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SUMMARYPastures of Digitaria decumbens (pangola grass) previously oversown with Lotononis bainesii at Mount Cotton, south-east Queensland, Australia, were grazed by sheep for 3 years (1985–87), using a factorial combination of seasonal variations in stocking rate.Lotononis behaved as a short-lived plant with a mean half-life of 4·2 months (range 1·6–10·3); rate of mortality was positively related to initial seedling density. The proportion of lotononis remained very low for the first 2 years of the experiment, when conditions were unsuitable for large-scale seedling regeneration, which was also limited by the hardness of the seed reserves. Subsequently, lotononis regenerated well in treatments which combined the following features: (i) light grazing (5 sheep/ha) during the main flowering period of spring-early summer, (ii) heavy short-duration grazing in mid-summer to create a ‘gap’ and (iii) medium or heavy (18 or 27 sheep/ha) grazing during late summer-autumn to reduce competition from pangola grass.The ecological niche of lotononis and the possible use of complementary pastures are discussed.

Grasslands around the world are a resource of great economic importance, as the origin of most of the world's milk and wool and much of the meat. The growing world population and global warming have put increased pressure on the world's grasslands. Ross Humphreys has played a leading role in the development of grassland science and in this authoritative review discusses how it has evolved over the past sixty years. Using the proceedings of the International Grassland Congress since 1937, Professor Humphreys identifies the shifting emphasis of the science, assesses the current state of play and looks at perspectives for the future. This review will be of great value to all grassland scientists and ecologists.

Recent research suggests that the application of the old concepts of pasture management developed in Europe, USA and South Africa have been unsuccessful in the Tropics; in some areas under-utilisation has resulted in poor animal output and low economic returns, whereas in other areas overgrazing has resulted in soil erosion and weeds. This book sets out to examine the problems involved in the utilisation of tropical and subtropical pastures and to explain how pastures may be managed to meet the requirements of both plants and animals for growth and replacement. Following an overview of the livestock systems of the tropics, the effects of grazing animals on the edaphic, biotic and climatic environment of the pasture are described. The response of the animals to the available pasture are discussed in terms of pasture attributes of nutritive value and sward structure, selectivity and grazing behaviour. Methods for attaining continuity of forage supply are also described. The author, Professor L. R. Humphreys, has been involved for many years in extensive research of tropical and subtropical pastures. A central objective of his work has been to effect a synchrony between pasture available and the forage requirements of the animal. This book is a culmination of much of his research and will be invaluable to all disciplines with an interest in tropical and subtropical agricultural practices.

Lotononis bainesii seeds were sown in a glasshouse at 0, 10, 20 or 30 mm depth, covered with 0, 70, 140, or 210 g m litter and grown under shades giving 24, 47, 77 and 100% light transmission. Light negatively influenced the extension of the hypocotyl above ground level and positively increased the contractile growth of the hypocotyl to produce a buried crown. Emergence from 10 and 20 mm depth and the absence of litter also favoured development of a buried crown. In the field the extension of the hypocotyl of seedlings was negatively related to the light received by the seedlings, as varied by companion Digitaria decumbens growth. A buried crown did not develop in the absence of grazing. Maintenance of grazing pressure following seedling regeneration favours increased L. bainesii density in mixed pastures. -from Authors

Macroptilium atropurpureum cv. Siratro was grown in large soil beds with a constant water table below, developing a dawn leaf water potential of --0.25 MPa. Water stresses equivalent to -0.7 or -1.0 MPa were developed over 14 d, causing reduced stem and bud elongation, leaf expansion, and bud differentiation and survival. Apex size, the proportion of buds which were floral or vegetative, the early phases of floral initiation, and seed formation on advanced inflorescences were little affected during the water deficit period.Upon rewatering previously stressed plants showed increases relative to control plants in the rates of shoot appearance, leaf expansion and new node appearance. The ratio of buds becoming floral was independent of watering treatment, and the enhanced rate of floral bud production in the previously-stressed treatments was due to higher rates of total bud differentiation which persisted for up to six weeks after rewatering. Survival of floral buds was reduced by previous stress, but number of flowers per inflorescence, pod setting, seed number per pod and 100-seed weight were independent of treatment. Seed production was controlled by inflorescence density. Rate of seed production was independent of treatment during water deficit and four weeks subsequently, and was then enhanced by 46 and 54 per cent relative to the control in the -0.7 and -1.0 MPa treatments respectively.

