3. PASTURE SPECIES

3.1 Introduction: Grasses and Legumes

3.1.1 Grasses

- grasses belong to the broad family Graminae (Poaceae) with about 10,000 species and between 650 and 785 genera (Bogdan, 1977; Watson and Dallwitz, 1992), of which only 12 to 15 genera of tropical grasses are widely used in sown pastures. However, most genera do have more than one important sown species (Whiteman, 1980).

The morphology of grasses has been described in numerous books (Bogdan, 1977; Holmes, 1980; Wallis et al., 1977). The main parts of the grass plant are illustrated in Figure 47. Most grasses have similar features although growth forms can vary from tufts, tussocks or bunches to prostrate, creeping or straggling types. The nature of the growth form usually determines the response of a grass to cutting and management and may determine the type of planting material available.

Two of the most important features of tropical grasses found in countries with pasture-cattle-coconut systems are:

1. The kinds of stems associated with the various species.

2. The ability of various species to produce viable seed.

While a number of tropical grasses have erect culms, usually forming tufts, tussocks or bunches, with the growing point near the level of defoliation and are propagated from seed or splits from the existing plant, others have stems that creep along the surface of the ground (stolons) or below the ground (rhizomes) and tend to form a sward rather than tufts (Wallis et al., 1977). The characteristics of stoloniferous plants are to cover the ground surface with decumbent or prostate culms, to root at the nodes and to be vegetatively propagated by planting material taken from the existing plant. These are important characteristics where relatively inexpensive labour is available for pasture establishment, where viable seed either may not be produced or is expensive to import and where it is expensive and difficult to maintain stocks of it.

It is possible to recognize three main type of grasses, although the third group is relatively minor in terms of grazed pastures as most species are likely to be used for cut forage:

1. Bunch or tufted grasses - form clumps or tufts; if allowed to set seed, will spread when seed falls to the ground and germinates (e.g., guinea grass - Panicum maximum).

2. Stoloniferous grasses - send out stems or stolons along soil surface, rooting at the nodes and producing new shoots (e.g. para grass - Brachiaria mutica).

3. Rhizomatous grasses - send out stems or rhizomes below soil surface (e.g., Guatemala grass - Tripsacum laxum).

3.1.2 Legumes

- legumes belong to the broad leguminosae family with about 16,000– 19,000 species in about 750 genera which is divided into three distinct sub-groups: Mimosoideae, Caesalpinioideae and Papilionoideae (Allen and Allen, 1981; Bogdan, 1977). Almost all the important pasture legumes belong to the Papilionoideae, with several browse plants and woody species in the Mimosoideae. Papilionoideae includes up to 200 genera and 12,000 species, distributed throughout the world. Grasses and legumes are similar in that only a small number is used commercially in pasture production.

Figure 47. - The grass plant (Tothill and Hacker, 1973).

The morphology of legumes is described by Bogdan (1977), Wallis et al., (1977), and others. Some of their important characteristics are:

• some legumes are creeping types and root at the nodes of the stolons, can also reach sunlight by climbing on the associated grasses (see Figure 48);

• on the root systems of most legumes nodules may develop in which nitrogen-fixing bacteria of the genus Rhizobium form a symbiotic relationship with the plants (see Figure 49);

• large amounts of nitrogen may be fixed through the action of their root nodules (Walker, 1983);

• good grazing management is needed to maintain a fair proportion of them in a pasture;

• because of their high protein content they improve tropical pasture, thus having a direct bearing on the level of animal production (Jones, 1972).

Figure 48. - Siratro Climbing on Silk Sorghum.

Figure 49. - Nodules on the root system of Sesbania sesban.

3.2 Comparison of species: tufted or bunch v. stoloniferous grass species

In terms of establishment, management and ease of locating fallen coconuts, tufted or bunch grasses and stoloniferous species have advantages and disadvantages regardless of the individual species used.

3.3 Indigenous v. exotic species under coconuts

Traditionally, where cattle were used as ‘sweepers’ to keep weeds between coconut trees short enough to find the fallen coconuts, the pastures consisted of a large number of indigenous species, some quite productive, others of poor quality.

The more promising of these include: carpet or mat grass (Axonopus compressus), St. Augustine or Buffalo couch grass (Stenotaphrum secundatum), Pemba grass (Stenotaphrum dimidiatum), Cogon (Imperata cylindrica), Tee grass (Paspalum conjugatum), as well as various legumes such as alyce clover (Alysicarpus vaginalis), Desmodium ovalifolium, Desmodium triflorum, hetero (Desmodium heterophyllum) and sensitive plant (Mimosa pudica). Stur and Shelton (1991a) have listed some of the more important naturally occurring grass and legume species in coconut plantations in South East Asia and the Pacific (see Table 38). Weeds include Ageratum conyzoides, Anona muricata, Asclepias curassavica, Asystasia intrusa, Blechum pyramidatum, Borreria latifolia, Borreria laevis, Cassia tora, Castilloa elastica, Clerodendron fragans, Clidemia hista, Codiaeum variegatum, Cyperus aromaticus, (Kyllinga polyphylla), Eremochloa ciliaris, Eupatorium odoratum, Hyptis capitata/pectinata/rhomboides, Ischaemum muticum, Lantana camara, Microstegium ciliatum, Mikania cordata, Mikania micrantha, Mimosa invisa, Nephrolepis biserrata, Nephrolepis hirsutula, Ottochloa nodosa, Psidium guajava, Pseudo-elephantopus spicatus, Pteridium sp., Ruellia prostrata, Sida acuta, Sida glomerata, Sida rhombifolia, Solanum torvum, Sporobulus indica, Stachytarpheta urticifolia, Synedrella nodiflora, Themeda villosum and Zoysia matrella (Chen and Shamsudin, 1991; Cheva-Isarakul, 1991; Evans et al., 1990; Reynolds, 1981; Steel et al., 1980; Whistler, 1983; Wong et al. 1988, 1988a; Mukherjee, 1988; Trung et al., 1989).

