Advances in agronomy volume 22

Role o f Plant Introduction The vital role of plant introduction in the development of pastures has been recognized for many years in the United States and Australia, both of which are

AGRONOMY

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AGRONOMY

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CONTRIBUTORS TO VOLUME 22 ix

PREFACE xi

TROPICAL PASTURES E M HUTTON 1 I I 111 IV V VI VII VII1 IX X XI XI1 XI11 XIV xv XVI I I 1 I11 IV V Introduction

Role of Plant Introduction

Tropical Legumes

Temperate Legumes d in the Subtropics

Nodulation and Nitrogen Fixation of Tropical Legumes

Undesirable Compounds in Tropical Legumes

Physiology of Tropical Legumes

Breeding and Genetics of the Main Legumes

The Main Grasse

umes

Phosphorus and Nitrogen Fertilization of Grass Breeding and Genetics of Tropical Grasses Beef Production from Legume-Based Tropi Summary and Conclusions

References

Climate and Potential for Improved Pastures in the Tropics

Legume Nutrition Relative to Tropical Pasture Development

CLAY-ORGANIC COMPLEXES A N D INTERACTIONS M M MORTLAND

Bonding Mechanisms in Clay-Organic Complexes

Nature of Some Clay-Organic Complexes and Reactions

Nature and Importance of Some Clay-Organic Complexes in Soils and Sediments

Conclusions

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113 I14

V

vi CONTENTS

BIRDSFOOT TREFOIL

ROBERT R SEANEY A N D PAUL R HENSON

I Introduction

11 Morphology

111 Physiology

IV Culture

V Utilization

V1 Genetics and Cytology

References

120 122 125 127 139 143 147 153 THE CONFIGURATION OF THE ROOT SYSTEM IN RELATION TO NUTRIENT UPTAKE K P BARLEY I Introduction I59 11 Geometrical Description of the Root System 161

111 Nutrient Transference in the Soil 167

IV Physiological Conditions Governing Uptake 17 1 V The Influence of Configuration on Uptake 177

VI Conclusions 197

References 198

FROST AND CHILLING INJURY TO GROWING PLANTS H F MAYLAND A N D J W CARY I Introduction 203

f Protein Structure 206

Ill Cold Lability of Enzymes 2 15 IV Membrane Composition and Permeability

V Protection from Freezing

VI Conclusions

THE PLATINUM MICROELECTRODE METHOD FOR SOIL

AERATION MEASUREMENT

D S M C ~ N T Y R E

I The Method

I1 Electrochemistry

111 Physical Effects of Electrode Insertion

I V Models and Microelectrode Response

V Conclusions

V1 O2 Flux and Plant Response

VI1 Summary

References

1 I 1 111 IV V VI VII VIII RATOON CROPPING D L PLUCKNETT J P EVENSON A N D W G SANFORD Introduction

Genetic Aspects

Botanical and Physiological Considerations

Ratooning and Environmental Factors

Soil Relationships

Pests and Disease

Management

Future Outlook

References

235 241 266 268 276 278 281 281 286 293 294 300 305 312 317 323 326 GRASS TETANY OF RUMINANTS D L GRUNES P R STOUT AND J R BROWNELL 1 Introduction 332

11 Incidence Climate, and Season 332

I11 Symptoms of Animals 336

Iv soils 340

V Forage 342

V l l l v1 VII VIII IX X 1 I1 I11 IV V VI VI1 CONTENTS Animal Factors in Hypomagnesemia

Treatment of Affected Animals

Prevention of Grass Tetany

Magnesium Deficiency in Humans

Summary

References

THE MICROFLORA OF GRASSLAND FRANCIS E CLARK A N D ELDOR A PAUL Introduction

The Microflora of the Living Plant

The Microflora of Grassland Litter

The Microflora of Grassland Soils

Biomass and Bioactivity Measurements

The Humic Component of Grassland Soil

Nitrogen Transformations in Grassland Soils

References

Author Index

Subject Index

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368

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375

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385

395

403

409

416

426

431

459

Numbers in parentheses indicate the pages on which the authors’ contributions begin

K P BARLEY (159), Waite Agricultural Research Institute, Glen

Osmond, South Australia

J R BROWNELL* (331), Kearney Foundation of Soil Science, Davis,

Calif0 rn ia

J W CARY (203), Snake River Conservation Research Center, Soil and Water Conservation Research Division, Agricultural Research Serv- ice, U S Department ofAgriculture, Kimberly, Idaho

FRANCIS E CLARK (373, U S Department OfAgriculture, Fort Collins, Colorado

J P EVENSON (28% University of Queensland, Brisbane, Australia

D L GRUNES (33 11, U S Plant, Soil and Nutrition Laboratory, U S

Department of Agriculture, Ithaca, New, York

PAUL R HENSON ( 1 19), U S Department of Agriculture, Beltsville, Maryland

E M HUTTON ( l ) , Commonwealth ScientiJic and Industrial Research Organization, Division of Tropical Pastures, Cunningham Labor- atory, Brisbane, Australia

D S MCINTYRE (235), Commonwealth ScientiJic and Industrial Re- sea re h organization, Canberra , Australia

H F MAYLAND (203), Snake River Conservation Research Center, Soil and Water Conservation Research Division, Agricultural Research Service, U S Department of Agriculture, Kimberly, Idaho

M M MORTLAND ( 7 3 , Michigan State University, East Lansing, Michigan

ELDOR A PAUL (373, The University of Saskatchewan, Saskatoon, Canada

D L PLUCKNETT (285), College of Tropical Agriculture, University of Hawaii, Honolulu, Hawaii

W G SANFORD (285), College of Tropical Agriculture, University of Hawaii, Honolulu, Hawaii

ROBERT R SEANEY ( 1 19), Cornell University, Ithaca, New York

P R STOUT (331), Kearney Foundation of Soil Science, Davis, Cali- fornia

*Present address: Fresno State College, Fresno, California

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In keeping with one of the basic objectives ofAdvances in Agronomy,

this volume covers a variety of subjects of concern to crop and soil scientists Likewise, the sixteen North American and Australian authors who contributed these papers have a breadth of backgrounds and interests They have covered topics vital to both public and scientific concerns The continuing world-wide attention to tropical agriculture is recog- nized in this volume An analysis is made in one chapter of the potential, and the problems, of ratoon cropping -a practice of considerable im- portance with tropical crops such as bananas, sugar cane, and pine- apples An extensive review of research to improve and utilize tropical pastures relates to the potential for forage production in the tropics The problems involved in the production and utilization of a number of im- portant tropical forage species are also emphasized While one is impressed with the research contributions, the opportunities and problems ahead present challenges which dwarf these accomplishments of the past Two other chapters relate to the animal industry as well as crop pro-

duction One is a review of the research on birdsfoot trefoil (Lorus corni-

cularus L.), an important pasture and forage legume of especial value

in the North Central and Northeastern states The second deals with grass tetany, a ruminant animal malady associated with forages low in magnesium and often relatively high in nitrogen and potassium Factors affecting the animal disorders, probable reasons for them, and thera- peutic techniques are reviewed

