PROSEA, Introduction to Forages

Plant Resources of South-East Asia Introduction

List of species

Introduction

Forages and livestock

Grassland and fodder plants serve as feed for domestic and wild herbivores. They mostly belong to the families Gramineae and Leguminosae, although other herbaceous and woody plants are also eaten by animals. Grassland and fodder plants are collectively named forages. Forage can be defined as feed for herbivores, usually with low nutrient concentration and low digestibility, thus contrasting with concentrates such as grain. Forage plants can occur in the wild, but are more commonly found in grasslands, in tree crop plantations or in open spaces in and near forests and along roads, bunds between rice paddies and canals. In South East Asia such areas are sometimes termed "waste" areas - this does not mean they do not provide useful forage, but that they are not used for food or forage crops. However, forages can be cultivated and sown for the specific purpose of producing feed for livestock. Residues or by products from food crops, and weeds in cropping lands, are also very important sources of forage in South East Asia. Forage is either grazed in situ by tethered or free ranging animals or is cut and carried to penned or tethered animals. Even within one region the proportion of forage obtained from grazing as compared with hand feeding can change appreciably between different sites and seasons, as is the case for West Java (Thahar & Petheram, 1983). Although South East Asian agriculture is mostly geared to the production of rice and plantation crops, livestock play an important role in providing draft power and for the production of meat, milk and dung. The estimated livestock numbers in South East Asia comprise about 33 million cattle, 19 million buffaloes, 6 million sheep and 15 million goats (Table 1). Most animals are kept in the densely populated areas and about 90% of ruminants occur on mixed farms run by smallholders. Such farms are typically of 1-2 ha with 1-4 large ruminants and a few sheep and goats (Ranjhan, 1986). Between 1969-1971 and 1988 the estimated number of cattle, sheep and goats increased, but the number of buffaloes did not change. Yet there are differences in the trends of large and small ruminants within and between countries. For example, in Indonesia and the Philippines the number of goats increased substantially, whereas there was no such increase in Malaysia. The estimated 20% increase in the numbers of large ruminants and 68% increase in the numbers of small ruminants between 1970 and 1988 clearly point to an increased demand for fodder. Moreover, many of these animals suffer malnutrition and also the demand for meat and milk is rising as a result of increased buying power of the population, so that the increase in animal numbers may underestimate the need for increased quantity and quality of forages. It has been estimated that the demand for forage would double by the year 2000 (Remenyi & McWilliam, 1986). Although there have been considerable forage research programmes in the region (Blair et al., 1986; Halim, 1989), comparatively little use is made of improved forage plants. However, the use of these species is increasing and there is a large potential for increased forage production in the region.

1.2 Sources of forage

1.2.1 Grasslands

In tropical areas with high rainfall, grasslands are usually sub climax vegetation, because the natural climax is almost always closed forest. These sub climax grasslands have been formed by man clearing forest for shifting cultivation and are then maintained as a sub climax by grazing and burning of abandoned cropland. These grasslands are almost always found on areas that are not suited to food crops by virtue of factors such as slope and soil type. Natural climax grasslands in South East Asia are rare and usually restricted to frequently flooded lands, as has been reported for parts of Vietnam (Whyte, 1974). Grasslands are sometimes referred to as "savanna", a term that denotes a continuous graminoid stratum, more or less interrupted by trees or shrubs (Johnson & Tothill, 1985). One of the characteristics of savanna is that the climate is seasonal with wet, warm to hot periods alternating with more or less dry, warm to cool ones (Johnson & Tothill, 1985). But the term savanna is still subject to confusion and here the term "grassland" is used, defined as vegetation types in which the tree cover is less than 40% (UNESCO, 1979). Grasslands can be divided into pure (i.e. treeless) and wooded grasslands. It has been estimated by FAO (1989) that there are about 14 million ha of permanent grassland in South East Asia and the western Pacific Islands, whereas Soerjani (1970) estimated that there were 16 million ha in Indonesia alone. The dominant species in these grasslands is usually Imperata cylindrica (L.) Raeuschel. Major areas of grassland include:

• the large central plains of Thailand and the Korat plateau, which extend into Laos and the northern parts of Cambodia;
• parts of north and northwestern Thailand, extending into Burma and northern Laos;
• moderately high areas which are almost totally converted to wooded grasslands by livestock husbandry, especially on the plateaux of northern Laos and Vietnam.

