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Copyright 2005, Board of Trustees, University
Indian River Field Laboratory Mimeo Report IRL 66-2 -*
/ad March 10, 1966
6/ A DESCRIPTION OF TWO NEW SUMMER-GROWING LEGUMES
..? % 6 (e FOR SOUTH FLORIDA PASTURES > .
Albert E. Kretschmer, Jr./
Preliminary testing of sub-tropical legume species began at th6e'ndian River
Field Laboratory in 1956 and an expanded program started in 1960. About 200
varieties, including 21 genera and 41 species, have been or are being screenedL''
for Florida adaptability. Although this represents only a small number of the
total number of legumes that may be adaptable, good progress has been made in
finding several species that undoubtedly will be used in the future forage and
pasture programs in Florida.
Two of the most promising ones have been under small plot clipping tests in
pangolagrass, and tested under grazing in several commercial pastures. They are
discussed in more detail in the following paragraphs.
SIRATRO (Phaseolus atropurpureus DC.)
The original seeding of this summer-growing perennial legume in the United
States was made at the Indian River Field Laboratory on June 20, 1962. Some of
the original plants are still living. Tests at the Indian River Field Laboratory
have been confined to growth in established or establishing pangolagrass sod on
Immokalee fine sand that sometimes has a very high water table. Even though
growth and persistence of Siratro has been satisfactory to excellent on flatwood
soils, this legume's root system (tap root plus auxiliary roots from stolons)
seems ideally designed for moderately to well-drained soils.
Siratro is a somewhat stoloniferous, twining type legume that will climb
fences and grasses. In south Florida plants from early spring seedings will
produce seeds in the late fall. Seed production also will occur in the spring
in established stands. Summer seed production is insignificant, indicating a
short-day length requirement for flower and seed production. Seed production
the second and succeeding years should be better than the year of seeding.
Total seed production would depend upon the severity of the winter since Siratro
plant tops are defoliated or killed by heavy frosts or below freezing temperatures.
Little cold damage has been observed on tap roots or stolohs of plants five to six
months of age or older. It is not known how far north this legume can survive
winter temperatures but the method of regrowth from the crown area at or below
the soil surface should permit growth in all of Florida and in some portions of
the Gulf and adjoining States. This legume will spread as a result of natural
seed desemination, and moderate plant population increases can be achieved under
properly managed grazing conditions.
Siratro seeded to established pangolagrass does not compete as satisfactorily
as when seeded at the time of planting pangolagrass. It is not known what effects
the increasing density of pangolagrass will have on the vigorous Siratro plants.
However, the large Siratro stolons produced during the year of seeding, where
competition is small, should maintain a more vigorous plant population than where
1/ Associate Agronomist, Indian River Field Laboratory, Florida Agricultural
Experiment Stations, Ft. Pierce, Florida.
the Siratro seedlings do not.h.ve an-opportunity,to develop stolons because of the
already established grass.
A liming and fertilizer greenhouse experiment was instigated using virgin
Immokalee fine sand with a low nutrient status and a pH of 4.8. Results showed
the need of a minimum of 1 ton of hi-calcic lime a.id 60 pounds each of phosphate
(P205) and potash (K20) per acre for satisfactory growth initially. Additional
response to more.lime and phosphate.was indicated.
Established Siratro plants will survive under continued intense grazing but
will not add materially to thegrazing program and because of the lack of seed
production, plant populations .will not.increase. Under a rotational grazing
program, or one that permits adequate seed production in the fall,. tonnage. and
protein additions to the pasture from Siratro would be increased considerably.
Where Siratro is well established in pangolagrass or.Coastal bermudagrass,
fertilizer nitrogen can be used in the late spring to increase total grass
production without damaging the stand of Siratro.. This legume will grow up the
grass stems. Preliminary observations indicate that such a program would produce
high quality feed for hay, silage, or grazing.
The ability of Siratro to compete satisfactorily when seeded to established
bahiagrass or carpetgrass sods is doubtful. Seeding grass and legume simultane-
ously, however, would permit good establishment of Siratro and its competitive-
ness should be maintained for. several years.
