excluded from the area for a period of at least 3-4 years. This can be achieved through the use of fences and trenches, but must also include community involvement and cooperation. The land will not be useless to the community during this critical establishment period. Fodder from the herbaceous cover-crop species can be periodically harvested for removal and feeding to livestock.
The natural regeneration on the site should be managed to maximize the production of useful biomass. Undesirable species should be removed, and useful species should be pruned for desirable form. Management can also be used to reduce shading and promote beneficial grasses and herbaceous legumes. While pruning and thinning may take place after 2-3 years, lopping of the regenerated species should not take place until year five.
Fodder Trees with Plantation Crops
Plantation crops play a vital role in the economy of developing countries in the humid tropics. The integration of these systems with livestock farming has been a productive and profitable practice of sustainable landuse. Coconut (Cocos nucifera), oil palm (Elaeis guineensis) and rubber (Hevea braziliensis) have great potential for the interplanting of fodder trees. Among nitrogen fixing fodder trees, Calliandra, Gliricidia and Leucaena are compatible with plantation crops. These fodder trees are commonly grown as hedges along boundaries or in the avenues between the rows of the plantation.
By virtue of the wide spacing adopted in coconut plantations, almost 70% of the land could be utilized for the intensive cultivation of companion species. Recent studies have demonstrated that NFT hedgerows can be successfully grown at spacings of 4 x 0.5 m in young plantations with coconut trees spaced 10 x 5 m apart. In mature coconut and oil palm plantations, where 7 x 7 or 9 x 9 m spacing is common, the fodder species may be grown in double rows spaced 2 x 1 m apart, giving a density of 2,400 trees/ha. In contrast, there are less opportunities for fodder tree production in rubber plantations because of the narrow 5 x 5 m spacings. NFTs can be grown only during the pre-tapping period. After this period, usually about 6 years, the plantation canopy will close preventing further understory cultivation.
To maximize fodder production, the NFT hedge should be allowed to grow for one year before the first harvest. Thereafter, the hedge can be pruned 3 4 times per year at a height of 100 cm. The foliar material can be used directly for feeding livestock, particularly during the dry season when the high protein content of the foliage can supplement low quality roughage from crop residues. Where animals are not an integral part of the production system, the foliage can be used as green manure to restore soil fertility to both degraded lands and plantation areas. Coffee (Coffea arabica and C. robusta), cacao (Theobroma cacao) and tea (Camellia sinensis) are plantation crops often grown with an overstory of nitrogen fixing shade trees. Trees are spaced from 3 x 3 to 12 x 12 m throughout the plantation and periodically pruned to maintain the desired level of shade. Most of the biomass removed during pruning remains in the plantation as green manure. However, when fodder species are employed as shade trees, some of this material can be used as livestock feed. Commonly used, dual purpose shade/fodder species include Albizia chinensis, A. odoratissima, A. procera, Gliricidia sepium, Erythrina poeptugiana, E. subumbrans and E. variegate. Albizia saman and Paraserianthes falcataria have also been used for these purposes.
Alley cropping was originally developed as a diversified, sustainable farming technique to combine soil conservation with crop production. Annual or permanent crops are grown in alleys between dense single or double hedgerows of NFTs. Distance between double-rows is 50 cm. Spacing within the row varies from 5-50 cm. Between hedgerows spacing is 1-5 m. To limit competition for light, hedgerows are pruned periodically to a height of 40-100 cm. The leafy prunings are applied to the soil in order to recycle nutrients to the crop. Woody material is used as fuelwood, poles or other purposes. Leafy prunings harvested during the last weeks of crop growth or in the dry-season can be removed for use as animal fodder. Alternatively, during the non-cropping season, animals can graze directly on hedgerows and the crop residues. In either case, the nutrient loss from the system is minimal if the animal manure is returned to the field as fertilizer for the subsequent crop. Where animals are a notable component, this system is usually referred to as alley farming, rather than alley cropping.
Sloping Agricultural Land Technology (SALT) is a form of alley cropping where the primary aim is to control erosion on steeply sloping land, while producing crops for sale and subsistence. Hedgerows of NFTs are planted on the contours at spacings of 1 to 5 meters. Pruned periodically, hedgerows provide green manure for crops and fodder for livestock. Woody material from the prunings is often laid on the ground at the base of the trees to provide a further physical barrier against erosion. Some of the woody material can be used or sold as fuelwood. Permanent crops such as coffee, citrus and cacao are planted on the farm for income generation and home use. The land not occupied by hedgerows, or permanent crops, is planted to subsistence crops such as maize, sweet potatoes, pineapples, peanuts and mung beans.
The choice of NFT species for use in alley farming is of paramount importance. The ideal species would: establish easily; grow rapidly; remain productive under repeated harvest; show excellent fodder and green manure characteristics; have a deep root system that was non-competitive with crops; tolerate environmental extremes (drought, water logging, soil acidity); have a high edible to non-edible material ratio; have small leaflets which were retained in the dry season; and be free from pests and diseases. Species commonly used in alley farming include Calliandra calothyrsus, Desmodiun rensonii, Flemingia macrophylla, Gliricidia septum and Leucaena leucocephala. Sesbania sesban is also commonly used in alley farming systems. However, under repeated heavy harvesting S. sesban mortality may increase and plant longevity decrease. To prolong survival of this species 10 to 25% of the foliage should be retained after each harvest.