SummaryAmmonium nitrate was applied to a kikuyu (Pennisetum clandestinum) dominant pasture at annual rates of 0, 134, 336 and 672 kg N/ha. Each nitrogen (N) rate treatment was continuously grazed at three stocking rates (SR) designed to apply similar grazing pressures at each N level and covering a range from 2·2 to 16·6 Angus weaner cattle/ha.The N status of these pastures was periodically assessed 8–10 weeks after seasonal N applications by temporarily excluding stock and measuring D.M. and N response to additional ammonium nitrate application. Pasture growth response to additional N was constant and independent of SR and of annual N rate over the range 0 to 336 kg N/ha, despite wide variation in pasture availability. N concentration of plant shoots was increased by high SR and rate of N uptake was not significantly affected by SR. Pasture growth rate was positively related to annual N rate.Herbage yield of kikuyu leaf, stem and litter on offer, was negatively related to SR but weight of underground organs was unaffected. Increasing SR increased the proportion of leaf and the rate of tillering. Pasture availability was positively and linearly related to N rate from 0 to 336 kg N/ha and maximal at 336 kg N/ha; the size of the litter fractions and underground organs was generally independent of N rate. N% in leaf and stem was reduced at low SR; N% of leaf, stem, litter, rhizome and root was positively related to N rate which was more influential than SR. The effect of SR on the size and relative distribution of the N in plant tops and litter fraction is discussed.Kikuyu dominance was positively related to N rate and independent of SR. White clover invaded at No and N131 levels especially at a high SR.

SUMMARYA pasture of Lotononis bainesii and Digitaria decumbens cv. Pangola at Mt Cotton, south-east Queensland was mown on six occasions at intervals of ca. 3 months and after each mowing was subjected in 1 day to the treading intensity expected from sheep grazing at 0, 7, 14, 21 and 28/ha. A movable corridor and folds were employed to walk the sheep the required number of times on eight replicates of each treatment.Lotononis regrowth was negatively related to sheep treading intensity, whereas Pangola was highly resistant to treading and grew vigorously from underground buds on rhizomes and from persisting stolons. Young lotononis seedlings were more vulnerable than older seedlings which had branched; plants developed from autonomous nodal roots were more resistant than seedlings. Attention is drawn to the contractile growth of the hypocotyl following epigeal germination which leads to a buried crown.Lotononis plants were short-lived, and seedling regeneration of ca. 27 and 47 plants/m2 occurred in the late summer of the 2nd and 3rd year after sowing. Soil seed reserves averaged 16900/m2. Studies might be undertaken of management systems directed to favouring lotononis plant replacement through accretion to seed reserves, seedling regeneration through the creation of ‘gaps’, and seedling survival through judicious timing of grazing.

Five selections of Stylosanthes guianensis var. guianensis with a short-day flowering response were grown at three sites at altitudes of 10, 280 and 1000 m on the island of Bali, Indonesia at latitude ca. 8 30’ S. Mean site temperature was ca. 6 C lower at the highest site whilst mean short-wave radiation was lowest at the intermediate site.Date of 50 % floral initiation (FI) varied from 1 February to 21 June, when daylength (sunrise to sunset plus half civil twilight) deereased from 12.85 to 12.00 h. FI was independent of site for cv. Graham and cv. Cook, but at 1000 m it was 14 and 77 days earlier for cv. Endeavour and cv. Schofield respectively relative to the 280 m site. Little flowering of cv. Schofield occurred at 10 m, and it is suggested that cool temperatures promoted an increase in the critical photoperiod for this cultivar, or that warm temperatures inhibited flowering. FI was delayed at 1000 m in CPI 34906.The duration of the phase from FI to flower appearance (FA) varied from 29 to 75 days according to selection and to site, and was negatively related to mean temperature, radiation, and maximum temperature for cv. Graham, cv. Cook, and CPI 34906 (but not for cv. Endeavour). Number of nodes at FA in this determinate species generally reflected growing conditions in the pre-flowering phase and was positively associated with age at FA in plants of particular varieties. Present address: School of Agriculture, Hawkesbury Agricultural College, Richmond, 2753, NSW, Australia.We are indebted to Universitas Udayana, Bali, Dinas Peternakan (Propinsi Bali), Penelitian Proyek Peternakan di Bali (P3B) and to the Australian Universities International Development Program for support and for facilities, to Dr I. B. Oka, Professor I. M. Nitis, Ir I. K. Rika, Drh I. B. Arka, Ir P. Sastrawan and Ir M. Oka for cooperation and assistance, and to Mrs K. Basford, Mr I. F. Horton andMr J. Benders for help with data treatment.