The grazing lands of Indonesia are wooded grasslands resulting from degradation of climax forest. These may be the result of drier conditions combined with annual fires, as on the eastern islands (Nusa Tenggara), or they may be abandoned crop lands used for grazing. Very often these lands are impoverished as a result of frequent exploitative cropping. On Java and Madura grazing lands occupy less than 5% of the land. Nevertheless these two islands support 65% of the livestock of Indonesia, but their feed comes from roadsides, banks of canals, bunds between rice fields, open areas within and alongside forests and from crop residues. In the Nusa Tenggara region of Indonesia pure or wooded grasslands cover large areas, e.g. 35% on Lombok and 65% on Sumba and Timor. About 12% of the Philippines is grazing lands which are maintained by frequent fires. There are approximately 15 million ha of plantation crops in South East Asia (FAO, 1989). The area under many of these plantation crops is used for food crops, but often it has a herbaceous understorey of native species, or sown cover crops which can be grazed. There is a great opportunity for forage production from pastures consisting of improved forages under coconuts, and to a lesser extent under young stands of rubber and oil palm. Grazing can enhance nutrient cycling, control waste herbage and reduce use of weedicides, enable easier management of the plantation crop and may improve crop yields and income (Reynolds, 1988). The species occurring in these unimproved grasslands are native or naturalized and, except for fire, no cultural or management practices are imposed. Dry matter yields and the nutritive quality of the species are frequently low. The grass genera most commonly encountered are: Andropogon L., Arundinella Raddi, Arundo L., Axonopus Beauv., Capillipedium Stapf, Chloris Swartz, Chrysopogon Trin., Coix L., Cyrtococcum Stapf, Cymbopogon Sprengel, Dactyloctenium Willd., Digitaria Haller, Echinochloa Beauv., Eleusine Gaertner, Eragrostis v. Wolf., Heteropogon Pers., Hyparrhenia Andersson, Imperata Cyr., Ottochloa Dandy, Paspalidium Stapf, Paspalum L., Pennisetum Rich., Phragmites Adanson, Saccharum L. and Themeda Forssk. None of the species concerned, except Pennisetum purpureum Schum., is purposely established as grassland or forage crop. There are few legumes in these grasslands, some of the more common species being Desmodium heterophyllum (Willd.) DC., Desmodium triflorum (L.) DC., Mimosa pudica L., Mimosa invisa Martius ex Colla and Indigofera spp. The species composition of grazing lands changes with the climatic regime and management imposed (Manidool & Chantkan, 1986). Grass species of temperate origin (C3 species) occur at high altitudes in the region, such as on Mt Kinabalu in Sabah and on mountains in Indonesia and in the highlands in Malaysia and New Guinea (Whyte, 1974).

1.2.2 Annual and perennial fodder crops

Fodder crops in present use fall into three categories, viz. herbaceous crops, root crops, and trees and shrubs. The herbaceous crops are mostly grasses and legumes. The main grass crops are: Pennisetum purpureum Schum., P. americanum (L.) K. Schum. ex Leeke, P. purpureum × P. americanum, Panicum maximum Jacq., Tripsacum andersonii J.R. Gray, Saccharum officinarum L. and Zea mays L. The second and the last two species listed are primarily used as food crops. The main herbaceous legume fodder crops are Cajanus cajan (L.) Millsp., Lablab purpureus (L.) Sweet and Vigna unguiculata (L.) Walp. and these are used primarily as food crops, and Stylosanthes guianensis (Aublet) Swartz. The root crops used for human and animal nutrition are Manihot esculenta Crantz and Ipomoea batatas (L.) Lamk. For further information from the viewpoint of forage, see Section 1.7. Of the trees and shrubs Leucaena leucocephala (Lamk) de Wit is the most extensively used, but other species such as Calliandra calothyrsus Meissn., Flemingia macrophylla (Willd.) Merrill, Gliricidia sepium (Jacq.) Kunth ex Walp., Sesbania grandiflora (L.) Poiret and S. sesban (L.) Merrill are also important (Topark Ngarm, 1990). Trees and shrubs can be used in many ways, as living fences, vegetation in uncropped areas, hedgerows in alley cropping and as component species in intercropping (Topark Ngarm, 1990). There is great interest in fodder trees and shrubs in South East Asia (Devendra, 1990). Fodder crops are used by smallholder farmers as well as by large scale animal production units, mostly dairy farms near the larger cities. However, in most cases the cultivation of forage crops is subservient to that of food crops. Nevertheless, there is scope for forage crops in combination with food crops, either as alley cropping or undersown to provide better quantity and quality of forage after the food crop is harvested.

