A well-balanced greenleaf desmodium-Nandi setaria pasture (receiving 250 kg/ha/year single superphosphate and 60 kg/ha/year KCl), continuously grazed at 1.7 beasts per hectare, at the Samford Pasture Research Station near Brisbane.
Lot feeding is often considered the only efficient way to produce beef. Although it gives quality beef the costs are high, and demand is for good beef at an attractive price.
E.M. Hutton is Chief of the CSIRO Division of Tropical Agronomy, Mill Road, St. Lucia 4067, Queensland, Australia.
Over the last 15 to 20 years Australian research in tropical cattle production has shown that beef for domestic and overseas markets can be produced at low cost on improved tropical pastures.
The tropics have considerable potential to meet the escalating world demand for beef through extensive pasture improvement. Australia and a number of countries in South America and Africa have vast areas of tropical grasslands, savannas and forests with infertile acid soils. Some of the main areas involved are the speargrass zone of northeastern Australia, the cerrado and Amazonian regions of Brazil and the llanos of Venezuela and Colombia. These lands are unsuitable for cropping and relatively cheap, but sown to improved legume-based pastures are capable of producing quantities of good low-cost beef.
A dense Townsville stylo pasture (receiving 125 kg/ha/year molybdenized single superphosphate) under grazing at Rodd's Bay, central Queensland.
Grazing beef cattle are self-propelled and self-feeding, and with minimum inputs convert fibrous pasture into high-quality protein.
The pasture system, in contrast with the crop-and-grain fattening system, has a low demand for fossil fuels. With improved and fertilized legume-grass pastures the meat yield is increased substantially by higher stocking rates, reduced time to reach slaughter weight, higher calving percentages and earlier mating of heifers. In the dry season cattle usually maintain or gain liveweight on improved pasture, which has higher quality and greater drought tolerance than native grassland.
Tropical pasture improvement is in its infancy in many countries and its development depends on combining existing knowledge with a vigorous research programme. Research should be concentrated on the provision of adapted legumes and grasses, the correction of soil nutrient deficiencies, and the efficient utilization of pasture by grazing animals. These are the three main aspects discussed in this article.
Tropical legumes and grasses in improved pastures
Australia is singularly deficient in indigenous legumes and grasses that can be used as the basis for improved pastures, and most of our tropical pasture cultivars are derived from introductions from Central and South America and Africa. There is considerable scope for Latin American and African research workers to select promising pasture cultivars from their wealth of native legumes and grasses. The short supply of relatively cheap seed of pasture cultivars is a major factor limiting large-scale pasture improvement in many countries of the tropics.
The tropical legumes developed in Australia include Townsville stylo (Stylosanthes humilis), perennial stylo (S. guyanensis), siratro (Macroptilium atropurpureum), centro (Centrosema pubescens), greenleaf desmodium (Desmodium intortum), glycine (Glycine wightii), puero (Pueraria phaseoloides), and the tree leucaena (Leucaena leucocephala). A number of these have several cultivars, and where necessary new ones are selected or bred to overcome deficiencies.
Townsville stylo was an accidental introduction into northern Australia around 1900. When it is sown into native speargrass (Heteropogon contortus) pastures, particularly with superphosphate, year-round productivity is markedly increased (Shaw, 1961). Many Stylosanthes ecotypes have been introduced into northern Australia, and a number have been selected as potential new pasture legumes. A S. hamata line has recently been released as a new legume cultivar, named Verano Caribbean stylo, which is more productive and persistent than Townsville stylo (Anon, 1973). Selected lines of S. viscosa and S. scabra also show promise for Australia's drier monsoonal tropics. The most important tropical grasses include guinea (Panicum maximum), green panic (P. maximum var. trichoglume), buffel (Cenchrus ciliaris), Rhodes (Chloris gayana), setaria (Setaria anceps), pangola (Digitaria decumbens) and signal (Brachiaria decumbens). Some mention should be made of Paspalum plicatulum, which can tolerate very acid soils. Since a high proportion of tropical pastures is grass which rapidly loses feeding value with maturity, there is a distinct need for new grass cultivars with better ability to maintain intake and digestibility during the year. In legumes the decline of nutritive value with age is slow, so pastures with a high legume content tend to maintain quality and animal production throughout the year. Sufficient legume in the pasture also prevents crude protein levels from falling below 7 percent and limiting intake of the tropical grasses in the pasture (Milford and Minson, 1966). Wellmanaged and highly productive legume-grass pastures contain about 40 percent legume at the height of the growing season (Evans, 1970).
