Table 46. - Annual dry matter yield data grouped on the basis of level of production for grass species grown under coconuts. Light transmission, 60%, Western Samoa (Reynolds, 1978f).
|Group Production Level||Yield range (kg ha-1)||Name||Dry matter Production (kg ha-1)*|
|A - very high||14–16,000||P. maximum Tall guinea, var. B||15887a|
|P. maximum Tall guinea, var. A||14128a|
|B - high||10–14,000||P. maximum cv. Embu Creeping guinea||10597b|
|B. humidicola Koronivia||10540b|
|C - medium||7,500–10,000||P. plicatulum Paspalum||9678bc|
|B. brizantha Palisade||8871bcd|
|P. purpureum Napier-hybrid||8596bcde|
|P. maximum Guinea||8589bcde|
|P. conjugatum Tee grass||8578bcde|
|P. maximum var. trichoglume Green panic||8459bcde|
|B. miliiformis Cori||8209cde|
|I. aristatum Batiki||8021cde|
|P. purpureum Napier-local||7873cdef|
|D - low||<7,500||D. decumbens Pangola (weeds)||7295def|
|B. mutica Para||6752ef|
* Mean values with one or more common letter(s) are not significantly different at the 5% level (Duncan's New Multiple Range Test).
One of the most detailed evaluations of tropical grasses under increasing coconut shade was carried out in the Solomon Islands by Smith and Whiteman (1983a). The yields of eight grass species: A. compressus, B. decumbens, B. humidicola, B. miliiformis, D. caricosum, I. aristatum, P. conjugatum and S. secundatum, were compared under coconuts giving light transmission values of 100 (open sites), 70, 50, 40 and 20 percent of full sunlight. Total dry matter yields were greatest in full sunlight and declined with increasing shade (see Table 48 and Figure 38). The three Brachiaria species yielded the most in full sunlight followed by I. aristatum and D. caricosum. At 70 percent light transmission B. decumbens and B. humidicola were best followed by B. miliiformis, I. aristatum and D. caricosum. I. aristatum maintained its yield at 50 percent light transmission and joined B. decumbens and B. humidicola as the most productive. As shade deepened (40 percent light transmission) there was a marked change of order so that I. aristatum, S. secundatum and B. decumbens represented the largest yielding group. Yields were very low under intense shading (20 percent light transmission) with S. secundatum the most productive while weed percentages considerably increased. B. decumbens (Signal) and B. humidicola (Koronivia) were recommended for open plantations (light transmission > 70 percent), I. aristatum (Batiki Blue) for moderate shade (45–70 percent light transmission) and S. secundatum (Buffalo couch or St. Augustine grass) for more intense shade (30–50 percent light transmission).
Stur and Shelton (1991a) in reviewing available forage resources in plantations in Southeast Asia and the Pacific summarized their main characteristics including their shade tolerance and potential competition with plantation crops (see Table 49).
Hacker and Williams (1993) in reviewing selected herbaceous and shrub legumes and pasture grasses for the South Pacific Region and some aspects of their adaptation listed the following as most shade tolerant: Arachis pintoi, Desmodium heterophyllum, D. heterocarpon, D. ovalifolium, Vigna hosei, Panicum maximum var. trichoglume and Stenotaphrum secundatum.
Chen (1991) has summarized the dry matter productivity of the main tropical forage species under different light regimes of different tree crop canopies. These are shown in Table 50 and the dramatic decline in dry matter productivity with increased shade (decreased light transmission) is apparent under coconut, rubber and oil palm.