1.2.3 Crop residues and agricultural by products

Nearly all food crops leave residues that can be used as forage. They are a very important forage resource in South East Asia. Major sources include: rice hulls and straw, banana pseudostems, maize stover, sorghum stover, cassava leaves, sugar cane bagasse and tops, and pulse straws (Ranjhan, 1986). Residues from cereal crops are of poorer quality than residues from pulse crops and considerable research has been carried out on ways of improving their digestibility and intake (Wanapat & Devendra, 1985). The importance of different crop residues in animal feeding systems varies very widely between sites and between seasons at one site (Moog, 1986; Soedomo et al., 1986). In addition, by products from crop processing, such as rubber seed meal and oil palm meal (Tinnimit, 1985), are used as concentrate feedstuffs.

1.3 Forage and livestock production systems

1.3.1 Current inputs to forage systems

Permanent native grasslands in this region can be classed as extensive forage production systems, as there are no managerial inputs such as irrigation, fertilizer or controlled grazing. Even though the pastures may be over utilized to the point of overgrazing, the only inputs of fire and grazing are often uncontrolled. Semi intensive forage production systems have inputs such as fertilizer, weeding and irrigation primarily applied to the main cash crop, which also benefit associated forage. Intensive forage production systems have inputs applied for the sole purpose of forage production. An example of this would be large scale dairy farms near urban centres, where fertilizers could be used on planted forage crops. Based on the classification of Perkins et al. (1986), five forage production systems, each with its typical level of input, can be distinguished in South East Asia:

• extensive permanent grassland: (a) privately owned land, (b) communally grazed hill land and (c) communally grazed and cut roadsides;
• semi intensive permanent forages: (a) understorey of tree crop plantations, (b) forage from shade trees in plantations, (c) paddy field

bunds and edges of crop fields, and (d) perennial forage in alley cropping;

• semi intensive annual forages: (a) forage crops sown after harvest of food crops and (b) crop residues;
• intensive permanent forages: (a) improved grasslands, and (b) protein banks;
• intensive short term forages: (a) fodder crops, replacing food crops and (b) fodder crops on special areas.

Hay or silage is not widely used in South East Asia and is not likely to be so in the future (Ranjhan, 1986). However, conservation is successfully used in some situations. For example, in Indonesia some commercial dairy farmers are using silage of elephant grass (Pennisetum purpureum) and some smallholders are using dried grass for feed in the dry season.

1.3.2 Input of forage into different livestock production systems

All livestock production systems can conveniently be grouped into three categories: pastoralism, livestock-crop, and crop-livestock. In pastoral systems people are dependent for livestock on all their needs and there is no interaction with crops for human food. There are three main subgroups: nomadism, ranching and intensive dairying. Nomadism is widely practised in semi arid and arid areas of Africa and is not applicable to South East Asia. Ranching takes place in northern Australia and parts of South America, but is of very little importance in South East Asia. Commercial dairying in South East Asia is still restricted to areas with good access to large urban centres, but is likely to become more widespread in the future. The second or "livestock-crop" production system, where there is some dependence on crop residues for feed, but livestock are more important in the farm system than cropping, is typified by many areas in Africa, but to a lesser extent in South East Asia. The third or "crop-livestock" system is typical of South East Asia, where the crop can be an annual such as rice or a long lived tree such as coconut. The food crops are the major and essential part of the farm system. The conceptual potential for incorporating the different forage sources previously mentioned in Section 1.2 into these different systems of livestock production is summarized in Table 2. This table illustrates that there are potentially more ways of incorporating forages into crop-livestock systems than into systems such as nomadism or ranching. But this potential is restricted by several important limitations to forage production.

1.4 Main limitations to forage production

Forage production constraints in South East Asia can be attributed to climate, soil conditions, species, management and socio economic conditions.