Some examples of tropical legume-grass mixtures for poor solodic and latosolic soils and their seeding rate per hectare are as follows:
With the exception of leucaena, there is usually no difficulty in establishing most of the legumes and grasses listed. The most expensive method of establishment is to remove and burn the trees and plough and cultivate the land to give a good seedbed for the pasture mixture. A cheaper procedure is to reduce tree density by Tordon1 killing, graze the native pasture closely or burn it, and then establish the pasture mixture on the surface with a disk cultivator, a seeder-superphosphate spreader and a roller, all linked and drawn by a tractor. A suitable application of single superphosphate is essential at establishment and once a year thereafter to maintain the balance and vigour of legume-grass pastures on poor acid soils.
Summer growth of Peru leucaena at the Samford Pasture Research Station near Brisbane.
Leucaena, a valuable tree legume
Leucaena thrives on well-drained soils in the tropics where annual rainfall is 900–1 000 mm or more. It can be used as a special purpose high-protein forage (Hutton and Bonner, 1960) for finishing steers quickly and for promoting high milk yields from dairy cows. Beef cattle grazing this legume often gain 1 kg per day. Because of its drought resistance leucaena is able to provide high-quality cattle feed in the dry season, when there is often a critical shortage of protein and digestible energy. It can contain up to 10 percent of the undesirable cell-division inhibitor, mimosine (Hegarty et al., 1964), which is usually broken down in the rumen, but can at times cause loss of rump and tail hairs, and temporary loss of condition.
Leucaena is adapted to calcareous soils, but grows well on acid soils. Establishment on the latter can be assisted by an application of 250 kg/ ha calcium carbonate in addition to 250 kg/ha or more of the essential superphosphate. Seed is treated in water at 80°C for 4 minutes, and after inoculation with the specific rhizobium is sown just below the surface at 4 kg/ha in rows 2.5–3 m apart. During establishment leucaena is very susceptible to weed competition. When it is approaching a metre in height a suitable grass, such as guinea, setaria, pangola or Brachiaria decumbens, can be planted between the rows to give a highly productive two-level pasture. Pangola and B. decumbens are high-quality grasses which are too competitive for most trailing legumes, and their association with leucaena utilizes their advantages without recourse to an expensive regime of N fertilization.
A well-balanced siratro-Nandi setaria pasture at the Samford Pasture Research Station near Brisbane.
Under favourable conditions wellestablished leucaena-grass pasture can be grazed at 2.5 or more beasts per hectare, preferably on a rotational basis with long grazing intervals to minimize mimosine problems and maintain persistence and vigour. The pliable stems of leucaena are resistant to treading and are also an important factor in its persistence. Proper attention to stocking rates will maintain a well-balanced stand, but if necessary a heavy slasher will control growth which is out of reach of the animals.
Mineral deficiencies in soil
Amelioration of plant nutrient deficiencies in the different soils is vital for the persistence and productivity of improved legume-grass pastures. Nitrogen is usually deficient in poor acid soils and can be supplied by legumes or nitrogenous fertilizers. The latter are not profitable except in very favourable situations, and there are various problems associated with their use: other major nutrients, such as P, S and K, are required; loss of nitrogen to the air; acidifying effects; the level of management needed; and the relatively low nutritive value of the bulk of grass produced (Henzell, 1968).
The failure of improved legume-grass pastures in some tropical areas is often due to the scant attention given to plant nutrition problems. The principal requirement for the maintenance of pasture productivity is usually single superphosphate supplying both P and S, which are of equal importance in legume and grass nutrition (Andrew and Robins, 1969a; Andrew et al., 1974). The nitrogen level in pasture legumes is closely related to their P content (Andrew and Robins, 1969b). The need for liming is minimal as most important tropical legumes (except glycine) and grasses are adapted to acid soils, the legumes having the ability to extract Ca from low-Ca soils (Andrew and Norris, 1961).
Centro growing at the Beerwah Research Station, 80 km north of Brisbane.