Although there have been a number of studies on the shade tolerance of herbaceous legumes (e.g., Eriksen and Whitney, 1982; Kaligis and Sumolang, 1991; Ng, 1991; Rika et al., 1991; Stur, 1991; Wong, 1991; Wong et al., 1985b) less information is available on tree legumes. Egara and Jones (1977) showed Leucaena leucocephala to have limited shade tolerance but more detailed studies have only been undertaken recently under the ACIAR Forage Program (No. 8560). Benjamin et al. (1991) reported on the response of six fodder tree legumes to a range of light intensities ranging from 100, 70, 50, 30 to 20% of incident light transmission inside a glasshouse (in Australia). The glasshouse itself reduced incident light of all treatments by about 30%. Dry matter yields are shown in Figure 34 and the results were described in Chapter 2 where the relative order of shade tolerance was Gliricidia sepium > Calliandra calothyrsus > Leucaena leucocephala > Sesbania grandiflora > Acacia villosa > Albizia chinensis.
Tree legumes have been used as a traditional fodder source for ruminants in Bali. They have also been used as supports and to provide shade for vanilla and pepper. With the psyllid insect causing serious damage to Leucaena leucocephala other psyllid-resistant tree legumes are required. Oka Nurjaya et al. (1991) reported on a trial under coconuts (58% light transmission) to identify suitably adapted species. Details of accumulated leaf, stem and total dry weight over six harvests and mean leaf percentage are shown in Table 51.
It was concluded that Calliandra calothyrsus, Codariocalyx gyroides, Desmodium rensonii and Gliricidia sepium warrant further study as forage species for use in coconut plantations in Bali.
Table 47. - Rating of grass species for grazing in coconut areas1 (Reynolds, 1978l)
|P. purpureum (napier)||2||3||3||5||2||5||2||1||4||5||4||5||1||5||2||3||3.3||9=|
|B. mutica (para)||5||4||4||4||1||1||3||2||2||5||2||5||2||4||1||5||3.1||73|
|B. miliiformis (Cori)||3||3||1||3||2||2||3||2||2||2||2||3||2||2||1||2||2.2||1 =|
|B. brizantha (palisade)||3||1||2||3||2||2||3||3||3||2||2||3||2||3||1||2||2.3||4|
|P. maximum cv. Embu (creeping guinea)||2||2||2||3||2||2||2||3||3||3||2||3||2||3.5||1||2||2.3||5|
|B. humidicola (Koronivia)||2||2||1||2||3||3||3||3||3||2||3||1||2||2||1||2||2.2||1 =|
|P. maximum var. trichoglume (green panic)||3||3||3||3||4||5||2||3||3||4||5||1||2||3.5||5||2||3.4||11|
|P. maximum (guinea)||2||3||2||4||4||5||1||4||5||3||5||4||2||4||5||2||3.4||12|
|I. aristatum (batiki)||3.5||2||1||2||2||2||4||4||1||1||1||1||3||2||1||3||2.5||3|
|P. maximum (tall guinea)||1||3||2||5||2||3||1||4||5||4||5||4||2||5||3||2||3.3||9 =|
|B. decumbens (Signal)||3||1||2||3||3||2||3||3||3||2||3||3||2||3||1||2||2.6||6|
|D. decumbens (pangola)||5||5||5||3||3||3||3||2||3||3||3||5||1||3.5||1||5||3.3||83|
Notes: 1 - Grass with lowest mean score is rated most acceptable species
2 - Characteristics:
A - forage production class
B - ability to compete with weeds
C - shade tolerance
D - height of sward
E - establishment ability
F - ability to spread quickly
G - tolerance of drought
H - animal preference
I - probable competition with coconuts
J - ability to stand heavy grazing
K - ability to establish from cuttings
L - ability to tolerate low management levels
M - ability to respond to fertilizer use
N - ease of locating coconuts
O - probable cost of seeds/planting material
P - animal performance
3 - Even though pangola and para rate better than guinea, their very low shade tolerance makes them unsuitable for the average shaded coconut site.