Eng (1989) notes that some 60 native species have been recorded under the plantation canopy, of which more than half have been found to be palatable and nutritious enough for animal production, especially the commonly occurring Asystasia intrusa. Native vegetation under coconuts varies according to location and intensity of grazing. Moog and Faylon (1991) noted the effect on botanical composition of heavy grazing by buffalo for three years in Sorsogon (Philippines). Pasture composition changed from Imperata cylindrica and Pueraria phaseoloides domination to a weed dominated sward (See Table 39). Control of stocking pressure and modest fertilizer applications were recommended to obtain and maintain a desired pasture composition; otherwise undesirable weed species may gradually dominate the sward (see Figure 50).

Table 38. - Natural vegetation occurring frequently in coconut plantations in Southeast Asia and the Pacific (modified from Stur and Shelton, 1991a)

Table 39. - Botanical composition (%) of native pasture before and after three years of grazing by buffalo under coconuts in Sorsogon (after Moog and Faylon, 1991)

Figure 50. - Overgrazed weed dominant pasture.

Where the main aim is to keep weeds under control in native pastures, productivity may vary from low to moderate depending on the relative percentage of productive grass, legume species and weeds, particularly bush weeds. For example, in Western Samoa local pastures dominated by Mimosa pudica and hereto were considered to be particularly productive (Reynolds, 1981, 1982c) while in the Solomon Islands there was no significant difference in liveweight gains between improved pastures and naturalized pastures with a high legume content and consisting of Axonopus compressus, Mimosa pudica, Centrosema pubescens and Calopogonium mucunoides (Watson and Whiteman, 1981a). However selective grazing may result in the disappearance of the more palatable species while the less palatable become dominant. Using cattle as ‘sweepers’ or ‘weeders’ without additional selective weed control measures may control the weeds in the short term but allow tough unpalatable species to become dominant (Ohler, 1984).

Where the aim is to do more than merely keep weeds under control so that fallen nuts can be located, then various exotic species are available. Each has certain characteristics and may be suited to particular physical, socio-economic and management conditions. Important characteristics are:

• yield
• palatability
• nutritive value
• ease of propagation
• rapidity of establishment
• ability to compete with weeds
• pest and disease resistance
• ability to associate with other pasture species
• adaptability to local soil, climatic conditions, management levels and in terms of coconut environment, shade tolerance and degree of competitiveness with coconut trees
• ability to withstand high grazing pressure
• persistency.

Characteristics have been discussed in detail by Cameron (1980), Whiteman (1980) and Whiteman et al. (1974).

3.4 Pasture species suitable for coconut environment

A wide range of different grass and legume species has been reported in early investigations carried out in different countries:

More recent studies and reports are now available for:

Reviews and information summaries on pasture species are available in the following: Anon. (1967b); Bourgoing (1990); FAO (1983d); Guzman and Allo (1975); Humphreys (1981, 1991); Lane (1981); Mack (1991); Nair (1983); Ohler (1969, 1974); Payne (1985); Plucknett (1972, 1979); Reynolds (1978e, 1980); Rika (1986); Shelton et al. (1986, 1987a); Stur and Shelton (1991); Thomas (1978) and Whiteman (1980).

Among species referred to are:

In Sri Lanka it was noted that B. miliiformis was more shade tolerant than B. brizantha (Santhirasegaram and Ferdinandez, 1967) and that P. maximum was a very competitive grass. However, it could successfully be used in the wet zone without any reduction of coconut yields provided both crops were adequately fertilized (Santhirasegaram et al., 1969). The effect of various species on coconut yields was particularly noted (Santhirasegaram, 1966b, 1966c). Ferdinandez (1978) evaluated a number of species under coconuts (see Table 40) and surprisingly (in view of its low shade tolerance shown elsewhere) Digitaria decumbens outperformed even Brachiaria miliiformis.

Another pasture grass that has produced promising results at Coconut Research Institute (CRI) is B. dictyoneura which outyielded B. miliiformis by 40 percent (Ibrahim and Ferdinandez, 1983). Centrosema was found to combine well with B. miliiformis, D. decumbens, B. ruziziensis and P. maximum (Ferdinandez, 1978).

Table 40. - Dry matter yields of pasture grasses grown under coconuts (Rajaguru, 1991 after Ferdinandez, 1978)

All plots received 200 kg N ha^-1.