1.4.1 Climate

In humid regions without a dry season of any significance, climatic conditions are generally conducive to good forage growth. However, even in such areas cloud cover will frequently reduce incoming radiation, resulting in lower photosynthesis. Daylength in equatorial regions can also limit growth in comparison to higher latitudes. The combination of longer days and less cloud cover in northern Australia, for example, results in more total incoming radiation than at the equator (Cooper, 1970). Forage growth under trees is also restricted through the interception of light by the tree canopy, as well as by competition for nutrients and moisture. Temperature is not a limiting factor in equatorial regions except at higher altitudes. However, as one moves away from the equator, temperature will be limiting during the time of year with the shortest daylengths. Both at high altitudes and latitudes, frosts can destroy leaves and stems or even kill the plants of tropical species, such as legumes and C4 grasses. At high altitudes, where growing conditions are temperate, the adaptation of the vegetation is reflected in the increased presence of C3 species. But at higher latitudes within and immediately north and south of the tropics of Cancer and Capricorn, the growing conditions are primarily tropical. This is because the period of adequate moisture coincides with that of high temperatures and longest daylength. The grasses occurring in these regions are mainly of the C4 type, which cannot grow at temperatures below about 15 °C (McWilliam, 1978). Rainfall is not often limiting in equatorial regions, although periods without rain of up to six weeks have been encountered (Niewolt, 1982). However, total rainfall and the period of the year in which it is received generally decrease with increasing distance from the equator. Using the classification of Troll (1966), the following tropical climatic zones can be distinguished in South East Asia (Table 3): tropical rainy climates (V1), tropical humid summer climates (V2), and wet and dry tropical climates (V3). To adequately describe South East Asia, when the region is defined in broader terms, the following subtropical climatic zones should be included: dry winter climates with long summer humidity and cool dry winter (IV4), and permanently humid climates with hot summer and maximum rainfall in the summer (IV6+7). Mountainous areas in equatorial regions pose a problem in climatic classification. From the point of view of forage plant adaptation, such areas can be regarded as equivalent to the subtropical climatic zones IV6+7 and IV4, depending on rainfall distribution. Soil moisture will be limiting in the climatic zones V2, V3 and IV4 during the period of shortest daylength, and in the latter zone this will coincide with temperature constraints. In climatic zones V3 and IV4 the unreliability of rainfall during the rainy period also imposes strong limitations on forage production.

1.4.2 Soil conditions

Soil fertility varies widely over the region. The more fertile soils are derived from basic volcanic rocks, coralline material, or alluvium. These soils are intensively cropped. Some 60% of the soils in South East Asia have severe nutrient deficiencies or toxicities (Kerridge et al., 1986), even though they have medium to excellent soil physical conditions. These soils are leached and have low organic matter levels and low cation exchange capacities. They are acid, with consequently high availability of soluble Al and Mn and low availability of P, Ca and some trace elements. Many tropical forage species, including legumes, are adapted to acid conditions and can tolerate high levels of available Al. Soils in Troll's V3 and IV4 climatic zones tend to be less acid than those in V1, V2 and IV6+7. Regional studies of soil fertility, such as described by Kerati Kasikorn (1984), can help document the severity of nutrient deficiencies on different soil types.

1.4.3 Species

The native and naturalized forage species are adapted to the prevailing climatic and soil conditions. Rainfall in climatic zones V1, V2 and IV6+7 is sufficiently regular that drought tolerance is not a requirement for the plants. Adaptation to dry conditions as a result of irregular and/or seasonally low rainfall is, however, required for plants in zones V3 and IV4. In all climatic zones soil fertility is a major constraint to growth although species differ in their adaptation to low fertility (Kerridge et al., 1986). Plant species that are adapted to the unfavourable rainfall and soil fertility have developed strong survival mechanisms. These are based on vegetative propagation and competitive ability to exclude other species (e.g. Axonopus compressus (Schwartz) P. Beauv. and Imperata cylindrica) or on the ability to produce copious seed (e.g. Mimosa pudica). High dry matter production and nutritive value are not necessary attributes for species to survive, and so some native species have low productivity and poor nutritive value. Some introduced species would not persist unless soil fertility is amended, or if they do, they are often no more productive than native or naturalized species. Conversely, some native and naturalized species may yield as much as introduced species under improved conditions of soil fertility. Introduced legumes should be checked to ensure that they are nodulated. Preferably, introduced legumes should be able to nodulate with indigenous strains of rhizobia. Species differ in their adaptation to defoliation. Some species, such as Themeda triandra Forssk., are unable to persist even under moderate grazing pressure. Other species, such as Imperata cylindrica and Mimosa pudica, avoid high grazing pressures because of low palatability while others, such as Axonopus compressus, are resistant to grazing through their prostrate growth habit. Recent research has also shown that there is considerable variation between species in their ability to grow under the reduced light conditions in plantation crops (Wong et al., 1985a, 1985b; Ahmed Tajuddin, 1991; Shelton & Stür, 1991).