Table 48. - Total above-ground dry matter (DM, t ha-1) and yield of sown species (t ha-1) over six harvests at each light transmission site, and correlation coefficients (r) between light transmission (%) measured with the integrating pyranometer and yields of sown species (Smith and Whiteman, 1983a)
|Species||Above-ground DM yields (t ha-1)|
|B. decumbens (Signal)||28.2||28.0||12.7||11.0||10.9||9.3||6.1||4.1||3.3||0.7||0.95++|
|B. humidicola (Koronivia)||22.8||21.9||13.6||12.4||11.1||9.8||4.7||1.7||2.6||0.7||0.99++|
|B. miliiformis (Cori)||18.1||17.8||7.1||9.8||7.4||4.4||5.7||3.4||3.3||1.0||0.99++|
|I. aristatum (Batiki blue)||15.3||14.0||8.3||7.8||8.9||8.3||6.7||5.5||3.1||0.3||0.86++|
|D. caricosum (Nadi blue)||14.3||12.8||7.0||4.7||6.9||3.8||3.9||1.8||3.3||0.3||0.93++|
|P. conjugatum (Tee grass)||11.4||7.8||5.9||2.0||4.3||1.9||4.7||2.6||2.6||1.0||0.56(NS)|
|A. compressus (Mat grass)||9.3||4.6||6.4||4.4||6.1||4.9||3.7||1.9||3.1||1.3||0.70+|
|S. secundatum (Buffalo couch)||7.0||5.5||6.5||3.5||6.0||4.0||5.7||4.9||3.3||1.9||0.64+|
|Mean yield as a % of site A||100||100||56||47||49||40||33||23||20||6|
|LSD||spp. × sites||Total||sown|
* Correlation coefficients significant at P = 0.01 (++), P = 0.05 (+), or not significant (NS).
Table 49. - Summary of adaptation of frequently occurring forages (after Stur and Shelton, 1991a)
|Tolerance to shade||Forage yield||Animal product.||Required||Resistance to||Fertilizer response||Potential competition with plantation crops|
|Management level||Soil fertility||Grazing||Drought||Soil acidity||Water logging||Weed invasion|
|Sown or planted|
L = low;
M = moderate;
H = high.
Table 50. - Productivity (DM t ha-1 year-1) of some tropical forages in pure swards grown under the natural shade of plantation crops (after Chen, 1991; Wong 1991)
|Species||Shade as % of sunlight||Reference|
|Brachiaria decumbens||0.7||4.4||9–11||28||Smith and Whiteman (1983a)|
|Stylosanthes guianensis||-||-||-||15.2||Steel and Humphreys (1974)|
|Panicum maximum (tall)||-||-||15.0||-||Reynolds (1978f)|
|Panicum maximum cv. Embu||-||-||10.6||-|
|Brachiaria brizantha||-||-||5–11||-||Manidool (1984)1|
|Brachiaria miliiformis||1.2||4.3||8.4||8.8||Waidyanatha et al. (1984)|
|Panicum maximum||3.5||-||8.5||14.5||Najib (1989)|
|Panicum maximum||1.0||-||-||-||Chen and Bong (1983)|
|Desmodium ovalifolium||2.0||-||-||-||Chen and Othman (1984)|
Table 51. - Total accumulated dry weight (g tree-1) of tree legumes in Bali (after Oka Nurjaya et al., 1991)
|Species||Leaf DW||Stem DW||Total DW||Leaf|
|Desmodium rensonii CPI 76099||598||564||1162||51|
|Calliandra sp. CPI 108458||571||243||814||70|
|Gliricidia sepium (local) Bali||514||279||793||65|
|Codariocalyx gyroides CPI 49082||415||327||742||56|
|Desmodium salicifolium CPI 70257||323||229||552||59|
|Desmodium distortum CPI 28324||297||259||556||53|
|Flemingia macrophylla CPI 100793||296||122||418||71|
|Erythrina sp. (local) Bali||193||95||288||67|
|Leucaena diversifolia CPI 46568||166||128||294||57|
|Sesbania grandiflora (local) Bali||127||88||215||59|
|Desmodium discolor CPI 39075||119||112||231||52|
|Sesbania sesban (local) Bali||75||92||167||45|
|Leucaena pallida CPI 91309||75||49||124||61|
|Leucaena diversifolia CPI 46568||59||51||110||53|
|Leucaena leucocephala cv. Cunningham||38||13||51||74|
|Pseudarthria hookeri CPI 70286||34||17||51||66|
A similar study was carried out in North Sulawesi where Gliricidia sepium and Erythrina sp. are commonly used as fences and live stakes under coconuts (Kaligis et al., 1991). Nine introduced and four local species were evaluated over the period December 1988 to June 1990 during which time nine harvests were taken. Calliandra sp. CPI 108458 produced by far the highest leaf yields and other potentially useful species included Flemingia macrophylla, Calliandra calothyrsus (local), Gliricidia sepium (local), Desmodium rensonii and Codaricalyx gyroides. In the drier environment of South Sulawesi Ella et al. (1980) had earlier found little difference between the leaf yield of C. calothyrsus, L. leucocephala and G. sepium. This was before the effect of psyllid on Leucaena.