Swards of Brachiaria decumbens were burnt and the development of tillers emerging 5 (T5) or 10 (T10) days later was studied. The stages of raceme initiation, spikelet initiation, spikelet differentiation and inflorescence exsertion occurred in 50% of tillers c. 14.5, 21, 26.5 and 59 days after tiller emergence respectively. Growth of T5 tillers was faster than that of T10 tillers, and raceme initiation occurred when T5 tillers were slightly longer and heavier than T10 tillers, making the external identification of early development events unreliable. Attention is directed to the large variability in the development of tillers emerging on the same day and to the need for better synchrony of raceme initiation as a basis for increased uniformity of inflorescence exsertion. Copyright

SUMMARYUpland rice and Stylosanthes guyanensis were sown simultaneously in pure and mixed culture at varying densities at Na Pheng, central Laos. Vegetative growth of the rice was negatively related to stylo density over the range o to 81 stylo plants/m.2 Rice grain yield varied from 98·4 gm./m.2 in monoculture to 63·4 gm./m.2 when grown with 81 stylo plants/m.2 Rice was more competitive than stylo, but stylo growth was relatively independent of rice density over the range 20 to 120 rice plants/m.2

Seedlings of Stylosanthes guianensis var. guianensis were grown in long (14 h) days in five temperature regimes for varying periods before transfer to short (11 h) days at 30 °C/21 °C. The juvenile phase before seedlings responded to inductive conditions was c. 45-50 d, 50-60 d and 60-70 d for cv. Schofield, cv. Cook and C.P.I. 34906 respectively, which is positively related to their critical photoperiod for flowering. Temperatures favourable for growth (e.g. 30 °C/26 °C) reduced the juvenile phase in C.P.I. 34906 and in Cook, which did not flower in 11 h days unless previously exposed to more than 18 long days.In a second experiment cv. Cook was confirmed as a long-short day plant. Seedlings were grown for 50 d in a glasshouse with natural daylength extended to 13, 14, 16 or 24 h before transfer to 12 h photoperiods. Cook floral development was positively related to daylength provenance before transfer and plants in continuous 12 h did not flower.Shortening daylength after 48 cycles of 12 h to 11.75 h did not result in continued floral development in Cook plants but cv. Graham plants were initiated or transitional by 75 d.

A central issue in the husbandry of seed crops of perennial tropical grasses is the disposal of residues from previous crops. Flowering of these grasses is usually poorly synchronized, and the sudden removal of all shoot material by burning, mechanical removal or stock concentration is necessary to create a population of tillers of similar age (Humphreys & Riveros, 1986). There has been little critical study of alternative systems of residue disposal and their effects on the ways in which seed yield is realized. Questions requiring attention are whether cutting differs from burning in its effects, and whether the fuel load, determined by the size of the previous crop, influences the potentially damaging effect of fire on crown buds. This paper describes an experiment contrasting the effects on the formation of seed yield in Brachiaria decumbens of a cut and remove system of residue disposal with cut, field dry, and burn systems with varying fuel loads.

