Leucaena in Eritrea A g u i d e to e s t a b l i s h m e nt a n d m a n a g e m e nt
Authors Mr Eskender Tesfay, Forage Research Scientist, Animal Feed & Feeding Unit, Livestock Research Division, NARI. Mr Zerai Sultan, Forestry Research Unit (Agroforestry), Natural Resources Management Division, NARI. Dr Bruce Cook, formerly Principal Scientist (Tropical Forage Systems), Department of Primary Industries and Fisheries, Queensland, Australia. Acknowledgements The authors acknowledge the following sources of information and some of the images used in this publication: Dalzell, S., Shelton, M., Mullen, B., Larsen, P. and McLaughlin, K. (2006). Leucaena A guide to establishment and management. Partridge, I.J. (Ed), Meat and Livestock Australia Limited ISBN: 1 7419 1013 7 Winrock (1985). Leucaena, wood production and use. Winrock International, 38 Winrock Drive, Morrilton, Arkansas 72110-9370, USA. We also acknowledge the Australian Government, Department of Agriculture, Fisheries and Forestry, who funded the development of this booklet under the Forage Options Project, and thank Dr Alan Robertson for sharing his experience on aspects of leucaena propagation and management. Acknowledgements Leucaena makes an effective windbreak protecting other crops, such as bananas, around Tesseney.
Foreword ii This technical manual is the result of five years of intensive collaborative research work supported by the Australian Government and jointly carried out by researchers from Animal Feed and Feeding Unit of the Livestock Research Division within the National Agricultural Research Institute (NARI) in Eritrea and Australian lead agencies. The research was initiated under the project title, Forage Options for Livestock in Eritrea, to conduct observation and evaluation trials of a large range of herbaceous legumes, grasses and fodder tree genotypes at different agro-ecological zones of the country. Indeed over 600 accessions of grasses and legumes selected from around the world were tested and a number of forages with excellent potential for application in the various farming systems in Eritrea were identified. The legume shrub, leucaena, was outstanding among these elite varieties. The manual, Leucaena in Eritrea: a guide to establishment and management, combines the results of this research with relevant information from other countries having similar agro-ecological conditions to those in our country, and where leucaena has proven a valuable component of livestock feeding systems. The manual is designed with the intention to support zoba extension staff in promoting the use of leucaena in Eritrea. I would like to stress that this is not a comprehensive manual for leucaena in our many farming systems. As Eritrea has diverse agro-ecological zones and edaphic characteristics, our advice to extension staff is to continue conducting trials at the local level with farmers to identify if leucaena and other forages with high production potential have application in their specific farming systems, and to develop best management practice for the best adapted in those systems. It is my hope that the extension agents will make the best use of this manual for forage development in their respective places. Iyassu Ghebretatios DG-NARI
Contents iii Summary Benefits of leucaena Things to consider v v Introduction 1 What is leucaena? 1 Where does leucaena come from? 1 Why plant leucaena? 1 Establishing leucaena 1 Where does leucaena grow best? 1 Cultivar selection 2 Seed treatment 3 Sowing and planting 4 Weed control 9 Companion grasses 9 Managing established leucaena 9 Soil fertility maintenance 9 Pests and diseases 9 Cutting or grazing management 10 Irrigating leucaena 12 Leucaena as a livestock feed 13 Leucaena seed production 14 Soil conservation 14
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Summary Benefits of leucaena Leucaena is a multi-purpose tree (MPT): livestock feed windbreak fuel wood construction soil fertility improvement forage for bees from flowers. Animals prefer leucaena to most other forages, resulting in high intake and weight gains. Leucaena leaf is high in protein and is easily digested by ruminants (similar feed value to alfalfa). Leucaena produces high-quality green leaf well into the dry season. It has the potential to produce higher animal weight gains over a longer period than any other tropical legume. The leaf can be dried and fed as a protein supplement. Leucaena does not cause bloat (unlike alfalfa or medic). Once leucaena is established, it can last for more than 40 years. Well established plants recover readily from cutting or grazing. Vigorous leucaena plants can fix large amounts of nitrogen, improving soil fertility and the growth and feeding value of companion grass. The combination of leucaena and vigorous grass planted across the slope encourages water infiltration, reduces run-off and minimises erosion. Things to consider v Agronomic For best results, leucaena should be planted on deep fertile soils. Seedlings from direct sowing are slow to establish and do not compete well against sown grasses. Tiny psyllid insects can severely damage new leaf, especially under humid conditions. Management Leucaena is so palatable that it needs careful management to prevent overgrazing or wasteful utilisation. Leucaena foliage contains mimosine that can be toxic if leucaena comprises more than 30% of the diet. It can be fed to chickens, but only in relatively small amounts. Environmental If not cut or grazed regularly, leucaena can produce large amounts of seed, which leads to thicket development particularly along protected roadsides.