Although grass species like Napier (P. purpureum), tall and common Guinea (P. maximum) perform well under moderate coconut shade, in general they are too aggressive, competing with coconut palms for moisture and nutrients; their erect growth habit makes location of fallen nuts difficult. Thus they are not generally recommended as grazing species but may have an important role to play in smallholder schemes where stall feeding and cut-and-carry systems are operated (Humphreys, 1978; Iniguez and Sanchez, 1991; see 5.3.11). In Sri Lanka Setaria sphacelata was also considered as a fodder species (Liyanage, 1986) However, where adequate fertilizer is used common guinea is successfully grown under coconuts (McEvoy, 1974; Reynolds, 1981). Shade tolerance ratings for some grass and legume species have been listed by Humphreys (1981) and are shown in Tables 42, 43, 47, 49 and 52.
Grass species best suited to reduced light conditions under coconut palms are sod forming stoloniferous grasses that form short to moderate height swards (see Figure 51). They provide moderate carrying capacity, allow fallen nuts to be quickly located, are inexpensive and easy to establish from cuttings, compete well with aggressive weed species, maintain a reasonable balance with companion legumes under grazing and do not compete excessively with coconut production. Such grasses include Angleton grass or Alabang X (D. aristatum), Batiki blue (I. aristatum), Cori (B. miliiformis), Koronovia (B. humidicola), Palisade (B. brizantha), Signal (B. decumbens) and possibly Creeping Guinea (P. maximum cv. Embu). Although Para grass (B. mutica) is popular in the Philippines, Moog and Faylon (1991), experience in the Solomon Islands (Watson and Whiteman, 1981a), Thailand (Boonklinkjorn, 1978) and Western Samoa (Reynolds, 1978f) has shown that is not very shade tolerant and requires good management to persist under the high light conditions (light transmission > 75 percent) of old coconut plantations (trees 50–60 years old) or where coconuts have been widely spaced (9–10 m2). Other grasses reported to perform well in more open coconut plantations include Digitaria setivalva and Setaria splendida and Urochloa mosambicensis in drier areas. Various Paspalum species such as P. notatum and P. wettsteinii are also being evaluated for shade tolerance and persistence.
Figure 51. - Cattle grazing on B. miliiformis pastures under coconuts, Western Samoa.
Although Pangola grass (D. decumbens) has been used under coconuts in Jamaica (Anon, 1971a) it was very intolerant of shade in Western Samoa (Reynolds, 1978f). Surprisingly in trials in Brazil (Schreiner, 1987) yields of D. decumbens were similar to those of B. decumbens under heavy shade. In the Solomon Islands, Smith and Whiteman (1983a) noted that Cori grass produced most of its yield in the first six months and died back after flowering. Bogdan (1977), in fact, records B. miliiformis as an annual species, suggesting that Cori grass is better adapted to monsoonal environments as found in Sri Lanka rather than the humid tropics of the Solomons. It was noted in the Solomons that Cori and Creeping Guinea were both susceptible to insect (grasshopper) damage (Steel and Whiteman, 1980).