In the late 1970's the major practice under coconuts in Sri Lanka was to plant B. miliiformis with P. phaseoloides and graze with cattle tethered to trees (UNESCO, 1974). Jayawardena (1985) suggests that B. miliiformis and B. ruziziensis are the main grass species grazed under coconuts, while Fernandez (1972) selected B. brizantha and B. ruziziensis as the best species for grazing. Liyanage (1986) lists B. miliiformis, B. brizantha, B. ruziziensis, B. mutica, B. dictyoneura and Digitaria decumbens as suitable grasses for grazing, with P. maximum, Green panic, Hamil grass, Setaria sphacelata, Pusa Giant Napier and NB-21 Hybrid Napier as fodder species. Suitable legumes include Puero, Calopo, Centro, Siratro, Stylosanthes sp. and Mucuna utilis as well as the bushy legumes Leucaena and Gliricidia. Particularly impressive was (see Table 41) Brachiaria dictyoneura (Ibrahim and Fernandez, 1983).

Table 41. - Productivity of various grasses grown for three years under coconuts at two levels of nitrogen (from Ibrahim and Fernandez, 1983).

LSD (P<0.01) between species = 1045; LSD (P<0.05) between levels of N = 494.

Of the legumes, centro mixes well with Brachiaria sp. as does Siratro, but the problem with Siratro is its low productivity and susceptibility to Rhizoctonia leaf rot in the wet and intermediate zones. The suitability of stylo and Desmodium species for coconut areas is still not conclusive and wider testing is needed (Liyanage, 1991). Gliricidia sepium and Leucaena leucocephala have been evaluated under coconuts. Planted 2.0 × 0.9 m in double rows in mature coconut plantations and lopped at 3-monthly intervals they produced respectively 7–10 t ha^-1 and 12–16 t ha^-1 of green matter and 8–15 t ha^-1 and 14–20 t ha^-1 of fresh firewood during the first and second years after planting (Liyanage and Jayasundera, 1987).

Jayawardena (1988) noted that fodder grasses like Guinea and Setaria can produce dry matter yields of 15–18,00 kg ha^-1 yr^-1.

In the model integrated system for coconut small holdings Liyanage et al. (1989) used Leucaena leucocephala, Gliricidia sepium, Brachiaria miliiformis and Pueraria phaseoloides or Centrosema pubescens.

Dissanayake and Waidyanatha (1987) evaluated the performance of 10 tropical forage grasses interplanted with rubber (and their influence on the growth of the trees) over a 2.5 year period from September 1977 to March 1980. Spaces of 1.0 and 1.5 m radius were left around the rubber trees and the grass cover was grown in a 3.0 m circular area around the trees. Dry matter and crude protein yields and the effect on height and girth of 2.5 year old rubber trees were measured. Taking into consideration the effect of grasses on the height and growth of the rubber trees it was concluded that B. brizantha, B. decumbens and P. maximum (B) were most competitive, P. plicatulum, S. sphacelata and Green Panic were least competitive, while P. maximum (A), P. purpureum, B. ruziziensis and B. miliiformis were moderately competitive. A number of legumes were tried with various grasses but P. phaseoloides and C. pubescens failed to persist under repeated zero grazing (cutting). S. guianensis cv. Schofield was more resilient. Waidyanatha and Dissanayake (1985) concluded that livestock could be integrated with rubber under a zero grazing system.

In Jamaica, P. maximum was shown to be superior to Digitaria decumbens on poorer soils and in lower rainfall areas, but both grasses required appropriate fertilizers (Anon., 1971b).

In Brazil, Schreiner (1987) assessed the tolerance of four forage grasses to 0, 25, 50 and 80% shading in plot trials carried out from 1982–1985. Average yields were reduced by only 5% with 25% shading, but 50% and 80% shading reduced yields by 41% and 78%, respectively. With 50 or 80% shading yields in the first season were highest in Brachiaria decumbens, but in the second season with 50% shading yields of Digitaria decumbens and Hemarthria altissima were higher than those of B. decumbens and with 80% shading yields of B. decumbens and D. decumbens were similar and that of H. altissima was only slightly lower. Paspalum notatum generally performed less well than the other species. The concentration of N in grasses increased with increased shading.

In Bali the legumes C. pubescens, S. guianensis, L. bainesii and M. atropurpureum gave a satisfactory performance (Steel and Humphreys, 1974). Nitis and Lana (1978) noted that B. decumbens withstood heavy grazing better than Paspalum plicatulum and P. maximum var. trichoglume, Siratro increased as the stocking rate increased (although Centro and Stylo declined), while the amount of crude protein on offer ha^-1 was significantly lower at the higher stocking rates. More recently it has been reported that B. decumbens cv. Basilisk and C. pubescens were the most successful species over a six year period, while S. guianensis cv. Endeavour played a useful pioneering role in the first two years (Rika et al., 1981). Winaya et al. (1983) reported that the growth of Brachiara decumbens under shade was much thinner and weaker than in the open.

In screening trials in Indonesia to identify forage species for rubber plantations Sanchez and Ibrahim (1991) noted that Asystasia intrusa, often regarded as a noxious weed (Chee and Ahmad Faiz, 1991) showed remarkable shade tolerance, good nutritive value, high palatability and excellent seed production for establishment and self-propagation. Burns et al. (1993) in studying the quality of Asystasia intrusa as influenced by shade and nitrogen fertilization concluded that “this weed could be a useful forage for ruminants”.