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Introduction What is leucaena? Leucaena (Leucaena leucocephala) is a deep-rooted, perennial legume shrub or tree, which rarely grows to more than 8 m tall in Eritrea (Figure 1). It has a ferny leaf like many of the Eritrean acacias, but unlike the acacias, it has no thorns. Its blue-green foliage is highly nutritious and is readily eaten by livestock. The white pompom flower-heads are 2 3 cm across and produce bunches of papery brown pods, each bearing numerous shiny brown seeds (Figure 2). The long-lived, droughttolerant plants grow best on deep, fertile soils. Being deep-rooted, leucaena can access soil moisture beyond the reach of grasses and so remains productive well into the dry season. Where does leucaena come from? Leucaena originates from Mexico and Central America, but over the last 400 years or so, and because of its many valuable properties, it has been spread around the tropics and subtropics of the world, and is now naturalised in over 100 countries. It is widely adapted in Eritrea, and is growing successfully in the Central Highlands and Western Lowlands. It is also found around Massawa, growing as an ornamental. Why plant leucaena? Leucaena has many useful characteristics, making it what is often called a multipurpose tree or MPT, and in some countries is referred to as The Magic Tree. It is a nitrogen-fixing legume and therefore improves soil fertility; it has pods and leaves of high nutritional value; it produces dense wood that can be used for fuel as well as for building and furniture; and in some countries, it is used to provide protection for shade-loving crops such as Figure 1 Leucaena tree that has not been shaped for use as livestock feed. 1 2 3 Figure 2 Leucaena: Photo 1: flower head Photo 2: pods; Photo 3: seeds. Introduction cocoa, coffee, vanilla and pepper. While leucaena has been used as human food for several thousand years, its value for feeding livestock has only relatively recently been discovered. Also in more recent times it has been quite extensively used in alley cropping systems. In northern Australia, leucaena is planted in hedgerows with grass sown in the inter-row to form a highly productive and sustainable grass/legume pasture system for cattle grazing. Once established, leucaena-grass pastures can remain productive for over 40 years. Establishing leucaena Where does leucaena grow best? Climate Leucaena is a tropical species. Although it does best under hot conditions, it can still be productive under quite mild conditions. It can currently be found growing from sea level at Massawa to over 2,000 m above sea level in Asmara. Foliage is killed by frost, but plants regrow quickly once the cold conditions are finished. Ideally the average annual rainfall should be greater than about 600 mm, although in areas of lower rainfall and deep soils where the root system can exploit moisture
Establishing leucaena at depth, it can survive and remain productive. The Central Highlands, the Western Escarpment and the South Western Lowlands mostly receive sufficient rainfall for leucaena growth. Leucaena responds to irrigation in lower rainfall areas. Soils Leucaena grows best in deep, near neutral to alkaline (ph 6 8.5), fertile, well-drained soils i.e. good cropping soils. It has the potential to produce a deep taproot, which helps plants to access moisture and nutrients well below the level of many herbaceous plants. The taproot improves its drought tolerance and increases length of growing season. If grown on shallow soils, the roots can only penetrate to the impermeable layer and are less effective. As with many forage legumes, it requires at least moderate levels of soil phosphorus and sulphur to grow well. Sulphur deficient plants are yellow and unproductive. Leucaena cannot tolerate prolonged waterlogging, especially as a seedling. However, once established it can survive short periods of excess moisture. Unlike most forage plants, it is tolerant of at least moderate levels of salt in the soil. It is best to use seed from the proven varieties... there is no guarantee that seedlings from naturalised stock will develop into good forage types. Cultivar selection There are four main forage cultivars of leucaena: Peru, the original variety used for forage, is shrubbier than the other cultivars, branching densely from near the base of the trunk. Cunningham is taller and produces more forage than Peru, but is still multi-branched and bushy if managed appropriately (Figure 3). It is a prolific seed producer. Tarramba is more tree-like than Peru or Cunningham (Figure 3), and needs more frequent height management. However, it is more vigorous, has better tolerance of cool conditions, and keeps growing under psyllid attack. It is also a less prolific seed producer. Tarramba seedlings develop faster than those of the other two cultivars, giving more rapid establishment and reducing risk of failure due to weed competition or insect attack. KX2 an interspecific hybrid developed in Hawaii, has been introduced into Eritrea by NARI. The parent species are L. leucocephala and L. pallida, the former a psyllid-susceptible, good forage type, the latter a psyllid-resistant type with low palatability to livestock. While KX2 Figure 3 Much branched Cunningham (left of white line) and less branched Tarramba (right) at NARI Research Station, Halhale. Cunningham < Tarramba >