A review of recent research findings on frost and chilling damage to plants includes evidence as to the mechanism of damage, and informa- tion on methods of preventing or reducing this damage In another chapter the relationship of geometric configuration of roots to nutrient uptake is examined Research is reviewed which identifies the conditions under which nutrient transfer in the soil and root system configuration

1 im it nutrient up take

Growing public concern for environmental quality has forced a real- istic consideration of the part tne soil might play as a sink for various kinds of wastes Included are pesticides and other exotic chemicals, sewage, and similar wastes One chapter is addressed to a review of the reaction of soils (clays) with organic compounds The increasing spec- ificity of our knowledge is impressive but the need for greater under- standing of these reactions in soil is even more obvious

The soil environment for plant roots and other living organisms is considered in two chapters A critical review of the platinum electrode

xi

PREFACE xii

method for measuring soil aeration casts some doubt on the interpretation

of earlier findings, especially those wherein so-called critical values of oxygen flux for root and plant growth were established The microflora

of grasslands and grassland soils is discussed in one chapter These con- tributions will be especially helpful as background for those concerned with ecosystems and how man is modifying them

AGRONOMY VOLUME 22

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E M Hutton

Commonwealth Scientific a n d Industrial Research Organization

Division of Tropical Pastures Cunningham laboratory

Erisbane Australia

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IV

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IX

X

Introduction

Climate and Potential for Improved Pastures in the Tropics

Role of Plant Introduction

Tropical Legumes

ecies

C The Desmodiums

D Glycine ( G wightti)

F Miles Lotononis ( L bainesii)

G Dolichos and Vigna Species

H Centro (Cenfrosema pubescens)

1 Calopo (Calopogonium mucunoides) and Puero (Pueraria Temperate Legumes Used in the Subtropics

A Hunter River Lucerne

B Barrel Medic

C White Clover

Nodulation and Nitrogen Fixation of Tropical Legumes

Legume Nutrition Relative to Tropical Pasture Development

Undesirable Compounds in Tropical Legumes

A B Mimosine

C Indospicine

E Leucaena ( L leucocephala)

Estrogens and Substances Causing Bloat and Milk Taints

pica1 Legumes

A B Townsville Stylo

C Glycine wightii

D Siratro

E African Trifoliums

Breeding and Genetics of the Main Legumes

A Breeding Systems

B Townsville Stylo

C Siratro

D Desmodiums

1

Temperature and Growth in Several Tropical Legum

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2 E M HUTTON

, f ~

F Leucaena

G Indigofera

H Lucerne

XI The Main Grasses

A Brachiaria

B Cenchrus

C Chloris

D Cynodon

E Digitaria

F Melinis

G Panicum

H Paspalums

I Pennisetum

J Setaria

K Sorghum

L Urochloa

XII Feeding Value of Grasses versus Legumes

A Phosphorus

B Nitrogen

XIV Breeding and Genetics of Tropical Grasses A Setaria

C Coastal Bermudagrass

A Wet Tropics C Humid Subtropics

D Subhumid Subtropics

XVI Summary and Conclusions ,

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1 Introduction

Improvement of tropical grasslands was neglected for many years be- cause most of the areas involved are in developing countries with pressing sociological and economic problems Also, it had been concluded (Whyte

et al., 1953) that it would be very difficult to introduce a legume into

tropical grasslands and establish legume-based pastures as productive as those in temperate areas It was left to grassland scientists in several countries, including Hawaii (Takahashi, 1956), Jamaica (Motta, 19561, the Congo (Germain and Scaut, 1960), and Australia (J G Davies, 1960),

to pioneer research on legume-based pastures for the tropics This work was intensified and expanded mainly at experiment stations in north-

eastern Australia and Hawaii At some of the centers significant progress has been made in solving the problems of tropical legume-grass pastures The staff of the C.S.I.R.O Cunningham Laboratory in Brisbane sum-

marized their findings (C.A.B Bull 47, 1964) for the benefit of pasture workers in other tropical areas More recently, in 1966, W Davies and

Skidmore edited a book, “Tropical Pastures,” which presents the modern approach to tropical pastures

Now that reliable tropical legumes and grasses are available as well

as knowledge of their fertilization, management, and productivity, con- siderable interest has been stimulated in the tropics in the use of improved tropical pastures for animal production A rapid expansion in the areas planted with tropical pasture species can be envisaged with a concomitant increase in production of beef and milk so that the “protein drought” in many countries will gradually disappear The development of pasture eco- systems for the wide range of environments throughout the tropics will present many new problems This will require increasing research activity

in many countries on pasture and animal production and a swing away from the preoccupation with veterinary and animal health problems

II Climate and Potential for Improved Pastures in the Tropics

The tropics and its agricultural development are discussed by Phillips

(196 1) and Webster and Wilson ( 1 966) Wet equatorial climates with con-

stant heat, rainfall, and humidity occur mainly within 5” to 1O”N and S of

the equator over a large area of South America and in West Africa, Malay- sia, Indonesia, the Philippines, New Guinea, and various Pacific Islands Annual rainfall is usually 80- 120 inches, but a higher maximum is ob-

tained in a number of places The crops grown include rubber, oil palm, banana, coffee, coconut, cocoa, and rice, and experiments and some commercial plantings have shown that productive pastures can be es- tablished in the wet tropics

Between the low latitude zones of wet equatorial climate and the Trop-

ics of Cancer and Capricorn (23 M”N and S) there are extensive areas with annual rainfalls of 20-80 inches and with a tropical monsoon climate in

which there is an alternation of wet and dry seasons These areas occur

in South America, West and Central Africa, India, and in countries of Southeast Asia including Burma, Thailand, Laos, Cambodia, and Viet- nam, and also in northern Australia Four climatic zones can be distin-

guished in these monsoonal areas as follows: annual rainfall of 40-80

inches in two rainy seasons with short dry seasons; annual rainfall of 25-50 inches in two short rainy seasons with pronounced dry seasons;

4 E M HUTTON

annual rainfall of 30-50 inches in one fairly long rainy season with a long

dry season; and annual rainfall of 20-40 inches with one short rainy

season and a long dry season Rainfall reliability decreases at the lower rainfalls In the wetter parts, perennial tropical crops are grown as in the wet tropics Where dry seasons are well defined, annual crops like rice, cotton, and maize are important, and in the driest areas sorghum, bulrush millet, and peanuts are grown The tropical monsoonal areas have con- siderable potential for improved pastures and cattle production, as shown

by some of the results obtained in different regions (vide Norman and

Arndt, 1959; Shaw, 196 1 ; Stobbs, 1969a)

