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VI. Nodulation and Nitrogen Fixation of Tropical Legumes

VI. Nodulation and Nitrogen Fixation of Tropical Legumes

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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 conditions 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 interesting 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 inoculation with selected rhizobia but no lime. Silverleaf desmodium has

inferior ability to extract calcium from poor soils compared with Stylosanthes 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 interesting 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 fastgrowing 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



25



TROPICAL PASTURES



TABLE I

A Guide to lnoculum and Lime Requirement of

Legumes Used in Tropical Pastures



Species



Common name



Calapogonium mucunoides

Centrosema pubescens

Desmodium intortum

Desmodium uncinaturn



Calopo

Centro

Greenleaf desmodium

Silverleaf desmodium



Dolichos axillaris

Dolichos biforus

Dolichos lablab

Glycine wightii



Archer dolichos

Leichardt dolichos

Rongai dolichos

Cooper, Clarence, or

Tinaroo glycine

Peru leucaena

Miles lotononis

Lucerne



Leucaena leucocephala

Lotononis bainesii

Medicago sutiva



Phaseolus atropurpureus

Phaseolus aureus

Phaseolus lathyroides

Phaseolus mungo

Pueraria phaseoloides

Stylosanthes guyanensis

Stylosanthes guyunensis

Stylosanthes humilis

Trifolium repens

Trifolium semipilosum

Vigna luteola

Vigna sinensis



Siratro

Golden gram

Murray lathyroides

Mung bean

Tropical kudzu

Schofield stylo

Oxley fine-stem

stylo

Townsville stylo

White clover

Kenya white clover

Dalrymple vigna

Cowpea



Expected lime

response



lnoculum

requirement



No

No

No

Rarely, in extreme

conditions

No

No

No

Occasionally at

pH below 5.5

Yes

No

Yes, lime is

obligatory if pH

is 5.5 or lower

No

No

No

No

No

No

No



Cowpea"

Specific

Desmodium

Desmodium



Cowpea"

Cowpea('

Cowpea"

Cowpea"

Cowpea''

Cowpea"

Specific



No

Yes

Yes

No

No



Cowpea"

Clover

Specific

Cowpea"

Cowpea"



Cowpea"

Cowpea"

cowpea

Cowpea

Specific

Specific

Lucerne



~



''A promiscuous species that will normally nodulate from native cowpea Rhizobium even

if not inoculated.



base status as in the Caribbean and Hawaiian islands. However, in

northern Australia areas of leucaena have grown quite satisfactorily in

moderately acid soils, an observation which indicates that lime may be

necessary only during the establishment phase.

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).



26



E. M. HUTTON



The successes with preinoculation and lime-pelleting have been with the

fast-growing acid-producing rhizobia and legume species like lucerne and

white clover. The calcium carbonate coating is stuck on with a harmless

adhesive of gum arabic or methyl cellulose. The calcium carbonate overcomes soil acidity and preserves the rhizobia on the seed. Most tropical

legumes with their tolerance to soil acidity require pelleting only for

preservation of their alkali-producing rhizobia. With the exception of

leucaena and perhaps silverleaf desmodium and glycine, extra alkalinity

added by lime-pelleting is unnecessary and may depress nodulation in

some tropical legumes. Rock phosphate is advocated as a pelleting

material for the tropicals, and preliminary results are promising.

The collection of Rhizobium at the Cunningham Laboratory comprises

large numbers of strains isolated from nodules collected from indigenous

legumes growing throughout the tropical world as well as strains from

other laboratories and from the nodules of the various field-grown cultivars. The strains are stored by absorbing them on unglazed porcelain

beads, which are then placed on slagwool pads in small McCartney

bottles half filled with silica gel desiccant (Norris, 1963). Rhizobium

strains are usually supplied to the farmer as peat cultures which are now

being used widely for inoculation of tropical legumes. Testing for effectivness is done by the Leonard bottle-jar technique in the glasshouse (Norris,

1964). Just how effective and persistent the inoculants are in the field is

not known in the case of the promiscuous legume species. Recently research on the various aspects concerning the ecology and field effectiveness of inoculant strains has been commenced at the Cunningham Laboratory using serotyping techniques. This may result in the selection of more

aggressive and persistent inoculant strains and so lead to better field performance of a number of the tropical legumes.

Heritable variation in nodulating ability was found in centro by Bowen

and Kennedy (1961), and it appears to be a feature in at least two other

tropical pasture legumes, greenleaf desmodium and glycine. In spite of

thorough inoculation with a fully effective strain of Rhizobium, yellow,

retarded, and poorly nodulated plants appear in populations of these

species. A study of the inheritance of nodulating ability in greenleaf

desmodium and glycine is now in progress at the Cunningham Laboratory. Since the plant dominates the symbiosis, genetical work aimed at

improving current cultivars must include a check of the nodulating ability

of the selections made from each generation. Unless this is done, improved agronomic types with poor field nodulation could easily be produced (vide Gibson, 1962).



TROPICAL PASTURES



VII.



27



Legume Nutrition Relative to Tropical Pasture Development



Unless plant nutrient deficiencies in the soil are corrected and the

legumes given adequate quantities of the various elements essential for

optimum growth, poor production will result from legume-based pastures.

