Group Title: Circular Florida Cooperative Extension Service
Title: Legume inoculation in Florida
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 Material Information
Title: Legume inoculation in Florida
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 3 p. : ; 28 cm.
Language: English
Creator: Hubbell, D. H ( David Heuston ), 1937-
Jones, D. W
Thornton, G. D ( George Daniel ), 1910-
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1991
Subject: Legumes -- Inoculation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references.
Statement of Responsibility: D.H. Hubbell, D.W. Jones and G.D. Thornton.
General Note: Cover title.
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Bibliographic ID: UF00014472
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6884
ltuf - AHR4417
oclc - 24153751
alephbibnum - 001639393


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SCircular 376

Legume inoculation in Florida
D.H. Hubbell, D.W. Jones and G.D. Thornton

Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida/ John T. Woeste, dean

What is legume inoculation?
Legume inoculation is the practice of introducing
specific bacteria into the soil with legume seed,
usually when planting. The bacteria belong to the
genera Rhizobium or Bradyrhizobium but are
commonly referred to as "rhizobia," "legume
bacteria" or "root nodule bacteria." They infect the
roots of leguminous plants a few days after seed
germination. Within one or two weeks, small
nodules appear on the roots as a result of these -',- c
infections. Mature nodules iay be round,t :i,,- r
cylindrical, or lobed, depending on the plant
species. JUL _2 4 1931

What is successful inoculation?
['" -'I, o 0' ,:
The presence of nodules on legume roots proves
the bacteria have successfully eifectedTh i~oo-its
This is important because the rhizobia living in the
nodule enter into a "symbiotic" or mutually bene-
ficial relationship with the plant. The plant and
the bacteria work together to reduce or "fix"
nitrogen gas (N2) from the air into ammonium
(NH4+) in the plant root. As ammonium, it can be
used by both the bacteria and the plant as a nut-
rient for growth. A pink color within the nodule in-
dicates nitrogen is being fixed. This can be observ-
ed by crushing or slicing nodules which are about
one week old. Very young nodules have a white
interior and very old nodules have a brown interior.
Little or no nitrogen is fixed in these nodules.

Why is inoculation important?
The ability of the plant-bacteria combination to
"fix" and use an otherwise unavailable form of
nitrogen is of considerable economic importance to
farmers. The symbiotically-fixed nitrogen
supplements soil nitrogen, which is low in most
soils. This is especially true for the mineral soils of
the Southeastern coastal areas, where leaching,

Professor, department of Soil Science. Professor, Department
of Agronomy. Professor, Department of Soil Science; IFAS,
University of Florida, Gainesville, FL 32611.

erosion and removal of crop residues have severely
reduced the supply of soil nitrogen.
Nitrogen is a key element for living cells. It is
an essential part of protein, the building block of
plant and animal tissue. Nitrogen is the plant
nutrient that most often limits crop growth, for two
main reasons. First, plants need more nitrogen
than other nutrients in order to achieve good
growth. Second, soil nitrogen is constantly being
lost through run-off, leaching, denitrification and
removal of nitrogen-containing crop residues from
the sqil. Denitrification is the process of changing
plant'available nitrate nitrogen to atmospheric
nitrogen, which then diffuses as a gas to the
atmosphere. Denitrification results in a loss of soil
nitrogen and is opposite in effect to the process of
"nitrogen fixation" carried on by rhizobia.
Soil nitrogen is replenished primarily from
fertilizers and nitrogen fixation. Nitrogen
fertilizers may be inorganic materials such as urea,
ammonium nitrate or ammonium sulphate. Nitro-
gen fertilizers are immediately available for plant
uptake. They are rather expensive because of the
process involved in their manufacture.
As a soil residue, "organic nitrogen," or rhizobia-
fixed nitrogen, is not immediately available for
plants. Numerous kinds of soil organisms must
first decompose the organic residues. This results
in a slow but continuous release of inorganic
nitrogen which can be used by growing plants.
Because of the slow release, nitrogen is not lost
through leaching.