Fodder Banks or Reserves
In areas with a long dry season, it is advantageous to reserve an area of fodder specifically for use in times of feed scarcity. The objective of such reserves is to maximize fodder production from a small area. Thus, reserves are commonly fertilized with farmyard manure or inorganic fertilizers in accordance with local recommendations. Indeed, it is of great importance to return the manure to the reserve, in order to avoid rapid depletion of soil fertility and reduction of fodder yield. Reserves can be composed of pure grasses (energy bank), of pure legumes (protein bank), or of a combination of grasses and legumes (protein-energy bank). As a sole feed, the energy bank provides only a maintenance ration to ensure animal survival during the dry season. The protein bank is a high-quality feed used to supplement low-quality feeds (crop residues, dry season grasses, etc.) to provide a production ration. The protein-energy bank is designed to provide a complete diet which is balanced in terms of both digestible protein and energy.
To maximize fodder production trees should be planted at close spacings. In protein banks in-row spacing of NFTs ranges from 5-50 cm. Between row spacings of 50-150 cm are common, although if the area is to be directly grazed, wider walk-ways are necessary every fourth or fifth row to allow animals access to the entire bank.
Protein-energy banks are usually managed under a cut-and-carry system. NFTs are usually associated with Napier grass (Pennisetum purpureum), or at altitudes over about 1,800 m, with Guatemala grass (Tripsacum laxum). Guinea grass (Panicum maximum) is more persistent and appropriate if the bank is to be managed under grazing. In the Caribbean, it is common to plant alternate rows of grass and NFTs, or one row of trees to two rows of grass. In India, double rows of each component give the best results. In Kenya, with a bimodal rainfall pattern, highest yields of both biomass and crude protein are achieved with one row of trees to three or four rows of grass. The most productive tree-to-grass ratio must be determined for each region. Between row spacings in protein-energy banks is usually 100 cm.
Establishment should take place at the beginning of the rains. It is often best to plant tree seedlings, in order to reduce competition from the fast-growing grass. After three months, when grass has reached a height of 120-150 cm, it should be cut to a height of 10 cm. The first harvest of NFTs should be delayed until they have reached a minimum height of 180 cm, after about 6-8 months for most sites. NFTs should be cut to a height of 60 80 cm.
Since the banks are intended only for dry season use, impose routine management at the end of the growing season - the second growing season where rainfall is bimodal. Banks should be rotationally grazed or cut at intervals of eight to ten weeks during the dry season. At the start of the rains, the whole area should be cut back to the heights noted above. Under management that avoids over-utilization, banks should remain productive for at least eight years, at which time it may be necessary to replant the grass component to ensure continued high levels of production. The useful life of the tree component should exceed 20 years.
Animal production will vary widely, depending upon the type of bank, soil fertility, fertilizer regime applied, and climate. Without irrigation, where annual rainfall is in excess of 1,000 mm and with the farmyard manure returned to the soil, annual yields from commercial scale protein banks of 10 t/ha of leaf DM (with about 25% crude protein) have been obtained. With protein-energy banks yields of 15 t/ha of DM from the grass (7% crude protein) and 5 t/ha leaf DM from the NFTs (25% crude protein) are possible.
Intensive Feed Gardens
Unlike fodder banks, intensive feed gardens (IFGs) are designed to provide feed throughout the year. However, the objectives of these two systems are identical, i.e., to maximize fodder production from a small area. Like protein-energy banks, IFGs contain both grasses and NFTs and are intended to provide a complete diet balanced in terms of digestible protein and energy. IFGs are designed to allow small-scale farmers to maximize animal production when agricultural land and feed resources are limited. This system is appropriate for the semi-arid to humid tropics, and provides excellent erosion control on sloping land.
The proportion of the IFG devoted to tree and grass components varies by site and management objectives. Approximately half the garden should be established in NFTs and half in grass. Grass and NFTs should be arranged in adjacent double-rows across the garden. In-row spacing of NFTs should be 5-50 cm and the distance between double-rows is 50 cm. In-row spacing of grasses should be 35-40 cm and the distance between double-rows is also 50 cm. Distance between rows of grasses and NFTs should be 75-100 cm. Wide access rows for livestock are not necessary because gardens are managed by the "cut-and-carry" method. Grazing should not be allowed. The arrangement described here, while generally suitable, should be altered to meet the needs of each situation.
IFGs should be established at the beginning of the rainy season. NFTs should be established by direct sowing or transplanting seedlings 4-6 weeks before grass. This will minimize competition between components during the critical establishment period. During this period, all invasive weeds should be removed. Grasses can be harvested 6-8 weeks after planting, and thereafter every 4-6 weeks. Cutting height for grasses is 15 cm. NFTs are not cut before they attain a height of 180-200 cm, approximately 812 months after planting. Thereafter NFTs can be harvested every 8-12 weeks at a height of 100 cm. To maintain soil moisture and fertility, 50-70% of the NFT biomass harvested should be applied to the garden as green manure. Farmyard manure or organic fertilizers should also be applied according to local recommendations.
An IFG of 200 mÃ½ meets the feed needs of 5-6 goats, a 400 mÃ½ garden should feed one cow. Because IFGs are utilized year-round, plant longevity is less than in fodder banks. When biomass yields decrease, grass and NFTs should be replanted. Appropriate grass species for this system include Napier (Pennisetum purpureum), Guinea (Panicum maximum), Para (Bracharia mutica) and African Star (Cynodon plectostachus). Appropriate NFTs are Acacia angustissima, Cajanus cajan, Calliandra calothyrsus, Desmodium rensonii, Flemingia macrophylla, Gliricidia septum and Leucaena leucocehephala.