The moist tropical climate extends from the Tropics of Cancer and Capricorn to about latitudes 35"N and S, respectively, to give zones with

a humid subtropical climate (McIntyre, 1966; C L White et al., 1968)

These encompass southeastern United States, the middle Orient, a zone including southern Brazil, southern Paraguay, northern Argentina, and Uruguay, and areas along the eastern coasts of South Africa and Australia These humid subtropical transition zones have a rather variable rainfall

(Griffiths, 1959), which is predominantly in summer but with a winter increment Usually referred to simply as the subtropics, they are impor- tant agriculturally and grow the hardier tropical crops and, as shown in

Australia (J G Davies and Eyles, 1965), have considerable potential for

the development of cattle pastures based on tropical legumes and grasses

The subtropics of eastern Australia is described by Coaldrake (1 964) as

the region where plants may be subjected to water stress or surplus any month of the year and where water, rather than energy, is more likely to limit plant production Coaldrake also commented on the drastic reduc- tion of herbage quality caused by a relatively small number of rather mild winter frosts in these areas Their sudden onset allows no hardening of plants, and in any case most tropical pasture plants originated in frost- free areas and their above-ground portions, though usually not the roots, are killed by frost Most of the recent cultivars that are having an impact

on tropical pasture development in Australia and elsewhere were selected

and developed at research centers in Australia's subtropics (J G Davies and Eyles, 1968) Thus, in Australia, the subtropics and Tropics form a

continuum in which the factors governing pasture production vary in degree rather than in principle

As outlined, the tropical zones where there is distinct potential for increased cattle production on improved pastures include the wet equa- torial, the tropical monsoonal, and the humid subtropical covering ap- proximately 27% of the world's area Of the moist tropics, 33% is wet

tropics, 49% monsoonal, and 18% subtropics The arid tropical zone,

with its deserts, the dry subtropical with xerophytic scrub, herbs, and grasses, and the semiarid tropical of grassland steppes are zones where the vegetation can be improved with range management techniques and not usually with the use of sown species As pointed out by Hutton (1968a), 60% of the world’s cattle are in the moist tropics, where 10%

is cropped, 20% is pasture, 35% is forest, and a third is wasteland Forest areas and wasteland are often in hilly areas and attempts to crop them result in soil erosion With the use of the new tropical pasture species and fertilizer, idle uplands and unimproved native pastures can be improved markedly with significant effects on beef and milk production

Ill Role o f Plant Introduction

The vital role of plant introduction in the development of pastures has been recognized for many years in the United States and Australia, both of which are deficient in promising native pasture species in their temperate and also tropical areas Although the tropics of Latin America and Africa are rich in indigenous legumes and grasses with potential value for improved pastures, Kenya is the only country in these continents where a study has been made of the important species of native grass- lands (Edwards and Bogdan, 195 I)

The U.S.D.A plant introduction services, which commenced in 1898 (vide Yearbook of Agriculture, 1962) and which are now vested in the New Crops Research Branch, have not been particularly concerned with

introducing tropical pasture plants However, pangolagrass (Digitaria

decumbens), which was introduced as vegetative material from South

Africa in 1935 by the then U.S.D.A Division of Plant Exploration and Introduction, has made a major impact on tropical pasture improvement (Oakes, 1960) Interest in Digitaria was stimulated and led to the col- lection by Oakes (1965) of an extensive range of species and ecotypes within the genus The breeding of coastal bermudagrass (Burton, 1954), which has significantly increased pasture production in the southeastern United States, was achieved through the use of two tall-growing South

African introductions of Cynodon dactylon U.S.D.A plant introduction work has also assembled species in the genus Paspalum, such as P nota-

turn, and P dilatatum and obtained species for the Hawaiian Experiment Station in the legume genus Desmodium

As a result of the work on indigenous grasses in Kenya (Edwards and Bogdan, 1951) the tropical world has obtained valuable ecotypes of a

number of grasses including Rhodes (Chloris gayana), buffel (Cenchrus

ciliaris), star (Cynodon dactylon), molasses (Melinis minutiflora), guinea

The Kenyan example could well be emulated in the countries of Central and South America, where there is a wealth of indigenous legumes wait- ing to be collected, classified, and assessed Latin America is the source of

a few important grasses, notably in the genus Paspalum, but does not possess as valuable a grass flora as Africa Although Africa has an ex- tensive range of native legumes, it has not as yet contributed as many promising pasture legumes as Latin America There is an awakening interest in many tropical countries in introduction of tropical legumes and grasses that have shown promise elsewhere Most of them still show a reluctance to investigate their own rich native flora for promising pasture plants

As pointed out by Hutton (1970), Australia is singularly deficient in indigenous legumes and grasses that can be used as the basis for improved pastures and increased animal production As a result, there has been a continuing interest in Australia in pasture plant introduction, which com- menced on a random basis about the 1880’s and became organized in

1930 with the establishment of the Plant Introduction Section of the

C.S.I.R Division of Plant Industry (McTaggart, 1942) Up to the present, 50,000 introductlons have been brought into Australia and 6 I % of these are pasture and forage species Much of the current pasture development

in the Australian Tropics is based on the chance annual introduction

Townsville stylo (Stylosanthes humilis) which was recognized at Towns-

ville around 1900 and known formerly as Townsville lucerne Intro- duction of tropical pasture species has been a major aim of C.S.I.R.O

plant introduction work since its inception, and a large number of legume and grass accessions from tropical countries have been evaluated over the years The selection of grasses adapted to northern Australia has been relatively easy, whereas obtaining adapted legumes has proved difficult, particularly for the subtropics, where rainfall is variable and frosts can occur

Since the turn of the century, the Australian wet tropics of about 4 million acres of northeastern coastal country between Mossman and Mac- kay has had adapted introductions of tropical grasses such as guinea,

molasses, and para (Brachiaria mutica) Schofield ( 1941) eventually

obtained successful legumes for this area including stylo (Stylosanthes

guyanensis), centro (Centrosema pubescens), puero (Pueraria phaseo- loides), and calopo (Calopogonium mucunoides)

Much of the plant introduction work for northern Australia over the last thirty years has aimed at obtaining legumes and grasses for pasture development in the extensive tropical monsoonal and humid subtropical areas between latitudes 30"s and 11"s and comprising about 260 million

acres (J G Davies and Eyles, 1965) Miles ( 1 949) made distinct progress

with this problem by evaluating an extensive range of introduced legumes and grasses in central coastal Queensland from 1936 to 1946 He showed that the low mineral and protein status of the native pastures could be raised by perennial legumes in a number of genera including Arachis, Centrosema, Desmodium, Glycine, Indigofera, and Stylosanthes The

most promising grass introductions included ecotypes of Chloris gayana,

Cenchrus ciliaris, Digitaria sp., Panicum maximum, Paspalum notatum, Setaria sphacelata, and Urochloa sp Miles' results (1 949) stimulated

the first work in overseas plant exploration by Australia Hartley (1949)

joined a U.S.D.A expedition to subtropical South America and collected mainly ecotypes of species in the genera Arachis, Desmodium, Stylo- santhes, and Paspalum From these introductions the cultivars Oxley