Buffalo couch or St. Augustine grass (S. secundatum) is the most important grass under coconuts on low fertility soils in Vanuatu in the South Pacific (Macfarlane and Shelton, 1986; Weightman, 1977), while in Zanzibar and in other coastal areas of East Africa Pemba grass (S. dimidiatum) is widespread. Although producing only low dry matter yields, both species appear to be well adapted to conditions of heavy shade outyielding those species which are more suited to plantations where light transmission is in excess of about 40 or 50 percent. Species such as mat grass (A. affinus and A. compressus) are also widespread under these heavily shaded conditions. Beetle (1974) reviewing P. conjugatum suggests that because of its shade tolerance and aggressive nature Tee grass or sour paspalum makes a natural and uniform cover in a range of tropical plantations such as rubber and coconut. In fact, A. compressus and P. conjugatum are probably the most common natural forage species found in coconut, rubber and oil palm plantations. In Malaysia, the weed Asystasia intrusa performed so well under heavy shade that perhaps its role in shady conditions should be re-examined (Burns et al., 1993). Zoysia matrella was also persistent under grazing (Wong et al., 1988).
In establishing pastures the degree of shade will determine which of the recommended grass species is most suitable (see Table 52). Where light transmission is <30 percent, dry matter yields of all species are low so that grazing of existing species (such as A. compressus) may be most appropriate. Smith and Whiteman (1980) and Smith et al. (1981) concluded after a number of trials, that sown pastures cannot persist under heavy shade in a grazed situation.
Therefore, under low light conditions “where Axonopus is already established, there is little advantage in planting introduced species”. Smith et al. (1983) suggest that “the present recommended species should not be planted at sites with less than 60 percent light transmission”. In open plantations (light transmission > 75 percent) the choice of species is wide but B. brizantha, B. decumbens and B. humidicola are particularly recommended. In more shady conditions (light transmission 50–75 percent) I. aristatum and B. humidicola should be used, while in heavier shade (light transmission 30–50 percent) I. aristatum may be suitable, but species such as S. dimidiatum and S. secundatum are probably most appropriate.
The legumes most suited to coconut plantations include centro (C. pubescens) and Siratro (M. atropurpureum), with puero (P. phaseoloides) and sometimes Calopo (C. mucunoides) used as pioneers (and as cover crops). However, in some humid tropical environments Siratro is subject to Rhizoctonia leaf blight (Reynolds, 1983). Recent work has identified Arachis pintoi cv. Amarillo (as well as other Arachis species) as one of the most promising legumes under shade. It has also persisted under heavy grazing, but further work is needed. In Vanuatu, glycine (Neonotonia wightii) has combined well with signal grass under shade. Legumes that combine particularly well with B. brizantha and B. decumbens include D. canum, hetero (D. heterophyllum), D. triflorum and alyce clover (A. vaginalis). Sensitive plant (M. pudica) should be utilized where indigenous, but it needs to be carefully controlled. Vigna (V. luteola) may be a useful pioneer legume but appears to decline quickly under sustained grazing or cutting, and during dry periods (Reynolds, 1982c). Other useful legumes include S. guianensis and in Zanzibar T. labialis was found to associate well with Pemba grass (S. dimidiatum). Leucaena (L. leucocephala), or (on acid soils) gliricidia (G. sepium/maculata), can be grown as a double-row hedge (rows 1 m apart) between every two rows of coconuts and a number of tree legumes such as Calliandra calothyrsus warrant further study.
Table 52. - Recommended grass species for different light conditions
|Light transmission (%)|
|Establishment not generally recommended.|
Graze existing species.
|I. aristatum||B. brizantha||B. brizantha +|
|S. dimidiatum +||B. decumbens||B. decumbens +|
|S. secundatum||B. humidicola +||B. humidicola +|
|A. compressus||I. aristatum +||B. miliiformis|
|P. maximum cv. Embu|
|I. aristatum (B. mutica) ++|
+ Especially recommended
++ Only suitable in very open plantations with high light transmission.