1.4.4 Management

The production of forage from a given area of land depends not only on climatic and edaphic conditions. Within these given limitations the farmer has a large influence on both quantity and quality of forage harvested. The options are:

• to return removed nutrients or not;
• to fertilize or not;
• to alter frequency and height of cutting;
• to alter numbers and movement of animals which are freely grazing or are tethered on grazing land;
• to alter the integration of fodder and food crops.

The first two options are seldom applied to native forage species. In fact the usual system is to remove forage, feed it to stalled or tethered animals and to use the excrement as manure on food crops. This amounts to mining of nutrients, leading to impoverishment of the soil under forages and consequently lower forage yields. In the case of grazing most of the nutrients are returned to the field, but the distribution is very uneven and losses of inorganic nitrogen will occur through volatilization of ammonia and leaching of nitrate. A high frequency of harvesting can accelerate exploitation of nutrients and disappearance of species not morphologically adapted to frequent defoliation. On the other hand, forage harvested in a young stage of growth is of higher protein and mineral concentration and of higher digestibility than material harvested at an older stage of growth. A stocking rate exceeding the carrying capacity of a grazed area will lead to overgrazing, often resulting in the disappearance of palatable species and the dominance of species that are not readily eaten, such as Imperata cylindrica and Mimosa pudica. Even Imperata cylindrica can be eliminated by very heavy grazing and be replaced by unpalatable weeds (Falvey & Hengmichai, 1979). Overgrazing thus leads to reduced productivity of the land. The unpalatable species at least protect the land against severe soil erosion which would otherwise occur. A detailed discussion of how grazing pressure effects pasture productivity, botanical composition of pastures and animal production is given by Humphreys (1991). Food crops are the key to agriculture in South East Asia and any attempt to improve fodder production must work within this limitation. However, there are possibilities for combining quality requirements for human food as well as for animal feed in one crop. For example, rice cultivars can be selected for grain as well as straw quality, and cassava for root quality as well as for low HCN content of the leaves.

Socio economic constraints

The improvement of forage resources requires investment of money and labour and therefore depends on factors such as:

• the economic value and marketability of the animal products;
• the availability of land and its lease conditions;
• accessibility to finances, knowledge and continued support;
• motivation of the farmer and his attitude to risk;
• cultural barriers;
• economic alternatives within the farm systems.

Much animal production in South East Asia has no direct market value, as in the case of draft power. Many farmers have no land available for direct forage production, and if they do, they may not have access to finance or may not know how to improve their production of forage. In particular, there are major problems in improving communally grazed lands where any improvements are not for individual, but common use (Raghavan, 1990). Socio economic barriers are, in general, the main limitation to improving animal production in South East Asia. This is further illustrated by Ghani & Wong (1990), who list factors that constrain the adoption of improved agroforestry systems. These are factors of socio economic, socio cultural and institutional nature which are prevalent in South East Asia, as in most developing countries. The most important of these are lack of motivation, lack of finance, lack of knowledge, lack of entrepreneurship, lack of community leadership, limitations caused by customs and tradition, lack of research and extension facilities and personnel, and problems of property rights.

Overcoming limitations to improving forage resources

1.5.1 Climate

Nothing can be done to alter the macro climate for forage production, although it is possible to make the most of the potential for forage production in areas with a changed micro climate as, for example, under coconut plantations. Where irrigation is available, it is usually used to grow food crops in preference to forage.

1.5.2 Soil fertility

It is highly unlikely that inorganic or organic fertilizers will be used on a widespread basis on extensive grasslands in South East Asia in the near future. There are more prospects of fertilizers being applied to vegetables, grain or tree crops, thus having an indirect impact on forages in semi intensive systems and to intensive forage production areas. Phosphorus will be the main element required for legumes though S, K, Cu, Mo, B and Ca may also be needed. Nitrogen is the primary limitation for grasses. In grass/legume systems the legume supplies some nitrogen to the grass, but rarely enough for the grass to reach maximum yield. In some localities there is potential for increasing animal production by supplying Co and Na directly to animals, as these elements can be deficient for animals but not for plants. Many tropical forages are low in Na (Little et al., 1989). Some forage species such as Stylosanthes spp. can grow at low levels of available soil P and so can have low P concentrations in their forage. In these cases, P can be a limiting factor for animal growth when it is not limiting for plant growth.