In North Sulawesi, Indonesia, Kaligis (1993) noted that annual burning of Imperata cylindrica pastures under coconuts degrades soil fertility levels and damages the coconut palms. Trial plots were established with Brachiaria decumbens, Calopogonium mucunoides, Gliricidia sepium and Calliandra calothyrsus.

In the Philippines the most common legumes were C. pubescens, C. mucunoides and P. phaseoloides with centro being the most persistent (UNESCO, 1979). The main grasses used were P. maximum (in Davao), B. mutica (in Agusan) and D. aristatum in Misamis Oriental and Camiguen Island, where the soils are poorer. L. leucocephala, S. guianensis cv. Cook, M. atropurpureum and B. decumbens are also used (Faylon, 1982; Guzman, 1974; Javier 1974; McEvoy, 1974). More recently, Parawan (1991) indicated that in most parts of the Philippines the exotic grasses and legumes planted under coconuts are Brachiaria mutica, Panicum maximum, Dichanthium aristatum, Centrosema pubescens, Calopagonium mucunoides, Macroptilium atropurpureum, Pueraria phaseoloides, and Leucaena leucocephala. Improved grasses to be introduced to coastal coconut areas should be able to tolerate salinity. Included in this group are B. mutica, P. maximum, P. purpureum, D. aristatum, C. gayana, C. pubescens and L. leucocephala. In conditions where recommended exotic pasture is grown and adequate fertilizer and moisture are available, the stocking rates can be doubled or tripled with concomitant increases in copra yield of 10–20 percent (Guzman and Allo, 1975). It was noted that Setaria splendida + Centro pasture outyielded Brachiaria decumbens + Centro pastures.

However, Parawan (1991) suggests that even though the Philippines has the largest area of coconuts in the world, there are only small areas of improved pasture under tree crops. The usual ground cover consists of indigenous species. On Luzon, Trung et al. (1989) conducted a two-year study to make a realistic assessment of the stocking rate of native pastures under coconut for sheep and goats and noted that Axonopus compressus, Paspalum conjugatum, Cyathula prostrata and Zingiber zerumber flourished in the wet season, while Cyrtococcum sp., Centrosema pubescens, Desmodium triflorum, Blechum pyramidatum and Pseudoelephantopus spicatus thrived in the dry season (Palo, 1991). Mean botanical composition was 47.3% grasses, 14.3% legumes, 36.7% broadleaves and 1.7% shrubs/trees.

In another report Trung et al. (1989a) noted that the stocking rate of native pastures under coconut was approximately 10 small ruminant equivalents ha^-1 (with a range from 5–15). The predominant grasses were A. compressus, P. conjugatum and Cyrtococcum sp. with legumes M. pudica, P. phaseolides and P. lobata and the weed Ageratum conyzoides.

In Mindanao, some 20 percent of coconut livestock farms had improved pastures (Parawan, 1991a after de Guzman, 1970). Among sheep producers utilizing plantation crops, only 3.5 percent had improved pastures (Faylon, 1989). In an evaluation of 13 grasses and 12 legumes under coconuts, Subere and Gerona (1986) found that the highest producers were Setaria cv. Nandi, napier, guinea and Kennedy ruzi with average annual herbage yields (in t ha^-1) respectively of 25.45, 21.08, 18.86 and 18.26. Of the legumes Calopo was the highest yielding at 13.68 while leucaena produced 10 tons ha^-1 yr^-1. In Western Mindanao, Brachiara decumbens, Brachiaria humidicola and Setaria splendida gave good dry matter yields under coconuts (Parawan, 1991). Magat and Cadigal (1976) reported from Davao (in Mandanao) that various pasture legumes grown under coconuts yielded in the following descending order: Kudzu (Pueraria phaseoloides) > Endeavour stylo > Schofield stylo > Siratro > Centro > Townsville stylo (with Townsville stylo at 8.55 t yielding less than half as much as Kudzu at 20.53 ton ha^-1 yr^-1 of DM).

Repollo (1985) assessed the performance of various grasses and legumes under the shade of seven-year old cashew trees spaced at 9 m × 9 m. B. brizantha showed the most potential either planted alone or in combination with S. guianensis and C. pubescens.

Moog et al. (1993) reported on demonstration grazing trials with B. decumbens, B. decumbens - Centro, B. humidicola and Paspalum notatum in Bicol Region.

Moog and Faylon (1991) noted that Guinea grass and Para grass are the most commonly planted grasses under coconuts in the Philippines. Extensive areas of para grass pastures are grown in Mindanao, particularly in the Davao area. Guinea grass is more popular in Quezon province among smallholder farmers who use a cut-and-carry system. Signal grass (Brachiaria decumbens) is becoming popular under coconuts in Sorsogon where it is considered to be more productive than para or guinea grass.