Other legumes being evaluated in Vanuatu and Western Samoa include Aeschynomene americana cv. Glenn (Glenn Joint Vetch) - very tolerant of heavy grazing (however, Kolmbacher and Martin, 1983, noted that 45 percent incident light was the minimum light level for good joint vetch establishment), Arachis repens (shade tolerant and very tolerant of heavy grazing - Evans et al., 1992), Cassia rotundifolia cv. Wynn (Wynn Cassia), Centrosema pascuorum cv. Cavalcade (Bundey centro or Centurion) and Vigna hosei and parkeri. However, it is too soon to make recommendations for their use under coconuts and several appear to have low shade tolerance.
At a workshop in Medan, North Sumatra, Indonesia in September 1990, (Iniguez and Sanchez, 1991) a Working Group, after reviewing past evaluations of germplasm, recommended various species as a starting point for future evaluations of shade tolerant, productive and persistent species (see Table 53).
Table 53. - Potential candidate forage material1 for integrated tree cropping and small ruminant production systems (after Iniguez and Sanchez, 1991)
|Crop and Age|
|Young rubber/oil palm|
|3–6 yr rubber/oil palm|
|Light Transmission (%)|
|Brachiaria decumbens3||Arachis sp.||Arachis sp.|
|Brachiaria humidicola||Desmodium ovalifolium||Stenotaphrum secundatum|
|Brachiaria mutica||Paspalum notatum|
|Digitaria setivalva (MARDI digit)||Paspalum wettsteinii|
|Pueraria phaseoloides||Axonopus compressus|
1 These were chosen on the basis of:
- productivity and compatibility with tree crops
- ability to perform under defined light regimes
- persistence under grazing, and
- absence of adverse animal effects.
2 For cut-and-carry systems pure stands of Pennisetum purpureum, Tripsacum laxum and tree legumes were recommended.
3 Can cause photosensitization in sheep.
Recently, the ACIAR funded project “Integration of Forages with Plantation Crops for Sustainable Ruminant Production” (MacFarlane et al., 1994) identified the following species for grazing under coconuts:
Grasses - Brachiaria humidicola, Stenotaphrum secundatum, Brachiaria decumbens
grown in mixture with:
Legumes - Arachis pintoi, Arachis repens, Arachis glabrata, Desmodium heterophyllum.
Species with a similar growth habit which may also be suitable include Brachiaria brizantha, Ischaemum aristatum, Stenotraphrum dimidiatum.
According to Wilson (1991) the majority of tropical grasses and legumes currently in use (and in genetic stocks) have never been specifically collected from shaded habitats or evaluated for shade performance. In terms of species for the plantation environment the number of forage genotypes so far evaluated is minute in relation to the genetic resources available. However, he suggests that shade tolerance should not be related directly to productivity performance under low light and also that as light levels change dramatically under rubber and oil palm in the first 5 years, true shade species may not survive in the first three or four years when plantation light levels are high. Under coconuts light levels are more stable over a large number of years and are at a moderately high level (50– 80 percent sunlight) so that true shade species are not required. In this case the species selected may need a moderate level of shade adaption, but possibly other agronomic features such as tolerance to grazing and low growing habit (for coconut collection) may be relatively more important.
Recent species screening work is covered in Chapter 10.
A factor which may have an important bearing on the selection of grass and legume species is the level of management and the simplicity/complexity of the proposed system (see Table 54). A grass such as B. miliiformis with centro, regularly fertilized may give excellent yields with a well managed dairy herd under light transmission conditions of about 75–80 percent. Where beef steers are being grazed on the same area with low inputs and minimal levels of management the more appropriate species may be I. aristatum, S. dimidiatum or possibly B. humidicola with D. heterophyllum, A. vaginalis or T. labialis. Lack of persistence of grass species and invasion by unpalatable, broadleaf weeds have been reported as key management problems in coconut plantations (Shelton et al., 1987a; Rika et al., 1981; Smith and Whiteman, 1985; Watson and Whiteman, 1981a). Unpalatable weed invasion is a major problem in overgrazed smallholder pastures under coconuts (Shelton et al., 1986) and Shelton (1991) suggests that at least for the South Pacific Region future research should aim to provide simple and robust systems suitable for indigenous smallholders with only recent experience of pasture and cattle management.