Fine-stem stylo and Hartley plicatulum (Paspalum plicatulum) (Bryan

and Shaw, 1964) have been selected

Another ten important overseas collections of pasture plants have been made by Australians in tropical monsoonal and humid subtropical

areas during the period 1952-1968 (Hutton, 1970) A range of material was collected, particularly in the legume genera Centrosema, Desmodium, Glycine, Phaseolus, and Stylosanthes, and the grass genera Cenchrus, Panicum, Paspalum, Setaria, and Urochloa Only the introductions from

J F Miles' visits to South Africa and east and west Africa in 1952 have been fully evaluated These have yielded Miles Lotononis (L bainesii)

(Bryan, 1961), Rongai Dolichos lablab (W,ilson and Murtagh, 1962), and

Samford Rhodes grass R J Jones' collections ( 1 964) of Setaria spha-

celata from East Africa have already produced the frost-tolerant culti-

var Narok setaria, and it is anticipated that further promising lines will

come from these The systematic exploration in 1965 of legumes and a

few of the grasses by Williams ( 1966) in the main states of Brazil, and in

Bolivia, Paraguay, and northern Argentina, has substantiated that these areas are rich in indigenous species potentially valuable as tropical and subtropical pasture plants Williams found annual types of stylo similar to Townsville stylo in a number of regions

8 E M HUTTON

Due to the progress made on plant exploration and introduction for the tropics, it is now more difficult to find native legumes and grasses which are superior to existing pasture cultivars This is no reason to cur- tail this activity, as only a fraction of the almost unlimited variation in the indigenous flora of countries like South and Central America and Africa has been investigated With the advances in knowledge of the feeding value of pastures relative to species and management, variants of present cultivars or even new species could be required and may well be found among the native plants of these and other countries In any case, the pasture plant breeder needs a continual flow of new genetic material which can be obtained only through plant exploration and introduction

IV Tropical Legumes

Australian research centered in Queensland is now in the forefront

on the introduction, selection, and development of legumes for tropical pastures This has resulted from the realization that legume-based pasture

is the most economical method for the development of the cattle industry

in the vast unused coastal and subcoastal areas of northern Australia (J G Davies and Eyles, 1965) Maintenance of around 40% of a phos- phate-responsive legume in a tropical pasture is the cheapest way to provide nitrogen for the pasture and grazing animal (Hutton, 1968b)

In this section the origin and agronomic features of the principal tropi- cal legumes commercialized in Australia will be discussed For their detailed descriptions, see Barnard (1 967) Some, like the drought-re-

sistant Townsville stylo and siratro (Phaseolus utropurpureus), are

adapted to a wide range of conditions in northern Australia, whereas those including centro, glycine, the desmodiums, and Miles lotononis, are less drought tolerant and more restricted in their adaptation With the exception of Miles lotononis, aboveground growth of all the tropicals is killed by frost, which is a constant feature of the subtropics in winter However, the perennial crown and root systems survive and regenerate unless subjected to intense and repeated frosting As larger areas of the different tropical legumes are established, they will become hosts to various diseases and pests which could affect persistence of some culti- vars Fortunately the main legumes do not appear to be affected by root- knot nematodes, and siratro is highly field resistant (Hutton and Beall,

1957) The root-damaging Amnemus weevil (Amnemus quadrituber-

culutus) is a serious pest of glycine and the desmodiums on the north coast of New South Wales, whereas Miles lotononis and lucerne are re-

sistant and siratro is seldom attacked severely (Braithwaite, 1967; Mears, 1967) Other native weevils have damaged a number of the legumes in

north Queensland The bean fly (Melanagromyza phaseoli) can seriously damage Murray lathyroides (Phaseolus lathyroides) throughout the

season but siratro, affected only in the seedling stage, can be protected

by seed treatment with dieldrin (R J Jones, 1965) The viruslike disease

“legume little leaf” due to a mycoplasma (Bowyer et al., 1969) affects a

number of the legumes and under relatively dry conditions markedly re- duces stands of the desmodiums and Miles lotononis, and causes some loss in siratro In high rainfall areas, varying amounts of defoliation is

caused by Rhizoctonia solani in several legumes, particularly siratro

Commercial seed production of the different legume cultivars is in-

creasing in Australia and several other countries In Kenya Desmodium

intortum, silverleaf desmodium ( D uncinatum), Glycine wightii, Sty-

losanthes guyanensis, Dolichos lablab, and Trifolium semipilosum are

sold whereas in South Africa and Brazil G wightii is the one usually

harvested for sale

A STYLOS

1 Townsville Stylo (S humilis)

The history and potential of the annual Townsville stylo is sum- marized by Humphreys ( 1967), who noted that its natural spread is con- fined to the north of Western Australia, the Northern Territory, and Queensland It has thin, fibrous stems and narrow elongated and pointed leaves, and forms a dense stand under favorable conditions Flowers are yellow and inconspicuous and arranged in a short compressed spike The brown pods are hooked, have two segments, but usually contain only one true seed The hooked pods cluster into small balls and comprise the

commercial seed, the yields of which range from 400 to 700 Ib per acre

As a result of D F Cameron’s work (1965) with naturalized ecotypes,

three vigorous upright cultivars, Gordon (late), Lawson (midseason), and Paterson (early black seeded) are being commercialized

Townsville stylo (Fig 1) is grown widely in Australia, particularly from latitudes 1 1 “ S to 24”s and where the annual rainfall is between 25 and 7 0

inches It flourishes on poor sandy soils but does not establish readily on deep cracking clays and in waterlogged areas Seed is sown at 3-4 lb per acre in conjunction with 1 cwt superphosphate per acre by aerial or ground methods into grazed open woodlands or cleared and cultivated areas It is susceptible to shading from vigorous associate grasses, so it

10 E M HUTTON

FIG I Townsville stylo, Narayen Research Station, near Mundubbera, Queensland

should be kept well grazed Where there is strong grass competition, as in the Northern Territory, Stocker and Sturtz ( 1 966) and H P Miller ( 1967) obtained satisfactory establishment of Townsville stylo by sowing it immediately after a burn early in the wet season which rapidly destroyed growing native grasses A fall of rain of an inch or more in early summer will cause rapid germination of seed The young seedlings are quite drought resistant, but a prolonged dry period will cause their death The high actual seed yields of 800-1000 Ib of seed per acre and the high per- centage of hard seed ensure the persistence of Townsville stylo

Norman and Arndt ( 1959) in the Northern Territory and Shaw ( 196 1 )

in central Queensland proved the value of Townsville stylo in beef pro- duction and so paved the way for its widespread use in northern Australia