Parawan and Ovalo (1987) indicated that under mature coconuts native species recorded an annual dry matter production in t ha^-1 of 4.00 when cut every 35 days and 4.36 when cut every 70 days. Setaria sphacelata var. splendida/Centrosema pubescens and Brachiara decumbens/Centrosema pubescens pastures produced 14.62 and 15.45 t ha^-1 and 10.76 and 11.41 t ha^-1 respectively under the same cutting regimes. Average carrying capacity of good native pasture is 7–15 head of sheep and goats under grazing and cut-and-carry. Average daily gains for sheep and goats range from 33–54 g. Improved pastures under coconuts (comprising mainly mixed swards of Setaria splendida - Centrosema pubescens and Brachiaria decumbens - Centrosema) yielded 7–15 tons of organic dry matter ha^-1 yr^-1. The maximum carrying capacity under such conditions ranged from 20–28 heads ha^-1 of goats and sheep (grazing). Crossbred goats showed average daily gains of 61 g while native sheep produced gains of 44–56 g. An optimum stocking rate of 20 goats ha^-1 was observed in a B. mutica-Siratro pasture under coconuts utilizing grazing and a cut-and-carry system.

In Thailand (Vijchulata, 1991) investigations to identify suitable shade tolerant forage species for the local environment were carried out and reviewed by Manidool (1984) and Cheva-lsarakul (1991). P. maximum and B. decumbens grown with C. pubescens produced higher herbage yields than B. mutica. The latter, although easily propagated, became heavily weed infested in the third year (Boonklinkajorn, 1978). Brachiaria ruziziensis and Brachiaria miliiformis have also shown promise and were regarded by Manidool (1983, 1984) as the most promising grass species in coconut plantations. B. decumbens gave a better response to fertilizer than Axonopus compressus and Paspalum conjugatum with P. conjugatum responding better than A. compressus. Desmodium ovalifolium occurs widely in the south of Thailand. In a comparative trial in Narathiwat province, Egera et al. (1989) obtained the highest dry matter yield from B. ruziziensis, followed by Panicum maximum, B. humidicola and B. miliiformis under coconut (although B. miliiformis and P. maximum gave the highest dry matter yields under rubber). Suitable shade tolerant legumes were Centrosema pubescens (Manidool, 1984) and Desmodium heterocarpon (Saphanodora, 1989a). Manidool (1984) reported that B. brizantha, P. maximum and B. mutica grown in association with coconuts cause a serious reduction in the magnesium content of the coconut fronds. He also suggested that if grasses with a high K requirement (such as P. maximum) are included in a pasture-coconut programme, that adequate amounts of K fertilizer should be applied.

Under one year old rubber B. brizantha, P. purpureum and P. maximum cv. Hamil produced the highest yields in cutting trials (Cheva-Isarakul, 1991) whereas with a cut-and-carry system under longan and lychee orchards in Chiang Mai and Lampoon provinces in N. Thailand, B. mutica is preferred for dairy cattle. Manidool investigated the production of grasses and legumes in a 11 year old sweet tamarind orchard and reported highest yields with P. maximum cv. Hamil, B. mutica and B. ruziziensis (Cheva-Isarakul, 1991).

Observation trials in Zanzibar indicated B. decumbens, B. humidicola, P. maximum, P. purpureum cv. Gold Coast, P. commersonii. S. dimidiatum, C. pubescens, L. leucocephala, Teramnus labialis and S. guianensis cv. Schofield as promising species with G. sepium/maculata replacing L. leucocephala on acid soils under coconuts (Reynolds, 1983).

Grazing cattle under coconuts has been a major agricultural activity in Papua New Guinea since the early 1930's. In the Morabe district, with a rainfall of 1400–1500 mm year^-1, the best species for use under coconut palms are B. mutica, P. purpureum, P. maximum, P. maximum var. trichoglume, B. ruziziensis, C. pubescens, L. purpureus, L. leucocephala, M. atropurpureum and M. phaseoloides (Hill, 1969; Sajise, 1973).

Detailed studies of the effect of shade on pasture species have been carried out in the Pacific region (see section 2.3). Besides the work conducted by Ranacou (1972), Eriksen and Whitney (1977, 1981, 1982) and Gregor (1972), Whiteman et al. (1974) showed that D. intortum was even more shade tolerant than C. pubescens. Steel and Whiteman (1980), reporting on a detailed evaluation of grasses under coconuts et Dala, Malaita in the Solomon Islands, indicated that although P. maximum cv. Embu, B. miliiformis, B. decumbens and B. ruziziensis were the highest yielding grasses in the first year, there was, with time, a decline in yields due to low light conditions (mean light transmission of 31 percent). In the second year, the slower to establish B. brizantha was the highest yielder while B. mutica had virtually disappeared by the end of the second year thus demonstrating its intolerance to shade. The conclusion was that none of the grasses tested were capable of producing sustained high yields presumably because of the very low light levels. However, at light transmission of 50 to 55 percent Batiki grass was both productive and persistent (Litscher and Whiteman, 1982).

I. indicum and D. caricosum are major grass species used in Fiji with some use of B. mutica, B. humidicola, P. maximum cv. Embu and M. atropurpureum (UNESCO, 1979). However, Singh and Naidu (1973) indicated that I. indicum (or aristatum) had a detrimental effect on the growth and yield of coconut palms.

In the Solomon Islands under heavy shade I. aristatum, B. decumbens, P. phaseoloides and C. pubescens were the best species, while under less shade B. dictyoneura, M. atropurpureum and V. luteola showed promise (Gutteridge and Whiteman, 1978).