Where particular soil characteristics occur the choice of species may be very limited. Thus in the Solomon Islands, Koronivia (B. humidicola) was the only grass to perform well on coastal coralline sands at Lever Point where most of the species suffered from iron-chlorosis. Among legumes, only Siratro (M. atropurpureum) performed well in the same environment (Gutteridge and Whiteman, 1977b, 1978). In Fiji where I. aristatum and D. caricosum are the most commonly used grasses, they are replaced by P. maximum cv. Embu and M. atropurpeum on the recent Krasnozems of Taveuni and by a mixture of B. humidicola and M. atropurpureum on the coral sands at Vunilagi (Thompson, 1973; UNESCO, 1979).
The basis of adaptation to drought has been discussed in some detail by Humphreys (1981). While tall plants may assist in trapping rainfall and increasing rain water penetration into the soil (Glover et al., 1962), important characteristics are differences in the depth of active rooting (Burton et al., 1954), in root morphology, root-shot ratio (Taerum, 1970) as well as differences associated with the leaf surface such as leaf movements (Begg and Torssell, 1974), leaf-covering structures, control of leaf expansion and senescence and stomatal resistance.
Table 54. - Level of management for selected grasses and legume (Reynolds, 1980)
|Level of Management|
|A. compressus||B. humidicola||B. miliiformis|
|S. dimidiatum||B. brizantha||B. mutica|
|S. secundatum||B. decumbens||P. maximum cv. Embu|
|I. aristatum||I. aristatum||P. maximum|
|D. heterophyllum||P. phaseoloides||S. guianensis|
|A. vaginalis||C. pubescens||M. atropurpureum|
|T. labialis||L. leucocephala||C. pubescens|
Many coconut areas in the tropics have a pronounced dry season of variable length. Therefore it is important that the selected grass and legumes species have drought tolerance. Various agronomic characteristics, including tolerance to drought, pertaining to the main grasses and legumes have been summarized by Whiteman (1980) and Reynolds (1983). The latter also reported (1978d) on drought tolerance of species in Western Samoa. There the major contrast was between P. maximum (tall and common), leucaena (L. leucocephala) and Centro (C. pubescens) which remained green throughout very dry periods while species like Batiki Blue (I. aristatum), Calopo (C. mucunoides) and the local pastures (composed of A. compressus and weeds) browned off and died back (see Table 55). In Zanzibar, centro maintained good growth through the dry season on very shallow soils derived from limestone (Reynolds, personal observation).
Table 55. - Species drought tolerance in Western Samoa (Reynolds, 1978d)
|Degree of drought tolerance||Species|
|Very good||Tall guinea (P. maximum), Common guinea (P. maximum), leucaena (L. leucocephala), centro (C. pubescens).|
|Good||Creeping guinea (P. maximum cv. Embu),|
napier (P. purpureum), Koronivia (B. humidicola),
green panic (P. maximum var. trichoglume).
|Moderate||Palisade (B. brizantha), Cori (B. miliiformis),|
Puero (P. phaseoloides), Siratro (M. atropurpureum),
Para (B. mutica).
|Poor||Batiki Blue (I. aristatum), P. commersonii|
|Very poor||Calopo (C. mucunoides), Carpet or Mat grass (A. compressus).|
The ability to survive flash flooding or to grow in swampy and waterlogged areas may be important in some coconut areas (although these will be limited as coconuts usually grow best in well drained soils). Skerman and Riveros (1990) have reviewed and classified the various grasses while Javier (1983) investigated the effects of flooding on seven species of tropical pasture legumes (see Tables 56 and 57). Whiteman et al. (1981) found that waterlogging tolerance decreased in the following order: M. lathyroides > S. guianensis cv. Schofield > Siratro > C. pubescens cv. Common. Gilbert et al. (1992) confirmed that M. lathyroides cv. Murray grew best under waterlogged conditions; S. hamata cv. Verano, S. scabra cv. Seca, and S. scabra cv. Fitzroy were reasonably tolerant while M. atropurpureum cv. Siratro, C. schiedianum cv. Belalto, S. guianensis cv. Cook and S. hamata CPI 33205 were poor.