It is proving successful in the tropical monsoonal areas of Southeast Asia, the Philippines, Brazil, Central America, and East Africa as well

as in southern Florida (Kretschmer, 1965)

2 S c h o j e l d Stylo (Stylosanthes guyanensis)

This perennial, which originates from Brazil (Schofield, 1941), is naturalized in the wet Tropics of northeastern Australia It is tall and

branched with hairy stems, narrow pointed leaflets, and compact spikes of small yellow flowers Seeding is profuse, and the small brown single- seeded pods shed o n ripening, which makes mechanical harvesting difficult

Schofield stylo grows in frost-free conditions in northern Australia

where annual rainfalls are 35-160 inches, summer temperatures are high,

and soils remain moist It is sown at 2 Ib per acre, usually after cultiva-

tion, grows well on both poor and fertile soils, and is compatible with tropical grasses like guinea and molasses Heavy grazing and fire will soon reduce stands of this legume

A few recent introductions of S guyanensis from central and South America are superior to Schofield stylo, as they are prostrate and branch vigorously from the base under heavy grazing Various ecotypes of perennial stylo are being increasingly grown in east Africa and will no doubt be grown more widely in the Tropics

3 Oxley Fine-Stem Stylo

This stylo came from Paraguay and was one of Hartley's collections (1949) It was selected as a result of Shaw's work (1967a,b) on granitic spear grass soils of southern Queensland It is semiprostrate, well

12 E M HUTTON

branched, and has an underground crown The leaflets are narrow and pointed, and the small yellow flowers are in compact spikes The brown single-seeded pods fall very rapidly as they ripen, which makes harvest- ing particularly difficult

Oxley fine-stem stylo is frost and drought tolerant and is adapted to the ligher soils of Australia’s subtropics in annual rainfalls of 28-50 inches

It is sown at 1-2 Ib per acre and is compatible with buffel and Rhodes

grasses

B PHASEOLUS SPECIES

I Siratro ( P atropurpureus)

Siratro (Fig 2) is a perennial bred from two Mexican ecotypes of P

atropurpureus (Hutton, 1962) I t has deeply penetrating swollen roots and a high level of drought resistance If the soil is moist for an extended

FIG 2 Siratro growing at Sarnford Pasture Research Station, near Brisbane, Queensland

period, the trailing pubescent stems root at random along their length Its twining habit allows it to reach the light in dense pastures Leaves have three ovate leaflets with dense silvery hairs on the lower surface The evidence indicates that siratro is a short-day plant with abundant flower- ing and seeding occurring when vegetative growth is checked by dry weather or cooler conditions in autumn The relatively large flowers are

in a raceme and are deep red, and age to dark purple before withering The pods are narrow and cylindrical and they shatter as they ripen from the raceme base Actual seed yields are around 800 Ib per acre under favor- able conditions but commercial yields are 100- 150 Ib per acre because of shattering Seed is usually scarified to reduce the percentage of hard seed Siratro grows from latitude 1 1 "S to 30"s in Australia in annual rainfalls

from 25 to 70 inches and thrives on a variety of soils, particularly those

well drained Seed is sown at 2-3 Ib per acre on well grazed native grass- land or cultivated areas, and establishment is rapid under favorable conditions It is compatible with a range of grasses including Rhodes,

buffel, green panic (Panicum maximum var trichoglume), guinea, and

Nandi setaria and its growth is rapid at the height of the wet season Siratro, due to its perenniality, high actual seed yield, and quick re- generation from seed, is usually quite persistent provided year round stocking rates are kept within reasonable limits of a cattle beast to

1.3-3.0 acres

Siratro is promising in tropical monsoonal areas in the countries of Central and South America and eastern Africa In eastern Africa its growth is restricted at elevations above sea level of 4500 feet or more Good growth of siratro is also reported from New Guinea, Fiji, Phil-

ippines, Rajasthan (Patil et al., 1967), southern Florida (Kretschmer,

1966), and Southeast Asia

2 Murray lathyroides ( P lathyroides)

Murray lathyroides was first reported in the Brisbane district toward the end of the last century (Bailey and Tennison-Woods, 1879) and is now naturalized along the coast of northeastern Australia Ecotypes of

P futhyroides are widely distributed and grow wild in a number of coun-

tries of Southeast Asia, Central and South America, and Africa and also

in New Guinea, the Pacific and Hawaiian Islands, southern Florida, West Indies, Philippines, and India They vary from upright to prostrate and have either sparse or strong basal branching Murray lathyroides is an

erect vigorous annual or biennial with some branching and smooth

14 E M H U T T O N

lanceolate leaflets The conspicuous deep pink to red flowers are in a raceme, and the narrow cylindrical pods shatter as they ripen from the raceme base

Murray lathyroides was developed by Paltridge ( 1942) because of its vigor, palatability, and high protein content It grows well in pasture mixtures, on a range of soils in annual rainfalls of greater than 30 inches and is seeded into cultivated land at 2-3 Ib per acre Periodic cultivation

is necessary to ensure its regeneration from fallen seed An important attribute is its ability to persist on heavy-textured waterlogged soils

The role of the desmodiums as pasture plants has been summarized by Bryan (1966, 1969) Greenleaf (D intorturn) and silverleaf ( D uncina- turn) are the two commercialized in Australia A number of D canurn

and D sandwicense ecotypes have been introduced, but none have shown real promise as yet, although kaimi Spanish clover (D canurn) has proved of value in Hawaii (Hosaka, 1945; Younge et al., 1964) D gyruides, a shrub used to prepare land for cocoa in Fiji and elsewhere, has potential for forage as it persists under grazing and produces green leaf in the dry season in frost-free areas The strongly stoloniferous D

heterophyllurn, naturalized in a number of tropical countries, has per- formed well in association with aggressive grasses like pangola in the wet Tropics of north Queensland

1 Greenleaf (D intorturn)

Indigenous ecotypes of D intorturn are common in Central America and Brazil (Williams, 1966), and greenleaf is a mixture of three similar introductions from El Salvador and Guatemala It is rather a coarse trail- ing perennial which roots along the pubescent stems under moist con- ditions and has a fibrous root system (Fig 3) The deep green, rounded leaflets often have a reddish brown to purple flecking on the upper sur- face Short days induce flowering and the small deep lilac to pink flowers are in compact terminal and axillary racemes The small narrow and re- curved seed pods are segmented and have hooked hairs that cause them

to adhere to clothing and animals Seed yields of 100-120 Ib per acre are being obtained under irrigation in the dry season

Greenleaf thrives on a variety of soils in the coastal areas of northern Australia where annual rainfall is 40 inches or more and the dry season not too severe, as in the Northern Territory It is not particularly drought resistant and grows well in moist elevated areas as the Atherton Table-