In Vanuatu, various reports have noted the role of buffalo grass (Stenotaphrum secundatum) as a shade tolerant species under coconuts with the ability to tolerate heavy grazing (MacFarlane and Shelton, 1986; Weightman, 1977). Native species include Axonopus compressus and Paspalum conjugatum. MacFarlane and Shelton (1986) mention new improved species including Signal grass (Brachiaria decumbens) glycine (Neonotonia wightii cv. Tinaroo), guinea grass (Panicum maximum cvs Common, Hamil), creeping guinea (cv. Embu), para (Brachiaria mutica) and Koronivia (Brachiaria humidicola), with local legumes hetero (Desmodium heterophyllum) and Desmodium canum. Evans et al. (1992) note that Signal, sabi grass (Urochloa mosambicensis) and Koronivia will perform well under coconuts provided at least 70 percent of sunlight reaches the ground - an average situation for a good stand of 60 year old coconuts. “Given very careful management involving undergrazing, these grasses will probably persist down to 50 percent sunlight conditions. For replanted coconuts and particularly the hybrids at the recommended spacing of 9 m triangular, light conditions will be below 50 percent from 5–40 years of age. Under such conditions buffalo grass is the best available option at present, which combines high tolerance of shade and a growth habit which is resistant to overgrazing”. They note that although batiki blue grass has persisted at 50 percent light transmission levels under grazing at correct stocking rates in Solomon Islands and Western Samoa, it is better adapted to acid soils which are not widespread in Vanuatu.

In summarizing some of the work in Vanuatu, MacFarlane (1993) stresses that in open or lightly shaded situations receiving greater than 2,000 mm rainfall per year, with soils of greater than 0.5 m depth, in rehabilitation of gross weed infestation the Vanuatu Pasture Improvement Project has encouraged smallholders to vegetatively plant Koronivia grass (Brachiaria humidicola) or Signal grass (Brachiaria decumbens) with legumes hetero (Desmodium heterophyllum) and Vigna hosei and with seed of centro (Centrosema pubescens), and Glenn joint vetch (Aeschynomene americana). A growing number of commercial smallholders along with most plantations are now opting for full seeding of grasses and legumes. Locally produced siratro (Macroptilium atropurpureum) and glycine (Neonotonia wightii cvs Cooper and Tinaroo) are occasionally being used. New vegetatively propagated legumes such as Arachis pintoi and A. repens have been encouraged. Where farmers wish to improve carpet grass (Axonopus compressus) pastures, Koronivia or Signal grass are recommended with the normal legumes. Where farmers wish to improve unpalatable T-grass (Paspalum conjugatum) native pastures then the establishment of Signal grass with the above legumes is recommended as it gains height over T-grass more readily than Koronivia and will eventually smother out the native grass.

According to Evans et al. (1992) the tolerance of the commonly available climbing smothering legumes to increasing shade is as follows: siratro < glycine < greenleaf desmodium < centro < puero < calopo. For creeping legumes under moderate to heavy grazing the tolerance is: Indigofera spicata < Shaw vigna < Vigna hoseii, Teramnus < hetero, Arachis pintoi, Arachis repens, Desmodium ovalifolium. It was also noted that the production of a range of smothering and creeping legumes under 40 percent light transmission under coconuts is in progress at IRHO in Vanuatu.

Species performing well under coconuts in Tonga were B. decumbens, P. maximum, Centrosema pubescens and Leucaena (Powell, 1982).

In Serdang, Malaysia the screening of pasture species tolerant to shading was initiated inside a glasshouse (Hassan Wahab and Izham Ahmad, 1984). Fourteen species of legumes were evaluated under four different degrees of shade (100, 56, 34 and 18 percent sunlight). Calopogonium mucunoides, Calopogonium caeruleum, Centrosema pubescens, Desmodium ovalifolium and Pueraria phaseoloides showed a marked tolerance to shade even with only 18 percent sunlight. These are, in fact, common cover crops in rubber and oil palm plantations (Broughton, 1976; Han and Chew, 1981; MARDI, 1980; Watson et al. 1964). Under field conditions, the cumulative dry matter yields of these legumes (harvested at intervals of 10 and 15 weeks) declined with increasing shade, except in the case of Calopogonium caeruleum and Desmodium ovalifolium which gave higher production under reduced light than in full sunlight (MARDI, 1980).

Wong et al. (1985b) noted that the overall mean cumulative DM yields at 100, 56, 34 and 18 percent sunlight were 36.5, 25.7, 16.5 and 10.6 g pot^-1 respectively giving an average reduction of 30, 55 and 71 percent of DM yield for a corresponding reduction of 44, 66 and 82 percent photosynthetic quantum flux. A positive linear relationship between DM yield and light reduction was obtained for most of the legumes except for Calopogonium mucunoides, Desmodium ovalifolium and Calapogonium caeruleum which had optimum yield projected at 57 percent sunlight. Wong et al. (1985b) reporting on the complete trial ranked the legumes with the highest DM yields across all shade levels as follows (in descending order): Calopogonium mucunoides, Pueraria phaseoloides, Calopogonium caeruleum, Desmodium ovalifolium, Centrosema pubescens and Alysicarpus vaginalis. Stylosanthes guianensis cv. Endeavour cv. Schofield and Stylosanthes hamata cv. Verano grew poorly under heavy shade and Aeschynomene falcata, Desmodium triflorum, Leucaena leucocephala and Zornia diphylla were the lowest yielders at all shade levels.