Wondimagegne Shiferaw et al. (1992) demonstrated that Aeschynomene americana cv. Glenn, Lotus pendunculatus cv. Maku and Trifolium semipilosum were tolerant of waterlogging while Medicago sativa and Vigna parkeri were intolerant. Halim and Hamid (1989) demonstrated that para grass (Brachiaria mutica) was the grass species most adapted to flooded conditions whereas guinea (Panicum maximum) and Signal (Brachiaria decumbens) were least tolerant with Setaria splendida relatively tolerant to short periods of flooding.
Grasses and legumes suitable for smallholder coconut environments include Axonopus affinis, Brachiaria humidicola, Dichanthium aristatum, Ischaemum indicum, Stenotaphrum secundatum, Calopogonium mucunoides, and Desmodium heterophyllum. Brachiaria mutica will only persist where light transmission values are in excess of 75 percent and management levels are good. According to Skerman (1977), Centrosema pubescens is fairly tolerant of flooding (better than Siratro (Macroptilium atropurpureum) but not as good as puero (Pueraria phaseoloides) and in the Philippines has survived stagnant water for at least 2 months (Farinas, 1966). Evans and MacFarlane (1990) note that Desmodium intortum is well adapted to poorly drained or waterlogged soils and Centrosema pascuorum cv. Cavalcade survives prolonged waterlogging and partial submersion in seasonal flooding.
Table 56. - Grasses suited to aquatic, semi-aquatic and moist areas (after Skerman and Riveros, 1990).
|Grass flourishing in perennial wet places (lakes, marshes, swamps)||Grass growing on the banks of perennial streams||Grasses growing in seasonally wet places|
|Acroceras macrum||Brachiaria mutica||Andropogon gayanus|
|Brachiaria mutica||Panicum repens||Axonopus affinis|
|Echinochloa crus-galli||Pennisetum purpureum||Brachiaria humidicola|
|Echinochloa pyramidalis||Phragmites australis||Brachiaria mutica|
|Hymenachne acutigluma||Saccharum spontaneum||Cynodon dactylon|
|Lecersia hexandra||Dichanthium aristatum|
|Vossia cuspidata||Dichanthium caricosum|
Table 57. - Relative tolerance to flooding of several tropical pasture legumes (Javier, 1983)
1 = highest relative tolerance 7 = lowest
Occasionally, pastures may need to be established in seashore areas which may be subject to salt spray. Of the shade tolerant grasses suited to the coconut environment Dichanthium aristatum and Stenotaphrum secundatum are the most salt tolerant (Skerman and Riveros, 1990) with Brachiaria mutica moderately salt tolerant (in the more open areas). One of the few legumes which can tolerate saline conditions is Vigna luteola (Hutton, 1968). Other legumes which can tolerate moderately saline conditions are Macroptilium atropurpureum, Stylosanthes humilis and Leucaena leucocephala (Skerman, 1977). However, Keating et al. (1986) indicated that M. lathyroides cv. Murray and Siratro are more tolerant of salinity than S. scabra and S. humilis. Parawan (1991) also includes P. maximum, P. purpureum, D. aristatum, C. gayana and C. pubescens as species able to tolerate salinity in coastal areas. Satjipanon (1994) mentions that Panicum coloratum var. makarikariense is both drought and salt tolerant.
Where grazing of beef or dairy animals on large commercial units is planned, sod or sward forming stoloniferous grasses and associated legumes are preferred. If the smallholder intends to stall feed using cut-and carry techniques, then napier (P. purpureum), guatemala (T. laxum), guinea (P. maximum) and possibly leucaena (L. leucocephala) are recommended. However, if a marked dry season is common then even on the large commercial units, areas of napier, leucaena and possibly sugarcane (Saccarum officinarum) or banana (Musa sapientum) may be established as emergency dry season feed.