Seed production of five selections of Stylosanthes guianensis var. guianensis was studied in Bali, Indonesia (latitude 8 30’ S) with a series of harvests at three sites of increasing altitude and rainfall: (1) Sesetan, 10 m, (2) Kuwum, 280 m and (3) Pekarangan, 1000 m. Seed yield of cv. Graham, CPI 34906, cv. Cook and ov. Endeavour was maximal at Sesetan with yields of 109, 39, 38 and 166 g/m2 respectively, whilst cv. Schofield, which flowered little at low altitude, produced 12 g/m2 at Pekarangan. Optimum time of harvest varied from 26 April for cv. Graham at Sesetan to 1 November for cv. Schofield at Pekarangan. Yield stability over sites was greatest in cv. Graham, in which increased number of florets per spike at high altitude partially compensated for negative altitudinal effects on spike density. Disease reduced yields of cv. Cook and cv. Endeavour at Kuwum and Pekarangan and the incidence of rainfall at advanced stages of crop development reduced spike density and seed maturation.It is suggested that the high seed yields attained at the low altitude, low latitude Sesetan site were attained via (1) vigorous vegetative growth and a longer duration of floral induction resulting in high bud site density, (2) high bud site fertility, (3) high seed set (ca. 70-80 %), (4) high seed weight and (5) little or no disease or insect damage. The greater synchrony of flowering at higher latitude sites may be less critical for high levels of seed production than the greater length of crop development available at low latitudes.Present address: School of Agriculture, Hawkesbury Agricultural College, Richmond, 2753, NSW, Austrlia.We are indebted to Universitas Udayana, Bali, Dinas Peternakan (Propinsi Bali), Penelitian Proyek Peternakan di Bali (P3B) and to the Australian Universities International Development Program for support and for facilities, to Dr I. B. Oka, Professor I. M. Nitis, Ir I. K. Rika, Drh I. B. Arka, Ir P. Sastrawan and Ir M. Oka for Cooperation and assistance.

Seedlings of Stylosanthes guianensis var. guianensis cv. Cook and of two selections of S. guianensis var. pauciflora (CIAT 1280 and CIAT 1062) were grown at day/night temperatures of 20°/25°, 30°/25°, and 35°/30°C in a naturally‐lit glasshouse at latitude 27°30'S. Sowings were made in decreasing daylength at 30‐day intervals from 22 January to 21 May. Cv. Cook and the CIAT 1280 selection did not flower fully if sown after 22 January and the CIAT 1062 selection did not flower if sown after 22 March. This is interpreted as a long‐short day flowering response. Usually, flowers were initiated earlier and at a lower node at 25†/20°C than at the warmer temperatures. At 25†/20°C the first flowers to appear were produced predominantly at the terminal apex of the main stem in cv. Cook and the CIAT 1062 selection, but not in the CIAT 1280 selection. At the two warmer temperatures first flowers were more commonly produced at the terminal apex of primary, secondary and tertiary branches. There were more inflorescences per plant on earlier than later sown plants when measured 21 days from appearance of the first flower and the most inflorescences were produced by cv. Cook at 25†/20°C, by selection CIAT 1062 at 30°/25°C, and by CIAT 1280 at 35°/30°C. Copyright

Seedlings of Stylosanthes guianensis var. guianensis were grown for 75 days in 16 h photoperiods and transferred to controlled environment cabinets for a further 112 cycles set at 12 h days and 18, 21, 24 or 27 OC constant temperatures. Floral initiation (FI) occurred in cv. Cook after 21 short-day cycles of 12 h and was independent of temperature. Warm temperatures delayed FI in cv. Schofield and hastened it in cv. Endeavour. Rate of node appearance was positively and the duration of the phase FI to flower appearance negatively related to temperature. Spike production and floret number per spike were maximal for Cook and Endeavour at 24°C; seed setting was independent of temperature above 18°C in Cook. Growth, flowering, and seed production of Endeavour required warm temperatures, but Cook was more versatile in its adaptation to varying temperature regimens.

The potential for the increased use of pasture legumes in the tropics has excited the imagination of many scientists. Substantial resources have been directed in the past three decades to finding adapted plants and to understanding how these may be incorporated in farm practice [1]. The expectations of these programmes are directed to increased animal production and sometimes to the stabilization of cropping systems.