The addition of Siratro to white clover-pangolagrass pastures appears certain
to add to the over-all production of quality feed without undue competition with
the white clover.
Dry weight yields and dry matter contents of Siratro-pangolagrass mixtures
are presented in Table 1. These were obtained from small-plot, replicated clipping
experiments. In one test the Siratro seedlings were transplanted to established
pangolagrass plots -that.had been disked once. Plants were grid-spaced to one
foot apart. In the second test both were planted simultaneously with Siratro
seeded at a rate of 10 pounds per acre. About 3.5 tons of the mixture were pro-
duced per acre per year compared to slightly more than 2 tons of similarly treated
pangolagrass receiving 30 pounds of nitrogen per acre in the fall. Crude protein
contents averaged about 7.5 percent compared to about 5.0 percent for pangolagrass
Because of the high cost of seeds, a seeding rate of about 1 pound per acre
should be used. The "cow-pea type" of inoculant at 2 to 4 times the manufacturers
recommendations should be used. In addition to the use of Siratro for cattle feed,
the seeds are relished by quail and other game birds.
Stylosanthes humilis HBK
The genus Stylosanthes contains about 25 annual or perennial species, some of
which are native to the United States. S. humilis has been used as a legume for
grazing and hay in Australian agriculture since the early 1900's, and is said to
be the only pasture legume of importance in the arid tropical areas of Australia.
S. humilis is a summer-growing, self-regenerating, annual. It has trifoliate
leaves and branched stems that are ascending or sometimes prostrate that can reach
a height of 30 inches or more. It competes well in pangolagrass, is tolerant of
acid and low fertility soils, but will grow well under soil conditions favorable
for white clover growth. It does not compete unfavorably with white clover stands
since vigorous S. humilis growth does not begin until June. It produces an abun-
dance of hard seeds beginning about the first of November (flowering can begin
about the first of September but maximum flowering occurs about October 1).
S. humilis stands have been maintained even under intensive grazing. However,
for maximum plant population increases care should be taken in the fall of the
initial seeding year to permit maximum seed production. Deferred grazing in the
fall permits maximum seed production, and a build-up of high quality reserve
winter feed that can be grazed or used for hay about the end of November.
The first successful stand of S. humilis at the Indian River Field Laboratory
was obtained in 1963. Since then several small commercial seedings have persisted
under soil conditions ranging from moist to excessively drained. It is believed
that S. humilis also can be grown successfully with Coastal bermudagrass and
possibly with carpetgrass and bahiagrass.
Yields, dry matter and protein contents of S. humilis-pangolagrass mixtures
are presented in Table 1. These were obtained from small-plot clipping tests in
conjunction with the Siratro experiments. Oven dry matter yields averaged about
4 tons per acre with average protein contents of about 8 to 12 percent in the
summer and fall.
Initial seedings of S. humilis should be made on well prepared soil limed with
a minimum of 1 ton per acre (virgin flatwoods soils). A minimum of 400 pounds of
0-12-12 per acre should be applied at seeding to virgin soils. If the grass is
fertilized at about the same rate of P205 and K 0 when planted no additional
fertilizer probably needs to be applied until the following year. Additional
fertilization with 400 pounds of 0-10-20 per acre per year in the spring should
be adequate unless white clover is included when the 0-10-20 should then be
applied in the late fall. Seeding rates of from 1 to 4 pounds per acre should
be used and "cow-pea type" inoculant should be used at a rate similar to that
Table 1. Yields, Dry Matter Contents and Crude Protein Contents of Pangolagrass,
Pangolagrass plus Siratro, and Pangolagrass plus S. humilis Mixtures
7/1/63 9/11/63 1/6/64 Total 7/1/63
(Seeded to Established Pangolagrass)
2360 2600 2860 7820 24.0
2000 3490 2160 7650 20.9
440 1420 3450 5310 20.3
of nitrogen per acre applied to plots in the fall of 1963 and 1964.
. 3 I