1.5.3 Improved species

The need for new forage species is obvious, because native and naturalized species frequently lack production capacity and/or nutritive value. Improved forage species have been selected for yield potential and nutritive value, but will frequently require amendments to soil fertility and some control of defoliation to express this potential. Since the main emphasis of this book is on species and not on management, some of the very large number of native or naturalized species and potentially useful introduced species are described in detail in Chapter 2. They are also listed in Table 4, with an indication of the climatic zones to which they are best adapted. The importance of adequate nutrition and correct management in optimizing the use of these improved species is discussed in a series of reviews edited by Blair et al. (1986). There is considerable variability within many of the promising native and introduced pasture species and this variability needs to be evaluated and any weaknesses clearly defined before commencing breeding programmes. Where species are sown by seed, improving seed production can be important in reducing seed costs (Hopkinson, 1986) and in enhancing adoption by farmers. This is well illustrated by experience in Thailand where a government backed guaranteed price for seed of forage species has enabled smallholders to treat seed production as a cash crop. In 1990, about 3000 farmers participated in this programme and produced about 500 t of seed of grass and Stylosanthes hamata (L.) Taub. (Manidool, 1990). The grasses and herbaceous legumes can be used in mixtures in grasslands and under plantation crops, or separately as forage crops. The tree and shrub legumes can be used in protein banks, in alley cropping, in hedges, or as shade trees or single trees. In selecting species for improving forage production, consideration should be given to particular management requirements. For example, in cut and carry systems, erect grasses such as Panicum maximum and Pennisetum purpureum have advantages over more prostrate grasses such as Brachiaria spp. which are better suited to grazing. Ability to tolerate shading is a very important selection criterion for species under plantation crops. Ease of establishment under realistic conditions is also important and experimental studies can help to define the most appropriate establishment techniques (Wilaipon & Pongskul, 1984). It is very advantageous if legumes can nodulate readily and consistently with native rhizobia.

1.5.4 Management and socio economic constraints

In general terms, there is enough knowledge to predict the reaction of many introduced forage species to defoliation by cutting or grazing. This is shown by the many descriptions of the reaction of species to defoliation that are in the second chapter of this book, and, in the case of shrubs and trees, as indicated by Devendra (1990). However, much less is known about the potential benefits of controlled management or the introduction of herbaceous or tree legumes into natural grassland. Although our agronomic or biological understanding is still incomplete, it should be pointed out that socio economic conditions are usually a greater constraint to introducing and managing forage species than our present understanding of their biology and agronomy.

Selection of species to be included in this volume

As indicated in the previous sections, a very wide range of plant species contributes to the forage resources of South East Asia. Some of these species are native or naturalized and others have been deliberately introduced. Species evaluation throughout the region has also shown that there is considerable potential for using cultivars or accessions of forage species that have been developed in other countries. In most instances more is known about the ecology and agronomy of these introduced species than there is of the important native or naturalized species, though useful information on the agronomy of some native grasses is given by Mehra & Fachrurozi (1985) and Skerman & Riveros (1990). Forage legumes are often also cover, green manure or pulse crops, particularly in humid climates. In many cases legumes serve more than one purpose simultaneously. The cover crops in plantation agriculture are grazed by or cut for domestic animals and the green manure crop can also be grazed or cut before being allowed to grow before being ploughed in. It would be impossible to give details about every forage species used in South East Asia in this book, so the species included in Chapter 2 were selected after consultation with specialists throughout the region. Important native and naturalized forage species were included, provided there was sufficient agronomic and ecological information. Section 1.7 gives some information about the forage properties of selected species that are primarily used for food crops, but where some parts of the crop are used for forage. (e.g., sugar cane, cassava and rice). In these cases, botanical and other relevant information will be included in the appropriate Prosea volumes. Forage species that are commercially available from Australia and South and Central America, which are as yet little used in South East Asia, have also been included. Many of these species are showing considerable promise in South East Asia and are being used or are recommended for use on farms. They are also frequently mentioned in current documents such as journals or workshop proceedings. It was therefore appropriate to include them in this book so that their evaluation and subsequent use in farms may be made faster and more efficient by making readers more aware of their strengths and weaknesses. Some temperate and subtropical legumes have been included as they show potential in highland areas (e.g. Nurjaya et al., 1983). An enumeration of species which were not included in Chapter 2, but are known to be used as forages, is presented in Chapter 3. Although it does not include every species which is eaten by animals, it includes the species noted in the historical handbooks on plants of economic value in South East Asia as being used for forage. Forages with another primary use are listed in Chapter 4. Information given under the headings such as "Properties" and "Yield" which refers to nutrient concentrations or dry matter yield is usually only in the form of broad ranges. These properties are much more variable than they are in the case of commodity groups such as pulse crops. They vary with the age of the material sampled, the grazing or cutting regime practised, soil fertility, and climatic conditions during the growth period prior to sampling. Consequently, it is usually misleading to quote specific figures or even narrow ranges of nutrient concentration and yield. Where ranges are quoted, they merely serve to give some idea of the values that are likely to be achieved under the usual conditions of field variability. Furthermore, if pastures are grazed, the quality of the material ingested by animals will depend upon the opportunities for selective grazing.