On the basis of a number (10) of agronomic attributes such as DM yield, regrowth vigour, total leaf area, root dry weight, root/shoot ratio etc., Wong et al. (1985a) prepared an overall shade tolerance ranking (see Table 42). It was concluded that shade-tolerant species may not necessarily be high yielding, but moderate production on a long-term basis with high persistence under shade situations may be the most desirable qualities.

Wong et al. (1985a) also reported on the shade tolerance potential of twelve tropical grasses which were evaluated under artificial shade in greenhouse conditions (64, 30, 18 and 9 percent of full sunlight) and six selected grasses in a field experiment under light transmission of 100, 60, 34 and 18 percent and defoliated at six and ten-weekly intervals. “In the greenhouse trial, shading significantly (P<0.01) reduced tiller production, cumulative dry matter yields of shoot, leaf, stem, stubble and root, but enhanced specific leaf area. Increased partitioning of dry matter to the leaf component at the expense of root under shade resulted in higher shoot/root and leaf/stem ratios. Mean dry matter yield reduction across the grasses were 28.7%, 63.3% and 82.4% of that of the control. The best shade-tolerant grasses were Panicum maximum, P. maximum cv. Tanganyika, Digitaria setivalva and Brachiaria decumbens. The least shade-tolerant species were Setaria sphacelata cv. Kazungula, Digitaria decumbens cv. Transvala and B. ruziziensis. However, at dense shade, the indigenous grasses, Paspalum conjugatum and Axonopus compressus were ranked seventh and fourth respectively (see Table 43).

In the field experiment, P. maximum and B. decumbens were the best yielders across all shade levels. Mean dry matter yield reduction of the six grasses was 23.1% and 37.6% of the control for a 66% and 82% reduction in full sunlight. Axonopus compressus and P. maximum var. trichoglume produced higher DM at moderate shade under both defoliation intervals. The ten-weekly cut gave higher DM yield and tiller production under shade in the erect grasses, while the six-weekly cut resulted in higher yield for the prostrate grasses, viz. A. compressus and P. conjugatum.

Prolonged cutting intervals were preferred under heavy shade to enhance survival of the sown grasses. The nitrogen content of the grasses generally increased with shading and under shorter cutting interval. Low-yielding grasses, namely S. sphacelata cv. Kazungula and A. compressus, had higher nitrogen contents while P. maximum var. trichoglume had the lowest (Wong et al., 1985b).”

The results indicate that exotic grasses such as Panicum sp. and B. decumbens have maximum potential for forage production during the first five or six years in oil palm and rubber and in coconut until light transmission levels drop to between 50-30 percent of full sunlight. Below this light level indigenous grasses such as Axonopus compressus and Paspalum conjugatum are likely to take over through weed invasion.

In his review of forage screening and evaluation in Malaysia, Wong (1989) indicates that for low light levels (<50% sunlight) in plantations, the shade tolerant species P. conjugatum, A. compressus, C. pubescens and D. ovalifolium appear to be best. In moderate shade P. maximum and B. decumbens are suitable with dry matter yields of 5–7 t ha^-1 year^-1. In old coconut plantations, species suited to open conditions perform well: (P. maximum, P. purpureum, B. decumbens, S. sphacelata cv. Kazungula and MARDI digit (D. setivalva), while on Bris soils D. pentzii, D. decumbens, B. humidicola/dictyoneura, Zornia diphylla and Stylosanthes guianensis are promising.

Table 42. - Tropical legumes ranked for mean performance on 10 agronomic attributes under shading (After Wong et al., 1985b)

Ranking: 1 = best and 14 = worst
SLA = Specific Leaf Area

Table 43. - Ranking of twelve tropical grasses grown under four shade levels under greenhouse environment for overall shade tolerance based on the mean rank score of nine agronomic attributes (after Wong et al., 1985a)

Ranking: 1 = best; 12 = worst.

Chen and Hashim (1984) assessed the effect of frequency of defoliation (12 and 16 weeks) on six grasses on Bris soils. Dry matter production ranging from 6,128 to 11,530 kg ha^-1 year^-1 was considerably higher than for native species dominated by Zoysia matrella at 1,698 kg ha^-1 year^-1 and longer cutting interval led to sustained production. However, Digitaria pentzii produced best when defoliated every three months. Wong et al. (1988) carried out a grazing assessment of D. pentzii, D. decumbens, P. maximum, B. decumbens, Cynodon plectostachyus and Zoysia matrella with goats under 18 year old coconut palms on Bris soils. Average dry matter yield was highest for B. decumbens followed by P. maximum and D. pentzii, but all introduced grasses showed poor persistence, which is probably not surprising as light transmission under the 18 year old coconuts was only 33 percent. Naivasha star grass (Cynodon plectostachyus) ranked the lowest while the indigenous grass Zoysia matrella was the most persistent under grazing by goats. Ahmad et al. (1981) noted that Verano stylo established better than Schofield stylo and Desmodium ovalifolium under the Bris soils.