FIG 3 Greenleaf desmodium, Samford Pasture Research Station, near Brisbane, Queensland

land of north Queensland It is sown at 2 Ib per acre in pasture mixtures into cultivated land, and establishment is often slow because of retarded

16 E M HUTTON

nodulation Once established, it grows rapidly under warm moist con- ditions and is compatible with most of the tropical grasses Leaves and shoots are quite palatable to cattle (Bryan, 1966), and it thins out at stocking rates in excess of a beast to the acre

Types of D intorturn similar to greenleaf have performed well in trials

in Tanzania and Uganda (Naveh and Anderson, 1967; Stobbs, 1969a) and a number of other tropical countries Near the equator it grows from sea level to elevations of 6500 feet, so is very adaptable

2 Silverleaf ( D uncinatum)

Silverleaf desmodium was introduced from Brazil in 1944, and more recently Williams (1966) collected similar ecotypes from there It is a trailing perennial with thin, ovate, hairy leaflets which have a broad irregular silver band along the midrib Moistness induces rooting along the pubescent stems, and swollen as well as fibrous roots are produced Flowering occurs in short days, and the paired lilac to mauve flowers are borne in open terminal and axillary racemes The segmented sickle- shaped pods have hooked hairs, and the seeds are flat and larger than those of greenleaf Commercial seed yields of 200-300 Ib per acre are

obtained

Silverleaf is not as hardy as greenleaf and thrives only in moist coastal areas of northeastern Australia where annual rainfall is 40 inches or more Growth is restricted by high summer temperatures so elevated areas with

cooler nights often provide it with a better environment It grows on a variety of soils and is sown in mixtures at 2 lb per acre on cultivated

land Establishment is usually rapid and it combines well with grasses like the setarias, panicums, and paspalums Palatability of leaves and shoots is high (Bryan, 1966), and it is susceptible to overgrazing

Silverleaf desmodium has proved promising in several countries, notably in East Africa (Bogdan, 1965; Naveh and Anderson, 1967) More recent results have indicated that it will be replaced there by green- leaf or a similar type of D intorturn It is of interest that at Palmerston

North, New Zealand, silverleaf was the only tropical legume surviving in the third season from a range which was sown

D GLYCINE ( G wightii)

The perennial G wightii is mainly indigenous to Africa, although there

are some Southeast Asian forms Descriptions are given by Verboom

( 1965) of the five main types in Zambia and by Bogdan ( 1966a) of the five distinct African types he assembled in his plots at Kitale in Kenya

Bogden ( 1 966a) found that G wightii occurred to an altitude of 7000 feet

in Kenya and that the three outstanding varieties agronomically in his collection were Kenyan in origin Glycine is a promising legume in a

number of other countries including Brazil (Neme, 1958) and Tanzania (Naveh and Anderson, 1967)

The three Australian cultivars of glycine have been selected from a series of African introductions Clarence came from the South African

Transvaal (Murtagh and Wilson, 1962), Cooper from Tanzania (Edye and Kiers, 1966), and Tinaroo from Kenya (Kyneur, 1960) They are trailing

and twining, and root along stems in contact with the soil; Tinaroo and Cooper are more stoloniferous than Clarence All have a strong taproot, and Tinaroo and Cooper have finer stems and are more branching than Clarence They have ovate leaflets; those of Tinaroo are thin, smooth, and bright green, those of Cooper are softly hairy and ash green, and those of Clarence are coarse and hairy with brown pigmentation Cooper and Clarence are early flowering, but Tinaroo is very late The racemes are many flowered, and the flowers are small and white with violet streaks

on the standards, which are pink tinged except in Tinaroo The pods are straight and flattened, and commercial seed yields of 200-300 lb per acre are obtained

Glycine thrives only in northeastern Australia on kraznozems and black self-mulching clay soils where annual rainfall is 30-70 inches It

is not adapted to the long, hot dry seasons of the far north of Australia nor to the large areas of solodic and podzolic soils along the coast Glycine

is sown in mixtures at 2-4 lb per acre in cultivated soil Although slow to establish in the first year, it combines well with a range of grasses if care- fully managed during this period

E LEUCAENA ( L leucocephala)

Both Oakes (1968) and Gray ( 1 968) have reviewed the relevant facts

concerning the origin, agronomy, and use of the promising high-protein forage tree, leucaena It is indigenous to Central America and has spread

to the Caribbean islands, the Philippines, and Southeast Asia, to the Hawaiian and other Pacific islands including Fiji and New Guinea, and to the northern Australian coast from Darwin around to Brisbane No doubt its use as a shade tree for cocoa and coffee accelerated its spread Interest in its use as a forage for cattle was first engendered by Takahashi and Ripperton ( 1 949), who obtained yields from it of 8-9 tons of dry

matter per acre containing 1-1.5 tons of protein in a 50-60 inch rainfall

in Hawaii Since then it has been used for cattle fattening in the Hawaiian

Hutton and Gray (1959) grouped leucaena introductions into three types These are the short, bushy, early Hawaiian type, the tall, late, sparsely branched El Salvador type, and the tall, late, strongly branched Peru type The low-yielding Hawaiian type is the one naturalized in northeastern Australia and around Darwin El Salvador and Peru are the cultivars commercialized in Australia, but Peru is preferred because

it has the highest dry matter and protein yields (Hutton and Bonner, 1960) and the best growth habit for grazing (Fig 4) Leucaena is a deep-rooted tree with a high level of drought resistance It has smooth bipinnate leaves with narrow leaflets, small white flowers in a globose head, brown strap-

FIG 4 A productive stand of Peru leucaena, Samford Research Station, near Brisbdne, Queensland

shaped pods, and very hard glossy brown seeds At present commercial seed is harvested by hand, and 300 Ib per acre is easily obtained Leucaena grows successfully in northern Australia on a range of well drained soils where the annual rainfall is 30 inches or more and frosts are light or absent It is one of the few tropical legumes adapted to highly calcareous soils (Oakes and Skov, 1967), and indications are that it is

responsive to lime as well as to phosphate Satisfactory establishment

requires that seed be planted at 3-4 Ib per acre in rows 8-10 feet apart

into well prepared soil and that weeds be controlled by interrow cultiva- tion or herbicides Seed needs to be treated by immersion for 4 minutes

in water at 80°C to ensure a good germination When the young trees are

growing vigorously they are no longer susceptible to competition, and an associate grass like guinea, green panic, setaria, or pangola can then be planted between the rows The resultant two-level pasture can be heavily stocked, as the pliable stems of leucaena are not damaged by grazing If leucaena grows out of reach of the animal it can be controlled by a heavy mechanical slasher Leucaena gives high liveweight gains and no deleteri- ous effects in cattle if grazed in rotation with non-leucaena pastures (see

Section VIII, A, p 33)

F MILES LOTONONIS (L bainesii)