The Ca and rhizobium requirements of tropical legumes have been documented (Norris, 1966, 1967) and some, including leucaena and several Stylosanthes species, need specific rhizobium. Mo deficiency is common in legumes grown in acid soils, and is corrected with periodic applications of 100–200 g/ha of the element from molybdenum trioxide added to the superphosphate used, or by pelleting the legume seed with the trioxide (Kerridge et al., 1973), or with pasture sprays with solutions containing ammonium or sodium molybdate. The trace elements Cu and Zn are sometimes required, and deficiencies of K occur in some soils and can develop in old pastures with a long grazing history.
Supplies of relatively low-cost superphosphate are vital if Latin American, African and some southeast Asian countries are to intensify beef production by using legume-based pastures. To supply enough of the essential P and S for the pasture system, an application of 125 kg/ha/year of single superphosphate is usually needed if annual rainfall is less than 1 000 mm, and 250 kg/ha/year or more if the rainfall is above 1 000 mm. The value of the additional beef produced from a vigorous wellbalanced pasture in northern Australia is at least ten times the cost of the superphosphate required. In very acid soils (pH 4.0–5.0) soluble phosphates react with Al and Fe compounds to form insoluble products, but lime applications of 250 kg/ha or more increase the availability and utilization of the P by pasture plants. Where 250 kg/ha/year of superphosphate are used, beef production removes only 2 kg/ha/year of P from the legume-grass system, so regular superphosphate applications result in P accumulation in the soil to a depth of 10–12 cm. As superphosphate has a marked residual effect (R.K. Jones, 1968), a stage could be reached where animal production would not be markedly affected by reducing the quantity of annual maintenance dressings or by using periodic applications, particularly in drier areas. However, the P accumulation in the soil is only slowly available to pasture plants, so it needs systematic replenishment with readily available P (as in superphosphate) to maintain vigour, especially of the legumes.
Plant needs for P can be assessed by soil analysis, but as the plant integrates soil and environmental factors the best indicator of P and other nutrient requirements of pasture is foliar analysis, particularly of the legume (Andrew, 1968).
Pasture systems for increased beef production
In the tropics, unimproved native pastures will occupy the greater area of most farms for a considerable time to come, so that an integrated system which will make best use over the year of both the improved and native pastures is needed. Overgrazing of improved pasture, which could be used for finishing steers and for the mating season of cows to increase their reproductive rate, must be prevented. Native pastures produce young growth of fair quality early in the growing season, but as they mature feeding value falls rapidly. In particular, native pastures become markedly deficient in protein, so they are better utilized in the dry season with supplements such as urea-molasses drum licks (Alexander, 1972). The following are examples of various legume-based pasture systems which have greatly increased beef production in northern Australia, and which could be applied in similar areas in other tropical countries.
Droughtmaster cows (Shorthorn X Brahman) grazed continuously at 0.4 per hectare on Townsville stylo-speargrass pasture (receiving 125 kg/ha/year single superphosphate), at the Lansdown Pasture Research Station near Townsville.
The moist coastal wallum of south Queensland, with annual rainfalls from 1750 mm in the south to 1 000 mm in the north, is an area with highly infertile white acid sands where research has developed productive legume-based pastures (Bryan, 1973; Evans and Bryan, 1973). A few similar areas occur in other tropical zones. Heavy initial applications of single superphosphate, CaCO3 and KCI, with additions of the minor elements Cu, Zn and Mo, are needed for pasture establishment. The annual maintenance required per hectare is 250 kg superphosphate and 60 kg KCl. Legumes included greenleaf desmodium, Miles lotononis (Lotononis bainesii) and white clover (Trifolium repens), and the grasses included pangola, paspalum (Paspalum dilatatum), setaria and P. plicatulum. Grazed at 2.47 steers/ha these pastures gave liveweight gains of up to 365 kg/ha in the southern wallum and 480 kg/ha in the northern wallum. Kenya white clover (T. semipilosum) is a legume which could increase the productivity of wallum pastures (R.J. Jones, 1973).