Do all leguminous plants fix
A leguminous plant is one that has seed pods.
Beans, peas, soybeans, lupine, peanuts, and
cowpeas are common legumes with prominent seed
pods. Other legumes with less conspicuous seed
pods are clover, lespedeza, beggarweed, crotalaria,
hairy indigo, trefoil, alfalfa, and vetch.

Almost all leguminous plants have the ability to
form nodules when inoculated with the right kind
of root-nodule bacteria. A few exceptions are the
honey locust, redbud, and Kentucky coffee tree.
Leguminous plants differ in the amount of
nitrogen they return to the soil. Obviously, crops
such as peanuts that are harvested for nuts and
hay return little nitrogen to the soil. Frequently,
such crops deplete the soil of some nitrogen because
the nodules fail to fix all of the nitrogen needed by
the plant. Other crops, such as soybeans harvested
for seed, or lespedeza harvested for hay, leave a
portion of the plant on the land as stubble. These
crops may fix as much nitrogen as that removed in
the harvested crop, leaving the soil nitrogen at its
original level. Still other crops, such as clover
pastures and hairy indigo, may add considerable
amounts of nitrogen to the soil. Mature animals on
a legume pasture leave most of the nitrogen in the
land. The largest increases in soil nitrogen are
obtained when the entire plant is returned to the
soil as full grown, succulent green manure. Some
excellent green manure crops, with the approxi-
mate amounts of nitrogen fixed per acre, are as
follows: lupine, 75 pounds; crimson clover, 80
pounds; hairy indigo, 70 pounds; crotalaria, 72
pounds; cowpeas, 86 pounds.

How can you successfully
Years ago, legume bacteria were introduced into
new areas by using soil from a field where desired
legumes had grown successfully the previous
season. This is now unnecessary. Commercial
inoculants of legume bacteria are now available
from seed dealers. These inoculants are a mixture
of bacteria selected for their ability to "fix" large
amounts of nitrogen in a particular legume or
group of legumes. This helps insure that different
legume species or varieties of the same legume
grown in different areas, where conditions such as
temperature, moisture, pH, and nutrient status
may vary, can be successfully inoculated with the
same bacteria.
Each container of commercial inoculant has a
written set of instructions. Check the following
items carefully: the age of the culture as shown by
the date on the container; the list of plants the
culture will satisfactorily inoculate; the quantity of
seed for which the contents of the container are
intended; and directions for applying the inoculant
to the seed.
Because inoculants are PERISHABLE, purchase
the inoculant from a reliable dealer who can assure

you the material is fresh and has been stored in a
cool place. Legume bacteria are killed by excessive
drying and high temperatures. For this reason the
expiration date does not always insure a strong and
viable culture. Therefore, not only the AGE of the
culture, but also the STORAGE CONDITIONS
prior to inoculation (in the warehouse and on the
retailer's shelf) are vital factors to be considered.
When the seeding date is near, it is a good idea
to buy the seed and inoculant at the same time.
This insures having the culture on hand when the
weather is favorable for planting. It is the buyer's
responsibility to be sure he is getting the proper
inoculant. Inoculant should be stored in a
refrigerator or in an air conditioned room if it is not
used immediately.
NOTE: TWICE the manufacturer's
recommended amount for large seeded legumes and
FIVE TIMES the recommended amount for small
seeds have given more satisfying results under
Florida's soil and climate conditions. Hot, dry
weather kills legume bacteria. Using extra
inoculant, under cool, moist conditions if possible,
insures against inoculation failure.
Care of inoculated seed. Plant legume seed
as soon as possible after inoculation. Seed should
never be exposed to direct sunlight or
allowed to dry before planting. Never inoculate
more seed than can be conveniently planted
within a few hours. If there is a delay in seeding
for more than two or three hours, keep the seed
moist and cool. If the seed becomes excessively dry
for any reason, REINOCULATE. It will pay.
Seedbed preparation. Plant inoculated seed
in well-prepared, moist soil. To insure quick
germination and prevent the death of inoculant
bacteria by drying, roll the planted soil with a
cultipacker equipped with a seeding attachment. It
is often necessary to plant clover seed in grass sod.
This makes it hard to secure good germination and
satisfactory inoculation. The chances of obtaining
inoculated clover will increase if the grass is closely
clipped and the soil surface scarified by light
disking just before or at the time of seeding. It is
beneficial if seeding can be done during light rains
and cloudy skies. The rain keeps the ground moist
until the seedlings are established and nodulation
takes place.
Seed treatments and fertilizers. Many
pesticides are toxic to legume bacteria. Although
some pesticides may be non-toxic to legume bacte-
ria, chemicals and inoculant should not be used
together in planting. If it is necessary to plant
pesticide-treated legume seed in large scale opera-