This perennial cultivar came from seed collected in the Worcester Veldt Reserve of South Africa by J F Miles in 1952 The agronomic features of Miles lotononis are described by Bryan (1961), who com-

mented on the need to introduce further L bainesii ecotypes and increase variability available for improvement in its adaptability L bainesii is

indigenous over several million acres of the northern Transvaal and

Rhodesia, and a number of variants have been collected (Smith, 1969)

As yet, Miles lotononis has shown adaptation to only limited areas in various tropical countries

Miles lotononis is slender, prostrate, and stoloniferous and roots at the nodes only in sandy and self-mulching soils It has strong taproots and

a degree of drought resistance Leaves are digitate trifoliate with smooth, narrow, and pointed leaflets The small yellow flowers are in a raceme or open head and the small brown pods release the minute seeds from a basal

opening Commercial seed yields are 50-60 Ib per acre

Miles lotononis is adapted to friable soils, particularly sandy types,

in humid subtropical areas where annual rainfall is 35-40 inches or more

It is the only frost-resistant summer legume, but grows slowly at low temperatures The seed requires inoculation (Norris, 1958) and is sown

20 E M HUTTON

at 0.5-1.0 lb per acre on cultivated soil Initially the seedlings are slow growing and sparse, but later they grow into a dense cover under warm moist conditions It forms balanced mixtures with a number of grasses including pangola provided constant grazing pressure is maintained Miles lotononis does not persist on tight soils At times it almost disap- pears from sandy soils but usually recolonizes these

G DOLICHOS A N D VIGNA SPECIES The genera Dolichos and Vigna are closely related and contain a high proportion of quick growing annual and biennial types In dolichos there are three cultivars, Rongai lablab (D lablab), Archer axillaris (D axil-

h i s ) , and Leichhardt dolichos (D uniforus) Dalrymple vigna (V lute-

ola) is the only vigna cultivar at present

Rongai lablab (Wilson and Murtagh, 1962) was collected in Kenya by

J F Miles It is a tall vigorous and well branched biennial with broad ovate leaflets and relatively large white flowers, and becomes rampant

and trailing under favorable conditions Seed yields of 500-600 lb per

acre are obtained It thrives on a variety of soils where the rainfall is 25

inches or more and is replacing cowpeas (Vigna sinensis) in many areas

The relatively large seed is sown at 10-15 lb per acre Rongai lablab is drought and cold tolerant and is used as a forage crop and as a preparation for sowing perennial pastures At maturity the stems are woody and un- palatable to animals

Archer axillaris from Kenya is a trailing and twining short-term peren- nial with glossy leaves and small greenish yellow flowers Commercial

seed yields are 200-500 Ib per acre It is sown at 2-4 Ib per acre in well drained frost-free areas where annual rainfall is 40 inches or more and is

valued for its rapid growth in both spring and summer (Luck, 1965) Leichhardt dolichos is a short-season twining annual with softly tomen- tose leaves and small greenish yellow flowers Sown at about 10 lb per

acre, it grows on a variety of soils where annual rainfall is 25-45 inches

and produces heavy seed yields of 1000 Ib/acre or more held in the pod for dry season grazing (Staples, 1967)

Dalrymple vigna, a biennial, was collected in Costa Rica by W W Bryan It is trailing with shiny, bright green leaflets and roots along stems

in contact with the soil The flowers are large and yellow, and commercial seed yields of around 150 Ib per acre are obtained Sown at 5-10 Ib per

acre, it grows on most soils where annual rainfall is 35-40 inches or more and will grow under waterlogged or saline conditions It is very palatable, and at Samford Pasture Research Station persisted only two years under grazing (R J Jones et al., 1967)

H CENTRO (Centrosema pubescens)

Centro is indigenous to South America and is an important perennial

in wet tropical pastures around the world It has a strong taproot and is trailing and twining with some nodal rooting Leaflets are bright green and

shiny, and it has large mauve flowers Seed yields of 300-500 Ib per acre

are obtained It is seeded at 4 Ib per acre and thrives in combination with grasses like para and guinea on most soils in the wet tropics where annual rainfall is 50 inches or more On the north Queensland coast, centro- based pastures have persisted and maintained high animal productivity

with proper management and fertilization A W Moore (1962) in Nigeria and Bruce (1965) in Australia have shown that centro significantly in-

creases soil fertility

I CALOPO (Calopogonium mucunoides) A N D

PUERO (Pueraria phaseoloides)

Calopo is native in Central and South America and is naturalized throughout the wet tropics It is a trailing short-term perennial with oval leaflets invested with brown hairs The flowers are small and pale blue,

and seed yields are 200-300 lb per acre Sown at 2-3 lb per acre, it is a

good pioneer on most soils and produces a thick stand not very palatable

to cattle It is not favored for general use

Puero, or tropical kudzu, is native to Malaysia and is a perennial It is trailing and twining, with broad, dark green leaves and long, vigorous runners The flowers are of medium size and white with a violet blotch

Seed yields are 300-400 Ib per acre It is a pioneer legume in the wet Tropics and is sown at 2-3 Ib per acre Puero is very palatable and disap-

pears under heavy grazing

V Temperate Legumes Used in the Subtropics

In Australia’s subtropics with its increment of winter rain, the winter-

and spring-growing lucerne (Medicago sativa), barrel medic ( M trunca-

tula), and white clover (Trifolium repens) are of increasing importance

in pastures as complementary species to tropicals Their frost resistance ensures that their quality .is not reduced by the light frosts that often occur

in winter Inclusion of temperates in subtropical pastures could be tried elsewhere, as it maximizes the period during the year when pasture of good feeding value is available

A HUNTER RIVER LUCERNE

Hunter River, an old lucerne cultivar (Whittet, 1923), is the main type

grown, and Christian and Shaw ( 1 952) first showed its importance in the

22 E M HUTTON

subtropics 't Mannetje ( 1967) found that inoculation and lime-pelleting seed of Hunter River enabled it to grow in combination with tropical species in the extensive areas of acid granitic soils of the speargrass zone south of the Tropic Hunter River lucerne is already important on the fertile brigalow soils and can be grown as far west as the 18-inch isohyet

in southern Queensland It is an erect perennial with wedge-shaped leaf- lets and violet flowers and has a deep taproot and the crown at the sur- face Hunter River does not persist well in the subtropics because of intolerance to continuous grazing and rotting of old crowns in the moist summer It may eventually be replaced by more productive cultivars like Siro Peruvian or African (D G Cameron, 1968) or with a lucerne bred specifically for subtropical pastures (Bray, 1967)

B BARREL MEDIC The cultivars Cyprus and Jemalong have proved valuable on both the solodics and clay loams of the brigalow zone of southern Queensland (J S Russell, 1970) They are semiprostrate annuals with hairy leaflets, and each Jemalong leaflet has a prominent purple-brown blotch whereas the leaflets of only a few plants of Cyprus have this blotch A number of runners are produced, and the flowers are small and yellow; Cyprus is about a month earlier than Jemalong Profuse production of the barrel- shaped pods occurs, and seed yields of 300-500 lb per acre are obtained These cultivars usually persist after introduction into an area because of

a high percentage of hard seed Regeneration from seed is good under favorable conditions