Establishing leucaena is a good psyllid-resistant forage, it must be propagated from cuttings if it is to remain true-to-type. Seed collected from this cultivar produces plants that resemble the parent species, some palatable and some less palatable. KX2 should therefore ONLY be planted as cutting-struck stock. All cultivars have similar susceptibility to frost. It is best to use seed from the proven varieties. While leucaena is already well distributed throughout Eritrea, the source of seed used to grow these plants is largely uncertain, and there is no guarantee that seedlings from naturalised stock will develop into good forage types. Seed treatment Hard seed A proportion of the seed of many legumes is slow to germinate due to the presence of an impermeable seedcoat. This is known as hard seed, and is a mechanism in nature to ensure a spread of germination and hence improve the chances of survival of some seedlings. If all seeds germinated at once, followed by a catastrophic event such as drought or insect plague, the whole seedling population may be lost. More than 90% of freshly harvested leucaena seed may be hard, and can survive for more than five years in the soil. However, when we sow seed, we mostly want uniform germination. To do this with leucaena, we need to break the seedcoat sufficiently to let water in to the seed, without damaging the embryo inside the seed. This is done with a process called scarification. Methods of scarifying seed Several methods can be used to scarify leucaena seed.. The most reliable method is mechanical scarification, where the seed coat A proportion of the seed of many legumes is slow to germinate due to the presence of an impermeable seedcoat. This is known as hard seed Figure 4 Mechanical scarification. is physically broken by one of two methods:. Seed is placed on a hard surface and rubbed with sandpaper, being careful to only scratch the seedcoat, and not abrade it down to the creamy coloured material inside the seed.. For small amounts of seed, a tiny chip can be removed from the round end of the seed with a sharp blade (Figure 4). The round end is specified, because the embryo that gives rise to the seedling is at the sharper end of the seed. If the sharp end is damaged, the embryo will not develop.. Hot water treatment is the easiest method for larger amounts of seed, but extreme care must be taken with temperatures and times. Hot water treatment is suitable for Peru and Cunningham but not for Tarramba. Seed is placed in a gauze strainer and immersed in hot water, once again using one of two methods:. Water at 80 C for 3 to 4 minutes. Boiling water (100 C) for 4 seconds, drain for 4 seconds. In each case, use a ratio of one part seed to 8 parts hot water (e.g. 1 kg seed in 8 L water). Treated seed is spread thinly to cool and dry, or alternatively dunked into cool water briefly before spreading thinly. Either hot water treatment can result in seed death if not carried out precisely. Note: With proper calibration, mechanical scarification gives a more uniform strike, faster germination and emergence, and greater seedling vigour. Handling scarified seed Seed of any species with moisture content above about 10% does not retain its viability (stay alive), particularly at higher levels of temperature and humidity. Hence,
Establishing leucaena once seed is scarified, moisture from the atmosphere can enter, reducing the keeping quality of the seed. Scarified seed should not be kept longer than four months when stored under humid conditions. It will last longer if kept at mild temperature (below 20 C) and low humidity (less than 30% relative humidity), and so would keep fairly well in the Eritrean highlands. However, as a general rule, seed should be scarified immediately before planting. Some farmers have soaked scarified seed in water for a few hours just before planting to further speed up germination and emergence. This is not recommended as waterlogging will rot seed and the soft seed can easily be damaged (killed) during planting with mechanical seeders. Seed inoculation Leucaena is a legume, a group of plants that differs from most other plants in that many of them have the ability to fix atmospheric nitrogen. This is achieved due to the presence of rhizobium bacteria in root appendages called nodules (Figure 5). Nitrogen is important since it constitutes about 16% of all protein, which is the building block of life, and hence is important in production of meat, milk, fibre (wool) and seed (grains, pulses). The productivity of any agricultural system is strongly related to the amount of available nitrogen in that system. Unfortunately, although nitrogen comprises about 80% of the air we breathe, none of this gaseous nitrogen can be used directly by flowering Figure 6 Leucaena plants left and right are effectively nodulated; plants in the middle are not. Figure 5 N-fixing nodules on leucaena roots. University of Hawaii at Manoa. plants. It can, however, be used by certain microorganisms, including rhizobia. The rhizobia form a mutually beneficial (symbiotic) relationship with the legume. The bacteria obtain nutrient from the plant and the plant obtains fixed nitrogen in the form of ammonia (NH 3 ) from an effective strain of the bacteria. Effective nodules, that are fixing nitrogen, are pink in the middle. The productivity of leucaena stands therefore depends on the efficiency of nitrogen fixation, and this in turn depends on two factors:. The presence of an effective strain of rhizobium (Figure 6). A suitable strain of rhizobium can be mixed with the seed at the time of sowing in a process known as inoculation, either using a commercial culture of the bacteria, or by mixing some soil from