SummaryIndividual live-weight gain (LWG) of Angus weaner cattle continuously grazing (Pennisetum clandestinum) pasture was negatively and linearly related to stocking rate (SR) and independent of ammonium nitrate (N) application rate at similar grazing pressures.Live-weight gain varied from 380 to 1056 kg/ha according to N rate in 1970–1 and from 637 to 1477 kg/ha in 1971–2. Calculated SR giving maximum LWG/ha was 3·4, 4·7, 7·6 and 9·8 animals/ha for the 0, 134, 336 and 672kg N/ha treatments respectively in 1970–1 and 6·1, 5·7, 9·1 and 10·6 animals/ha for the same treatments in 1971–2. Highest response to applied N (1·9 and 3·4 kg LWG/kg additional N in successive years) occurred between N131 and N336; response was greater at low and intermediate SR than at high SR. Carcass weight, quality score, depth of subcutaneous fat and area of eye muscle were negatively related to SR; SR's giving maximum output per unit area caused a reduction of ca.25% in production per head and adversely affected carcass quality at 18 months of age.LWG/head was independent of feed availability in spring and summer and was positively related to availability of green kikuyu up to 600 kg D.M./head in the autumn/winter period.

SUMMARYSimultaneous undersowing of upland rice with Stylosanthes guyanensis at Khon Kaen, north-east Thailand did not affect vegetative growth of rice but reduced grain yield by 19 per cent. Grain yield was not significantly affected if stylo undersowing was delayed by 10 days. Stylo growth was reduced by one half by delayed sowing and was negatively related to dry matter yield of rice variety.

SUMMARYThe growth and nitrogen yield of Stylosanthes guyanensis undersown with upland rice were negatively related to level of urea application at Khon Kaen, north-east Thailand. In the absence of applied urea the nitrogen yield of rice monoculture was 3·3 gm./m.2 whilst the addition of stylo increased nitrogen yield of the association to 9·6 gm./m.2 Stylo was initially dominated by rice but exploited environmental growth factors more effectively in the latter part of the growing season, accentuating competition for water and phosphorus. Simultaneous stylo and rice sowing reduced rice grain yield by 12 per cent, the greatest reduction occurring at a low level of urea application, mainly due to abortion of spikelets after panicle exsertion.

Seedlings of Stylosanthes guianensis var. guianensis cv. Cook and S. guianensis var. pauciflora cv. Bandeirante were defoliated and placed in a naturally lit glasshouse at 23/18 °C, 28/23 °C or 33/28 °C (day/night). After exposure to 14 h days and after floral induction with 30 cycles of 11 h, plants were allocated to 11, 12, 13 or 14 h during flowering and seed formation.Floral initiation occurred after 10-15 short-day cycles. Flower appearance was hastened by warm temperatures and spike number per plant at 20 d after flower appearance was negatively related to temperature and greater in Cook than in Bandeirante. Exposure to 13- and 14-h days reduced the continued differentiation of inflorescences in Bandeirante, and in Cook in warm temperatures. Floret number per spike was greatest at 23/18 °C and a higher proportion of florets aborted in Bandeirante at 33/ 28 °C. Variations in seed setting of the bi-articulate loment of Bandeirante are described. Highest potential seed yield occurred if after floral induction 11 or 12 h days were maintained with 23/18 °C or 28/23 °C temperatures.

SUMMARYSheep were grazed for 2 years at stocking rates of 7, 14, 21 and 28/ha on a pasture comprising Lotononis bainesii and Digitaria decumbens cv. Pangola at Mt Cotton, south–east Queensland. There were six replicates of each treatment grazed in rotation with 3 days' grazing followed by 15 days' rest.The initial dominance of lotononis was lost after 6 months of grazing and lotononis failed to persist satisfactorily at any stocking rate. Demographic studies showed that lotononis behaved as a short-lived plant, predominantly annual, with some vegetative perennation as stolon-rooted units under heavy grazing. Soil seed reserves varied from 5800 to 400 m2 at the lightest and heaviest stocking rates respectively. Lotononis failed to regenerate under Pangola shading or inopportune high grazing pressure. Soil bulk density (0–7 cm) increased from 1·2 to 1·4 g/cm3 according to stocking rate.