Species primarily in cultivation as a food crop

Practically all grass and legume species which are palatable to livestock and of adequate yield and quality are used as forage. The primary use of some species depends on local conditions, tradition and on the availability of certain types of food. For example, Cajanus cajan, Lablab purpureus, Macrotyloma uniflorum and Vigna unguiculata are important pulse crops in many parts of Asia, but used only as forage in Australia. Oryza sativa, Pennisetum americanum, Saccharum officinarum and Zea mays are cereal and sugar producing crops and Manihot esculenta is a starch crop in much of the tropics, but in many places they are solely or partially used as forage. In addition, when these crops are used for food, they leave residues that can be used as forage. Some information relating to the forage qualities of the species just mentioned follows below. The species are treated in detail in other Prosea volumes. Cajanus cajan (L.) Millsp. (pigeon pea). A short lived perennial shrub which can be grown as a protein bank or in alley cropping systems mixed with other food crops or grass as forage. The shrubs must be well established before they can be grazed intermittently, cut for forage, hay or silage. Defoliation should be lenient to achieve maximum persistence of up to about 5 years. It can produce DM up to 25 t/ha per year. Pigeon pea hay, made when a large percentage of pods are mature, serves as a substitute for industrial concentrate feed. The N concentration varies between 2.5% and 4.5%, and the plant is a good source of vitamin A. At the young stage, pigeon pea is not highly palatable, but it is readily eaten in the green pod stage (Skerman et al., 1988). Lablab purpureus (L.) Sweet (lablab). An annual or short lived perennial crop with potential to provide early dry season forage when sown at the end of the rainy season. It can be leniently grazed 10 weeks after sowing, 2 or 3 times in a season, but is not tolerant of heavy grazing. Livestock may require a few days before readily accepting the green material. Lablab can be cut for hay or silage. Dry matter yields of 20-30 t/ha can be expected during a 4-6 month growing period, with an N concentration of 2.5-4.2% and a DM digestibility between 50-65% (Skerman et al., 1988). Macrotyloma uniflorum (Lamk) Verdc. (horse gram). An annual herb grown in the rainy season, with reasonable drought tolerance, which can be used as a dry season feed reserve. Dry matter yield of 6.6 t/ha, consisting of over 2 t of seed, has been recorded in Queensland (Australia). N concentration ranges between 2.5-4.0% (Staples et al., 1983). Manihot esculenta Crantz (cassava). A perennial shrub with storage roots consisting mainly of starch. The roots and leaves are used as livestock feed, but both may contain high levels of cyanogenic glucosides (HCN), which can be poisonous if eaten in large quantities. Heat treatment of roots and wilting of green leaves detoxify the material sufficiently for safe use. The roots have an N concentration of about 0.5%, but leaves may contain up to 5% N. Cassava leaves are an excellent supplement to poor quality forage. Oryza sativa L. (rice). An annual grass grown in either upland (dry) or lowland (flooded) conditions. Floating rice has a long vegetative growth period, and in deepwater rice areas in Bangladesh, India, Thailand and the Philippines the green vegetative material is harvested for forage for livestock, without reduction of the grain yield. N concentration of rice herbage ranges between 1.5-4.0%. The in vitro DM digestibility 40 days after transplanting lies between 70-84%. Deepwater rice cultivars have a greater nutritive value than lowland rice cultivars. In addition, throughout South East Asia rice straw and bran are important livestock feeds. N concentration of rice straw ranges from 0.5-1.6% depending on maturity and cultivar and DM digestibility is about 50%. Straw quality can be marginally improved by treatment with urea. Rice bran is high in energy, but the N concentration varies greatly and ranges between 0.5-3.8% (Lopez & Vergara, 1988). Pennisetum americanum (L.) K. Schum. ex Leeke (pearl millet). A robust annual grass used as a cereal crop in Africa and India, but elsewhere mostly as forage. Pearl millet should be grazed frequently but leniently, or cut at about 6 week intervals. DM yield up to 20 t/ha can be obtained with N concentration of young regrowth ranging from 2.4-3.8% and DM digestibility from 60-75%. Young pearl millet is very palatable (Skerman & Riveros, 1990). Saccharum officinarum L. (sugar cane). A tall perennial grass used for the production of sugar and as a dry season forage for livestock. Sugar cane has a high sugar content, but low N concentration (1.0%). DM digestibility at stage of harvest is about 50%. The tops of sugar cane grown for sugar production or the whole crop can be cut for hand feeding or chopped for silage (Skerman & Riveros, 1990). Vigna unguiculata (L.) Walp. (cowpea). An annual pulse crop which is also grown as a forage crop for grazing or cutting for hay or silage, giving DM yields of about 5 t/ha with a N concentration ranging from 2.5-4.5%. Cowpea is quite palatable to livestock after they have become accustomed to it in a few days. It can be grown together with annual grass forage crops (Skerman et al., 1988). Zea mays L. (maize). A tall annual grass grown for grain or forage for fresh feeding or silage. Maize can yield up to 8 t/ha of DM, with a high energy content and N concentration ranging from 2.4% in young leaves to 1.4% in 10 week old material (Skerman & Riveros, 1990).