In a two-year study under the fully closed canopy of oil palm (6–16 percent mean light transmission) Chen and Bong (1983) evaluated 16 grasses for dry matter production, persistence and chemical composition. In general yields were 90 percent lower compared to the same grasses grown in the open (as reported by Wong, 1980). The highest yield was from Brachiaria decumbens (1727 kg ha^-1 yr^-1) followed by Brachiaria brizantha (1235 kg ha^-1 yr^-1), Paspalum conjugatum (1145 kg ha^-1 yr^-1), Panicum maximum (1029 kg ha^-1 yr^-1), Digitaria setivalva (1007 kg ha^-1 yr^-1) and Axonopus compressus (929 kg ha^-1 yr^-1). Improved grasses were less persistent than the native species (Paspalum conjugatum and Axonopus compressus). Grazing experiments conducted under similar shade conditions in oil palm confirmed the persistence of A. compressus and P. conjugatum (Chen et al., 1978). Chen and Bong (1983) ranked (in descending order) the persistence of grasses under oil palm shade in the following sequence: A. compressus, P. conjugatum, Dichanthium aristatum, B. decumbens, B. brizantha, Digitaria decumbens, P. maximum, P. maximum cv. Tanganyika, S. spacelata cv. Kazungula, P. maximum var. trichoglume, Paspalum plicatulum cv. Bryan, Cynodon plectostachyus and P. plicatulum cv. Rodd's Bay.

Of the 8 legumes tested under the same conditions (Chen and Othman, 1984), the highest dry matter yield was produced by Desmodium ovalifolium (1970 kg ha^-1 yr^-1). Although Calopogonium caeruleum and Centrosema pubescens could tolerate shading, their dry matter production was relatively low. D. heterophyllum and S. guianensis cv. Endeavour and Cook produced negligible yields while C. mucunoides and M. atropurpureum cv. Siratro deteriorated immediately after sward establishment. (See Table 44). It was noted that there was a strong correlation between root dry weight and plant survival (r = 0.80). The overall dry matter production of all legumes was low, compared to their production in full sunlight (Wong et al., 1982) and declined over time as the canopy closed. The best species, D. ovalifolium, maintained only 40 percent of its relative yield in the open, whereas the second ranking species C. caeruleum and C. pubescens sustained only 10 and 15 percent respectively of their relative yields. The remaining species produced negligible yields under such a low light environment.

Although it has been suggested that prostrate grasses should be able to persist better at low light levels under frequent defoliation than erect grasses, Wong and Stur (1993), comparing the prostrate Paspalum wettsteinii and the erect Paspalum malacophyllum, concluded that at least for P. wettsteinii the prostrate growth habit did not increase persistence in shade. Although producing a similar total biomass, P. wettsteinii has a higher root yield, while P. malacophyllum had a larger shoot component and the survival of P. wettsteinii was significantly lower. The poor persistence of P. wettsteinii was related to a lower total non-structural carbohydrate content of stubble and lower tillering ability and regrowth potential.

Ahmad and Wahab (1983) tested six improved grasses and the shrub legume Leucaena leucocephala at a farmer's field site in Jasin, Malaysia in 1981 and 1982. The site was shaded by rubber and fruit trees and had a light transmission value of 68 percent of full sunlight. Panicum maximum and Pennisetum purpureum were the top yielders and with leucaena would appear to be the best species for cut-and-carry systems (see Table 45). Surprisingly, B. decumbens yielded poorly and it is noted that the yield of B. mutica (which is not a shade tolerant species) declined markedly in the second year of cutting.

In Western Samoa, Reynolds (1978f and 1978) rated a number of grasses in a coconut shaded environment with 60 percent light transmission on the basis of yield, animal preference and sixteen selected characteristics. Details of forage dry matter production are given in Table 46 and species are classified on the basis of level of production into four groups. Both D. decumbens and B. mutica demonstrate very low shade tolerance. Dry matter production was shown to be seasonal with growth rates in the dry season approximately half those in the wet season. In Table 47, species are rated in terms of sixteen characteristics identified as being particularly relevant to Western Samoa and the Pacific region. The top six species were B. dictyoneura, B. miliiformis, I. aristatum, B. brizantha, P. maximum cv. Embu and B. decumbens. Suggestions for accompanying legumes included C. pubescens, M. atropurpureum, P. phaseoloides, D. heterophyllum and L. leucocephala.

Based on yield under shade (as a percent of unshaded yield) Ludlow (1980) ranked shade tolerance of species in decreasing order: grasses - B. miliiformis, B. brizantha, P. clandestinum, P. maximum, D. decumbens and P. purpureum; legumes - D. intortum, C. pubescens, N. wightii, D. canum, L. leucocephala, M. atropurpureum and S. guianensis. Sillar (1967) showed that reduction in light intensity to 74 percent daylight caused a marked decrease in both top dry matter (47 percent decrease) and root dry matter (44 percent decrease) production of S. humilis. At lower light levels yields were very low demonstrating the degree of sensitivity of S. humilis to shade.

Table 44. - The agronomic characters and performance of tropical legumes under oil palm canopy (after Chen and Othman, 1984)

* Log x transformed;
** Log (x + 1) transformed;
Parenthesis - actual data
a, b, c, d = means with different superscripts in the same column are significantly different from each other (P<0.05)

Table 45. - Dry matter production of grasses and leucaena at Jasin, Malaysia (after Ahmad and Wahab, 1983)

* Figures in bracket for leucaena refer to proportion of leaf in the total yield.