Also, testing of all potential pasture species needs to be done in the

presence of adequate fertilizer. These important aspects are often overlooked in the rapidly developing countries of the tropics, with the result

that attempts to establish improved pastures often have been a failure.

On a highly manganiferous Low Humic Latosol in Hawaii, Younge and

Takahashi (1953) obtained a marked response to Mo in dry matter and

protein yields of thirteen lucerne varieties given adequate basal fertilizers

including phosphate, K, sulfate, and borax. Further work by Takahashi

( 1956) showed the importance of lime, phosphate, K, sulfate, borax, and

Mo in maintaining about 40% kaimi clover (D. canurn) with kikuyu- (P.

clandestinum), pangola-, or dallisgrass (P. dilatatum) in the humid lowlands of Hawaii. On the island of Kauai, revegetation of bauxite substrate (stripsoil) with and without return of 8 inches of topsoil was studied

by Younge and Moomaw (1960) after heavy dressings of all elements

thought to be deficient and planting a mixture of D.intortum, kaimi clover,

and pangolagrass. The controls without fertilizer were a failure, but topsoil and stripsoil (with extra P) in the first two years gave high dry matter

yields, particularly of D.intortum. Younge et al. (1964) summarized results from several old and recent experiments on the Hawaiian islands

of Oahu, Kauai, and Maui. D.intortum-pangolagrass adequately fertilized

with lime and N, P, K, maintains 30-40% legume and gives up to 20,000

Ib dry matter per acre per annum and a corresponding beef liveweight

gain of 800 Ib. Kaimi clover is tolerant of lower soil fertility and not as

productive as D . intortum, and both legumes respond markedly to P, K,

Mo, and Zn. The experiments also showed that lime, Mo, and Zn significantly increased seed yield of these legumes. These Hawaiian experiments demonstrate the importance of adequate nutrients, notably P and

Mo, for satisfactory growth and seed production of legumes in the tropics.

In northern Australia, the great arc of solodic and podzolic soils in

coastal and subcoastal areas from northern New South Wales to Cape

York Peninsula across the Gulf of Carpentaria to the Northern Territory

and Kimberleys of Western Australia are very deficient in P and S, both

vital to legume growth. A deficiency of Mo, an essential for functioning

of Rhizobium, occurs in a number of areas, but its extent is not known

at present.



28



E. M. HUTTON



The initial detailed research on soil nutrient deficiencies and nutrient

responses of legumes in coastal areas of northeastern Australia was done

by Andrew and Bryan (1955, 1958; Bryan and Andrew, 1955) in the

southern Wallum on very poor sandy acid soil near Beerwah, 40 miles

north of Brisbane. These soils are very deficient in P (3-6 ppm), Ca, and

K, as well as N. Depending on site, the limiting nutrients for plant growth

in descending order are P, N , Ca, K, S, Cu, Zn, Mo, and B. Effective

strains of rhizobia were obtained for white clover, P . luthyroides, and

the other test legumes which resulted in efficient nodulation and elimination of the need for N. Relatively low applications of calcium carbonate

promoted good legume growth, as the response was due to Ca nutrition,

not to the soil pH factor. Overliming could adversely affect pH and availability of elements like Cu and Zn. White clover needs more Ca than

silverleaf desmodium and responded significantly to soil additions of

Cu which did not increase growth of silverleaf. On the lateritic podzolic

soil type, maximum response of white clover to S occurred only when 200

lb of Ca per acre was applied. Under grazing and with adequate fertilizer,

white clover persists on the wet gley soils and not on the dry podzolics

whereas silverleaf persists on both soil types. For pasture establishment

on these poor southern Wallum areas, the fertilizer mixture needed per

acre comprises 5 cwt superphosphate, 5 cwt calcium carbonate, 1 cwt

potassium chloride, 7 Ib copper sulfate, 7 Ib zinc sulfate, 7 Ib borax, and

2 oz elemental Mo. This is a heavy initial dressing, but the subsequent

annual requirement is only 2 cwt superphosphate and 1 cwt potassium

chloride per acre. A similar fertilizer regime is needed to develop improved legume-based pastures in the northern Wallum extending in

Queensland from Maryborough to just north of Bundaberg (T. R. Evans,

1967). Altogether the sandy infertile coastal lowlands of the Wallum

cover some 2 million acres. Cost of developing improved pastures here

is high, but beef production is profitable because of a good rainfall (4065 inches), long growing season, and maintenance of a high stocking rate

of a beast per acre. The Wallum is only a small fraction of the vast area

in northern Australia awaiting development through improved pastures

(J. G. Davies and Eyles, 1965). Much of the area can be developed more

cheaply than the Wallum and requires only a suitable legume-based pasture and annual application of 1-2 cwt of superphosphate per acre, use

of Mo where deficient, and the occasional inclusion of a potassic fertilizer.

Following the preliminary Wallum work, Andrew ( 1960) found that

additions of sodium phosphate, potassium chloride, and calcium carbonate each increased the yield of white clover in a humic gley soil and

increased its P, K, and Ca contents, respectively. Yield of clover was



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