The wet tropical coast of north Queensland, originally under rain forest, has affinities with extensive areas in other parts of the humid tropics. The annual rainfall is 1 800– 4 500 mm, and soils range from basaltic through metamorphic to granitic and some originate from beach sands. Suitable pasture plants include the legumes centro, puero, perennial stylo and hetero (Desmodium heterophyllum) and the grasses guinea, para (Brachiaria mutica), signal and pangola. The pasture mixture (1) described on p. 3, involving centro, puero, perennial stylo and guinea grass, receiving 250 kg/ha year superphosphate plus any deficient minor elements, will carry 3–4 steers/ha and produce annual liveweight gains up to 900 kg/ha (Teitzel et al., 1974). In this area the legume hetero has the ability to form balanced productive pastures with the grasses pangola and signal, which are usually too competitive for associate trailing legumes.
The extensive native speargrass zone of central and south Queensland is at present the most important beef-producing area in northern Australia, and is similar to large cattle areas in the tropics, such as central Brazil. At Rodd's Bay in central Queensland, with an annual rainfall of 850 mm and a dry season of four to five months, seeding Townsville stylo into speargrass with applications of 125 kg/ha/year molybdenized superphosphate increased the annual stocking rate of native pastures three times, from 0.27 to 0.82 steers/ha, and liveweight gain/ha/year six times, from 25 to 150 kg (Shaw, 1961; Shaw and 'tMannetje, 1970). Other benefits from this pasture included the marketing of steers almost two years earlier than had previously been possible and the ability to maintain cattle during droughts.
Similar results have been achieved on poor granite soil at the Narayen Research Station 320 km northwest of Brisbane, with an annual rainfall of 700 mm and a dry season of seven and a half to eight months. Native speargrass pasture fertilized with 125 kg/ha/year molybdenized superphosphate and grazed at 0.27 steers/ ha/year gave a mean liveweight gain of 34 kg/ha/year, whereas similarly fertilized siratro-Biloela buffel grass pasture grazed at 1.09 steers/ha/year gave a mean liveweight gain of 147 kg/ha/year ('tMannetje, 1973). Steers entered the pastures at 10 months of age and were slaughtered 12 months later; the siratro-buffel grass gave first-quality carcasses of 250 kg and the native pasture secondgrade carcasses of 212 kg. In the severe droughts of 1968–69 the improved legume-grass pasture carried 0.82 steers/ha/year and fattened them.
The hot dry monsoonal tropics of north Queensland and the Northern Territory, which cover a considerable area with less than 1 000 mm annual rainfall and a severe eight-month dry season, are similar to other tropical semiarid regions such as northeastern Brazil and parts of coastal Venezuela. At the Lansdown Pasture Research Station (870 mm rainfall/year) near Townsville in Queensland, pastures of Townsville stylo-speargrass grazed for four years at 0.4 and 0.8 Droughtmaster cows/ha gave mean calving rates of 66 percent with no superphosphate, 74 percent with 126 kg superphosphate/ha/year and 85 percent with 377 kg superphosphate/ha/year (Edye et al., 1971). The superphosphate increased liveweight of cows, weight and percentage of weaned calves (Edye et al., 1972) and the pasture levels of P and S. The P content of the pasture components and the S content of Townsville stylo were significantly correlated with cow conception rates (Ritson et al.,1971). At 0.4 cows/ha the pastures became dominated by perennial grasses, and at 0.8 cows/ha by Townsville stylo and annual grasses, so that this pasture system has proved to be unstable at Lansdown. It is also unstable at Katherine (890 mm rainfall/year) in the Northern Territory, and the development of more stable systems based on the perennial Stylosanthes species S. hamata, S. viscosa and S. scabra is a major research aim.
The triple combination of improved legume-based pastures, superphosphate and selected tropical cattle has resulted in spectacular and profitable increases in beef production in the Australian tropics. The adaptation and application of this pasture technology to local conditions in a number of tropical countries could result in the same growth in their beef output. Lack of the essential pasture seeds and superphosphates in sufficient quantities and at prices the farmer can afford limits any extensive improvement of tropical pastures and cattle production in a number of the countries of Latin America, Africa and southeast Asia. Commercial seed production is a specialized activity, and needs every encouragement in a country if it is to be successful. Fortunately, the world is richly endowed with phosphate resources (Phillips and Webb, 1971) and in the tropics high priority should be given to exploration for indigenous rock phosphate and the establishment of strategically placed superphosphate works. Without superphosphate it will be impossible to start realizing the potential of the vast tropical areas of infertile acid soils to produce the low-cost beef badly needed by a protein-hungry world.
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