around a vigorous leucaena plant with the new soil or growing medium. Soil around vigorous plants contains many effective rhizobia, so commercial rhizobium cultures have not been necessary in Eritrea.. The vigour of the plant. Weak plants do not fix much nitrogen. Lack of vigour can be due to excessive harvesting or inadequate soil fertility. As the bacteria use molybdenum (Mo) in the fixation process, and the plant uses phosphorus (P) to grow and sulphur (S) to make protein, leucaena needs these elements in adequate concentrations to ensure high levels of N fixation. Healthy leucaena pastures can fix over 100 kg N per ha each year, equivalent to over 200 kg urea fertiliser per ha. Sowing and planting Leucaena is usually established from seed which can be sown either directly into the field or into beds or containers in a nursery. It can also be struck from cuttings, but this
Establishing leucaena requires special humidified conditions, and is only necessary if propagating hybrid varieties such as KX2. Land preparation For direct sowing into larger areas, it is important to have a clean seedbed (i.e. no weeds), and to ensure there is sufficient moisture for germination and establishment. The area should be fallowed (left unplanted a period of time), using repeated cultivation to kill weeds and store soil moisture, at the same time, taking steps to control soil erosion. Establishment is most reliable with a full profile of soil moisture, as seedlings can access this moisture as their root systems develop. Direct sowing The top growth of leucaena seedlings is slow to develop because the young plants initially put most energy into development of a strong taproot. During this early phase, they are particularly susceptible to competition for water and nutrients from other plants and to damage from insects and wildlife. Make broad furrows 20 30 cm wide and about 10 cm deep in the moist, weedfree seedbed. Sow the seeds 5 10 cm apart in the bottom of the furrow and cover with 2 3 cm of soil, pressing the soil firmly around the seed. In general, seed is sown at 1 2 kg per ha, depending on row spacing. To help calculate the quantity of seed required, there are about 20,000 seeds per kilogram. Aim for a final spacing of about 30 50 cm between plants within a row. In hotter, drier areas where establishment is less reliable, sow at a higher rate using seed that is 70% scarified, leaving 30% unscarified to help overcome a false start to the season. Direct sowing Advantage: Allows plants to develop naturally where they are to be grown, with no setback to the all-important tap root development i.e. no transplant shock. Disadvantage: It is more difficult to protect young seedlings from insect attack, weed pressure and grazing by domestic livestock and wild animals. It is also often more difficult to maintain soil moisture levels during establishment. It is best to sow when the soil profile is wet to about 50 cm deep. Nursery propagation. Container plants Use plastic tubes or planter bags filled with free-draining soil, sand and composted manure in the ratio of 3:2:1 (Figure 7). Sow two seeds per tube in February/ March so seedlings are ready to be planted out at the beginning of the wet season. It is critical that seedlings are planted at the beginning of the wet season to give them the best chance of establishment. Figure 7 Leucaena plants are propagated in planter bags in a nursery. Forestry Nursery, Barentu. Water regularly as required and control weeds by hand pulling. One week after the seedlings emerge, thin to one seedling per tube. Seedlings are best grown in full sunlight if possible to ensure development of shorter, more robust plants that survive transplanting well.
Establishing leucaena Sometimes a low level of shade may be necessary to reduce evaporation and drying of the potting medium for the first few weeks of seedling growth until the root system develops. A temporary or removable shading structure is convenient for the first few weeks of growth, and should be removed as soon as seedlings are well established. Transplant seedlings when they are 2 to 3 months old. Seedlings grown under dense shade become elongated and spindly, and less hardy, and have a lower survival rate when planted out. If this does Container plants Advantage: It allows the grower to protect and nurture the plants during the early development phase. Disadvantage: Presents problems at transplanting, with transport of large numbers of bulky plants. 1 2 occur, follow the steps shown in Figure 8. It is beneficial to cut about 50% of the seedling shoot prior to planting out, especially if plants have become tall and spindly. This will help reduce transplant shock. Remove plastic tubes and place the seedling in the holes, making sure the plant is no deeper than it was in the tube. Gently pack moist soil around the root ball, and water immediately.. Bare-rooted planting Seedlings can also be raised in beds and removed for planting as bare-rooted seedlings. A nursery can be developed in a small area close to the dwelling, using waste water. It must be well protected from stock and from scavenging poultry. Household nurseries are preferable to communal nurseries, because seedlings 3 Figure 8 Transplanting leucaena seedlings from a plastic tube. If plants have become tall and spindly, cut about 50% of the seedling shooting prior to planting out (1). Remove seedling from the bag, being careful to keep soil around roots intact (2). Place the seedling upright in the hole so the root collar is level with the soil surface (3).