Prospects

In most parts of South East Asia animal production based on forages is one way of increasing the incomes and security of smallholder farmers. Although all the arable land in densely populated areas is usually already in use, there are still opportunities to either collect or cultivate forage to feed animals. The main restriction will often be lack of surplus labour. Despite the importance of socio economic limitations to forage production, there is ample evidence that improved practices will be adopted. This is illustrated by the use of Stylosanthes spp. in the dry tropics of Thailand, the use of Leucaena leucocephala in many countries and the promising early adoption of the "three strata farming system" in the drier areas of Indonesia (Nitis et al., 1990). The agronomic areas where there is likely to be the greatest potential for improvement, within existing socio economic conditions, are in the use of shrub or tree legumes, backyard or home garden forage production, making better use of bunds between rice paddies, forage under plantation crops - particularly coconuts, and use of annual legumes with or after food crops. Recent progress in improving animal production by shrub legumes or by forages under plantation crops has been reported by Devendra (1990) and Shelton & Stür (1991), respectively. A small but increasingly important system with the potential for improvement is that involved in the supply of milk to urban areas. If improved forage systems can be effectively incorporated into individual smallholdings, as in the case of the "three strata farming system", there is more likely to be ready acceptance of improvements than when they affect a community, as in the case of common grazing land. Forage improvement schemes will be accepted by a community much more easily, if the community "owns" the scheme rather than if the scheme is imposed on the community. Nevertheless, governments can also encourage improvements, as in the case of leucaena and other shrub/tree legumes in Indonesia (Rangkuti et al., 1990) and the Philippines (Trung, 1990) and through the development of "mini farms" in Malaysia (Chin, 1989). It is highly desirable to have an effective and sustained educational and "follow up" scheme to support farmers adopting any improved practice (Nitis et al., 1990). The key point is that although the constraints imposed by socio economic factors must be recognized, they are not insurmountable (Perkins et al., 1986). There are many forage species to choose from and proven species are available for all climates in South East Asia. This diversity should be utilized as much as possible, because it is undesirable to rely on one or a few species or cultivars. Reliance on a narrow germplasm base has the danger that a pest or disease will destroy all or a large part of the feed supply and thus endanger the income of farmers. This was well illustrated by the hardship experienced by farmers who were relying heavily on Leucaena leucocephala prior to the advent of the leucaena psyllid in South East Asia (Trung, 1990).