tions, the soil may be "preinoculated." The
inoculant is mixed with moist soil, moist sawdust,
or other inert material and is then incorporated in
the soil before seeding. This may be carried out on
plowed fields at the last harrowing for weed control
and final preparation just before seeding.
Inoculated seed should not come in contact with
caustic lime, acid fertilizers, or fertilizers
containing chemical salts. Inoculated seed can mix
in the drill spout with materials such as
superphosphate and basic slag. Ordinarily,
concentrations of fertilizer in the soil that do not
affect seed germination or injure seedling roots will
not harm the root-nodule bacteria. However,
mixing fertilizer with inoculated seed should be

How do you choose an
Several types of legumes may be effectively
nodulated by a single species of root-nodule
bacteria. Plants nodulated by different species of
bacteria are called CROSS INOCULATION
GROUPS. Commercial inoculant containers are
clearly labeled with the proper Cross Inoculation
Group designation. It is the buyer's responsibility
to request inoculant for the Cross Inoculation

Alfalfa group
alfalfa bur clover
sweetclover black medic
Cowpea group
cowpea lima bean
crotalaria pigeon pea
lespedeza partridge pea
peanut mung bean
kudzu hairy indigo
alyce clover Aeschynomene
beggarweed Stylosanthes humilis
velvet bean
Lupine group
blue lupine white lupine
yellow lupine serradella
Soybean group
Clover group
Berseem clover crimson clover
white clover subterranean clover
red clover other true clovers
Pea and vetch group
field pea sweet pea
garden pea rough pea
Austrian winter pea (Singletary, Caley)
common vetch tangier pea
monantha vetch
Bean group
garden bean scarlet runner bean
Trefoil group
birdsfoot trefoil

Group which includes the legume he wishes to
plant. The more commonly recognized groups are
as follows:
Frequently, strains of bacteria effective on one
member of a group are ineffective on other
members of the same group. An ineffective strain of
bacteria is "parasitic:" it will nodulate a particular
plant but will fix little or no nitrogen. Good ex-
amples of this are in the clover and trefoil groups.
In the clover group, effective strains of bacteria
isolated from crimsom clover are ineffective on
white clover and vice versa. Bacteria isolated from
either big trefoil or birdsfoot trefoil may be totally
ineffective on one or more group members.
Therefore, satisfactory group cultures can be
prepared by combining strains which have been
proven effective on all members of the same group.

Why does inoculation fail?
There are times when inoculation fails. Some
possible causes of failure are the following:
* Use of wrong inoculant. It is the buyer's respon
sibility to know the type of inoculant he needs, to
request it specifically, and to ascertain that he
has received what he requested. If in doubt
about the type of inoculant required he should
consult his County Extension Director.
* Unfavorable soil conditions. In general, soil
conditions (other than high soil N levels) which
favor plant growth also favor the processes of
nodulation and nitrogen fixation.
* Use of dead inoculant. Although unlikely,
inoculant may be dead due to faulty manufac-
ture. It is more likely to be the result of poor
shipping or storage conditions before purchase.
In particular, exposure to high temperatures,
even for very brief periods of time, or to direct
sunlight, may severely reduce the success of
M Faulty handling of inoculant after purchase.
Inoculant must be transferred and stored under
cool conditions. Pay careful attention to the in-
oculation procedure previously outlined.
NOTE: Excessive heating or drying of the in-
oculant at ANY time before use will result in
inoculation failure.