C WHITE CLOVER

A number of cultivars of white clover, including Grasslands Huia, Irrigation, and Ladino, have been successful in subtropical pastures along the moist coast from northern New South Wales to Maryborough in southern Queensland (Andrew and Bryan, 1955) They are also used in lower latitudes on moist tableland areas such as the Atherton Tableland

of north Queensland White clover is a valuable pasture component be- cause of its high digestibility and feeding value lt is mainly annual in habit in northeastern Australia, but abundant seed production ensures its persistence

Kenya white clover (Trifolium semipilosum), which has a strong peren-

nial root system and greater drought tolerance than white clover ('t Man- netje, 1964), could replace white clover in some areas when its establish- ment problems are overcome

VI Nodulation and Nitrogen Fixation of Tropical Legumes

Rapid and effective nodulation of legumes is essential for their estab- lishment and vigorous growth and for significant amounts of nitrogen and protein to be added to the pasture ecosystem Henzell (1962) found that nitrogen fixation of several tropical legumes was substantial although not quite at the level of white clover and lucerne By inclusion of centro in giant star grass (Cynodon dactylon), A W Moore ( 1 962) obtained an in- crease of 250 lb of nitrogen per acre foot per annum under the pasture and raised nitrogen content of the grass from 1.8 to 2.4% R J Jones et al

(1967) showed that the increase in total nitrogen yield of pasture from inclusion of tropical legumes was directly related to legume yield It is estimated (Henzell, 1968) that nitrogen fixation by tropical legumes in northern Australia is 20-260 Ib an acre a year depending on level of leg- ume yield At Beerwah, near Brisbane, silverleaf desmodium increased soil nitrogen by 30-77 Ib an acre a year relative to amount of applied

superphosphate (Henzell et al., 1966) Addition of relatively high levels

of superphosphate to Townsville stylo in the field raised the nitrogen yield

to 3.3 times and the dry matter yield to 2.4 times those at nil superphos- phate (Shaw et al., 1966) Supporting glasshouse and controlled environ- ment experiments showed that sulfur produced the major increase in ni- trogen fixation, and phosphorus the major increase in dry weight

Field nodulation of some tropical legumes was studied by Whiteman and Lulham ( 1970) and Whiteman ( 1 970a,b) In undefoliated plots, both silverleaf desmodium and siratro had marked summer (February-April) peaks in nodule and plant dry weight Cutting and grazing reduced nodule number per plant in silverleaf desmodium and mean weight per nodule in siratro In greenleaf, desmodium and siratro effects of defoliation were not evident for 18 days, but then reduction in nodule weight per plant was re- lated to severity of the initial defoliation Seasonal buildup and decline of the nodule population in three desmodiums were not related to onset of flowering Peak nodulation occurred 3 months before flowering in green- leaf and 1 month before in silverleaf

Most of the tropical legumes will grow and nodulate freely on acid soils: this is partly because they have the ability to extract calcium from these low-calcium soils (Andrew and Norris, 1961) This is of con- siderable significance in the economic development of pastures in the extensive areas of solodic and podzolic soils low in calcium in the moist tropics and subtropics of northern Australia Costly lime applications are unnecessary for vigorous legume growth, and only superphosphate with

or without molybdenum is usually needed for high production of legume-

24 E M HUTTON

based pastures Norris ( 1956) concludes that the valuable attributes of tropical legumes are a reflex of their origin and that of their associated slow-growing cowpea type of Rhizobium under tropical rainforest con- ditions of low fertility He regards tropical legumes and the cowpea Rhizobium as the progenitors of temperate legumes and their more specialized rhizobia A study by Norris ( 1965) of the acid production of a large number of Rhizobium strains resulted in their separation into slow growing alkali-producers mainly from tropical legumes and fast growing acid-producers mainly from temperate legumes These findings help to explain the adaptation of tropical legumes to acidic soils of low nutrient status and of temperate legumes to fertile alkaline soils Another interest- ing finding by Norris ( 1959) was that Rhizobium is not calcium-sensitive and requires trace amounts of calcium only, but has a much greater need for magnesium This has resulted in the use of dolomite in the mixtures used for pelleting clover seed (Hastings and Drake, 1962)

Present knowledge concerning the inoculum and lime requirements of tropical legumes as summarized by Norris ( 1966, 1967) is given in Table I Among the legumes having cowpea Rhizobium, there is a range from unspecialization to strain specificity and this represents different stages

of development The promiscuous legumes as shown in Table I include siratro, Townsville stylo, and cowpea, and these nodulate freely and grow without inoculation and lime additions However, if they are inoculated with a selected strain of Rhizobium, a marked increase in growth and nitrogen fixation often occurs (Norris, 1966) The more specialized types like centro, the desmodiums, glycine, and Miles lotononis require inocu- lation with selected rhizobia but no lime Silverleaf desmodium has inferior ability to extract calcium from poor soils compared with Stylo- santhes species (Andrew and Norris, 196 l ) , and the same has been found for glycine, but lime is only occasionally beneficial, and the selected rhizobia they require are still cowpea types Miles lotononis is an in- teresting example of a legume which grows successfully in sandy soils

as acid as pH 4.0 and which requires a highly specific red Rhizobium

originally obtained from South Africa (Norris, 1958) Finally Table I

lists the highly specialized types, including leucaena, lucerne, and ordinary and Kenya white clovers which need acid-producing and fast- growing rhizobia and respond to lime Norris (1959) and Norris and 't Mannetje (1964) showed that central African Trifolium species like Kenya white clover are highly specific and will not nodulate with common clover rhizobia Leucaena is exceptional among the tropicals in this respect, which explains its adaptation to calcareous soils and soils of high

TABLE I

A Guide to lnoculum and Lime Requirement of Legumes Used in Tropical Pastures

Expected lime lnoculum

Calapogonium mucunoides Calopo

Siratro Golden gram Murray lathyroides Mung bean Tropical kudzu Schofield stylo Oxley fine-stem Townsville stylo White clover Kenya white clover Dalrymple vigna Cowpea stylo

N o

N o

N o Rarely, in extreme

N o

N o

N o Occasionally at

pH below 5.5 Yes

N o Yes, lime is conditions

N o

N o

Cowpea" Specific Desmodium Desmodium Cowpea" Cowpea" cowpea Cowpea Specific Specific Lucerne

Cowpea" Cowpeắ Cowpea" Cowpea" Cowpeá' Cowpea" Specific Cowpea" Clover Specific Cowpea" Cowpea"

The question of lime-pelleting tropical legume seed for preservation of the applied rhizobia and their successful establishment on the roots

during germination and early growth is discussed by Norris ( 1 966, 1967)