SUMMARYStylosanthes humilis was grown at Brisbane at densities of 10, 50, 250, 850 and 3800 plants/m2 in boxes of sand which received basal nutrients, applications of 0, 10 and 50 kg P/ha as calcium dihydrogen phosphate, and frequent irrigation.Maximum seed yield was 69 g/m2 at a density of 850 plants/m2. Seed yield was linearly related to the logarithm of density up to 250 plants/m2, and was comparatively stable over the upper density range, declining slightly at supra-optimal density. Inflorescence density exerted the primary control over seed yield, but seed set per floret and floret number per inflorescence were also influential.The application of 50 kg P/ha increased yield of plant tops by 54% and seed yield by 20%.

SummaryPaspalum plicatulum was grown at Brisbane in boxes of sand receiving basal nutrients and frequent irrigation; weekly levels of ammonium nitrate application were varied according to growth and development stage.The rate of tiller appearance increased to a maximum 40–50 days after sowing and almost ceased thereafter. Tiller leaf number, survival, fertility, inflorescence branching, seeds per raceme and seed size were positively related to tiller age. Young tillers were more sensitive to variations in nitrogen supply than old tillers.Adequate nitrogen nutrition during the vegetative phase from sowing to floral initiation (93 days) increased tiller and hence inflorescence density; increased inflorescence branching was compensated by fewer seeds per raceme. Good nitrogen nutrition during the phase from floral initiation to inflorescence exsertion (142 days) increased survival of late-formed tillers and hence inflorescence density; inflorescence branching, seeds per raceme and seed size were also increased. Nitrogen stress during the final maturation phase did not affect seed yield.

Plant diversity is the norm in tropical pasture swards. The agronomist attempts to manipulate botanical composition in order to achieve certain ends: a desired balance of grass and legume, the suppression of inedible species, dominance of erosion-preventive plants, or a combination of species of differing seasonal growth rhythm which promotes continuity of forage availability. An understanding of the factors controlling plant interrelations is necessary to establish secure bases for management recommendations.

Plants are ecologically successful either because they survive the stresses of an environment better than other plants or because they gain a greater share of environmental growth factors, reducing the availability of these factors to other plants. This distinction is not an absolute one, but provides a convenient sequence of topics for discussion. The next three chapters outline the comparative resistance of plants to environmental stresses associated with climate, soil type and physiography, and biotic factors.

Adaptation to grazing requires resistance to defoliation, excretion of dung and urine, and trampling. ‘Defoliation’ is used to denote shoot removal. In the most extreme case it may extend to the physical uprooting of plants, but usually animals prehend, tear or cut, and ingest only part of a plant on any grazing occasion. The frequency of plant removal and the intensity of each defoliation determine the degree of pasture use. Both the amount of plant material removed and the characteristics of the residual sward after defoliation influence the pasture response, which is also conditioned by the developmental stage of the plants and the weather conditions when grazed and in the post-grazing period.

Ecologists have been quick to note the affinity between the spatial distribution of a particular species and the topographical situation and soil type on which it occurs. It is much more difficult to understand the reasons why a particular spatial distribution is found, since most of the evidence is only associative, and many soil parameters are highly correlated with one another and with other features of the physical and biotic environment. I find it difficult to accept that soil morphology per se has any pronounced influence on the adaptation of tropical pasture cultivars. Edaphic effects on plant distribution usually reflect influences on moisture availability, root temperature, oxygen activity, mineral availability and mineral excess. Current pasture research reflects two differing approaches. Pasture plants are selected which are best suited to a particular combination of these conditions, perhaps with minimal soil modification. Alternatively, ‘unsuitable’ soils and their environment can be changed to create a tolerable medium for the growth of any pasture plant. An unexplained exception to this brave generalisation is the failure of seedling regeneration of Stylosanthes humilis on cracking-clay soils.

Increased pasture yield is the traditional goal of the scientist. Certainly he has found grounds for optimism in the C4 tropical grasses. Pennisetum purpureum yielded 86 t dry matter ha−1 y−1 over 3 years in the warm humid conditions of Puerto Rico, when cut at intervals of 9 weeks and liberally supplied with nitrogen fertiliser (Vicente-Chandler et al., 1959), and there are many reports of yields in the 30–50 t ha−1 y−1 range. It is unusual to find records of temperature C3 pasture swards yielding even 23 t ha−1 y−1 under irrigated subtropical conditions (Cameron, 1964).