What are the benefits of
M Improved quality of forage. The protein content
of pasture and hay is increased by the presence

of inoculated legumes.

* Increased animal gains. Higher protein content
can improve legume taste. This results in
increased consumption of total digestible nutri-
ents by the animal. Compared with other
forages, the leguminous plants are higher in
calcium, phosphorus, and other essential growth
* Added soil nitrogen. An inoculated legume crop
may add anywhere from 50 to more than 100
pounds of nitrogen per acre to the soil. The
amount depends on the soil reaction, crop size,
effectiveness of the fixation process, portion of
the crop left on the land, phosphorus and potas-
sium levels in the soil, and amount of nitrogen
already available in the soil.
* Increased subsequent crop yields. Yields of corn
and other crops have been doubled and even
tripled by growing them in rotation with legumi-
nous green manure crops.
* Improved soil conditions. Properly nodulated
legumes are rich in nitrogen. They often contain
several times as much nitrogen as was with-
drawn from the soil. The presence of certain
high-nitrogen compounds in legumes causes
them to decompose rapidly. This leaves finely
divided organic matter in the soil which im-
proves soil moisture, nutrient retention, and soil
* Reduced erosion. Legumes inoculated with
effective strains of root-nodule bacteria thrive in
soils poor in nitrogen. If adequate amounts of
lime, phosphate, and potash are present, water
and soil losses may be reduced to a minimum by
growing legumes. Properly inoculated kudzu,
beggarweed, crotalaria, hairy indigo and peren-
nial lespedeza are exceptionally well adapted for
this purpose.

Growing factors of legumes
Although proper inoculation is the key to eco-
nomic production of legumes, it alone cannot insure
success. Other essential factors are:
n Good seedbed preparation.

* Use of lime where needed. (Usually not required
for legumes of the Cowpea Group).
* Adequate supply of phosphorus and potassium.
* Use of micronutrients where needed. Many
Florida soils fail to support the satisfactory
growth of legumes. This can be overcome by
supplementing with copper, manganese, zinc,
boron, or a combination of these micronutrients.
Follow the recommendations of your county
extension agent.
* Selection of the kind and variety of legume best
suited for the soil conditions and area within the

Legume and inoculation
There are several current publications on
growing various legume crops in Florida. The
publications listed below may be obtained from
County Extension Offices or by writing to: Publica-
tions Distribution Center, IFAS Building 664,
University of Florida, Gainesville, FL 32611.
Soybean production guide (Circular 277E)
"Osceola" White Clover (Circular S-311)
"Florida 77" Alfalfa and Recommended Practices for its
Production (Circular S-191)
"Florigraze" Rhizoma Peanut, a Perennial Forage Legume
(Circular S-275)
"Arbrook" Rhizoma Peanut, a Perennial Forage Legume
(Circular S-332)
Hairy Indigo, a Summer Legume for Florida (Circular S-316)
Production and Utilization of the Tropical Legume
Aeschynomene (Circular S-290)
"Florida" Carpon Desmodium, a Perennial Tropical Forage
Legume for Use in South Florida (Circular S-260)
Stylosanthes humilis, a Summer-growing, Self-regenerating
Annual Legume for Use in Florida Pastures (Circular S-184)
Phasey Bean, a Summer Legume with Forage Potential for
Florida Flatwoods (Circular S-330)

Woeste, director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8
and June 30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and
institutions that function without regard to race, color, sex, handicap or national origin. Single copies of extension publications (excluding 4-H J
and youth publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state
purchasers is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611 .......... 1
Before publicizing this publication, editors should contact this address to determine availability. Printed 6/91.

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