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Copyright 2005, Board of Trustees, University
ARC Research Report RL-1981-2
FORAGE RESEARCH AT THE
AGRICULTURAL RESEARCH CENTER
FORT PIERCE, FLORIDA
ALBERT E, KRETSCHMER, JR.,
JOHN B. BROLMANN,
GEORGE H. SNYDER,
RONALD M. SONODA,
ROBERT C, BULLOCK
Institute of Food and Agricultural Sciences
University of Florida
The University of Florida's Agricultural Research Center, Ft. Pierce
(ARCFP) is located at 27025'N latitude and 80024'W longitude. Rainfall
occurs predominately in the summer in the tropical-subtropical area of
Penisular Florida, south of a semicircular line (Figure 1) between latitudes
280 and 290N. Monthly rainfall averages (mm) and percent rainfall per month
for a 28 year period at the ARCFP are as follows:
Jan. Feb. Mar. Ap. May June July Aug. Sept. Oct. Nov. Dec. Total
Avg. 55 75 77 62 136 190 185 168 204 177 57 52 1438
% 3.8 5.2 5.4 4.3 9.4 13.2 12.9 11.7 14.1 12.3 4.0 3.6
The average number of days receiving greater than 5, 25, and 50 mm rainfall
are presented below.
Jan. Feb. Mar. Ap. May June July Aug. Sept. Oct. Nov. Dec. Total
5 2.8 3.1 3.4 3.1 5.0 7.0 7.8 7.4 8.5 5.9 2.3 2.7 59.0
25 0.5 0.8 0.6 0.6 1.3 2.2 2.2 2.2 2.3 2.1 0.6 0.5 15.9
50 0.1 0.3 0.3 0.1 0.7 0.7 0.5 0.4 0.6 0.8 0.1 0.1 4.7
The underground aquifer supplies artesian or pumped water in many areas of
Penisular Florida to supplement forage requirements during the spring period.
Most pastures in south Florida are planted on Spodosols (having an organic hardpan
from near the surface to about one meter below the surface) interspersed with
Entisols (Figure 2) (no hardpan zone). Internal and external drainage is poor.
There is periodic flooding of large areas during periods of extended heavy preci-
Mean maximum and minimum monthly temperature averages (oC) at the ARCFP are
Jan. Feb. Mar. Ap. May June July Aug. Sept. Oct. Nov. Dec.
Max. 23 25 26 28 30 32 32 33 32 29 27 24
Min. 10 12 13 16 19 21 22 23 22 19 16 12
Areas to the north and west of the ARCFP are cooler in the winter and some-
what warmer in the summer. All except the extreme southern portion of the region
is subjected to several frosts during the December-March period, with severe
freezes (-40 to -60C) occurring every several years particularly in the northern
These climatic factors result in an uneven seasonal growth pattern of
tropical forages, with about 70 to 80% occurring in the six months of May-October.
This growth period has been extended, through judicious use of fertilizer and
water control, and particularly through the development of several grasses
that grow more rapidly in the cool season than does 'Pangola' digitgrass
(Digitaria decumbens) and the bahiagrass (Paspalum notatum). These grasses
are 'Bigalta' limpograss (Hemarthria altissima), star bermudagrasses (Cynodon
nlemfuensis), 'Transvala' digitgrass (Digitaria decumbens), and 'Taiwan' digit-
grass (D. pentzii). Planted areas of these grasses are small compared with
those of Pangola and particularly those of 'Pensacola', 'Argentine', and,
High quality temporary pasture of annual ryegrass, oats, red and berseem
clovers, and alfalfa have been used for winter-spring grazing in special instances,
when irrigation is available. White clover ('Louisiana S-1', 'Nolins Improved',
etc. which commence.flowering in late February and March), is the best, most
persistent, cool season legume, although production of dry matter is low until
February or March. Summer survival by white clover is not uncommon in many areas.
These pastures are best used for brood cows and recently "dropped" calves to
insure rapid "recycling".
During the past 20 years there has been increasing interest in the use of
tropical legume-based pastures. Alysicarpus vaginalis, Indigofera hirsuta, and
more recently Aeschynomene americana, annuals, have been used successfully on a
commercial scale. There are pastures of grass-Stylosanthes humilis and Macrop-
tilium atropurpureum but only on a limited scale, mainly because of high summer
water tables and seed harvesting problems. 'Florida' carpon desmodium (D.
heterocarpon) released in 1979 is the first perennial legume that appears to have
most of the attributes sought for in a tropical legume, ie., moderate animal
acceptability, persistence under grazing, tolerance to moist and periodic flooded
areas, concentrated seed set, and relatively easy commercial seed harvest.
Commercial harvesting was commenced about four year ago and results of grazing
and legume persistence have been rewarding.
Because of the climate, successful commercial use of tropical legumes
in south Florida, and the research emphasis, the Agronomy section of ARCFP
began to maintain a formal germplasm bank. It is one of the largest in the
world and consists of several thousand accessions, most of which are in long-
term storage under refrigeration. Besides seed collection trips to various
tropical American countries, seeds have been exchanged with germplasm centers
in Australia, Colombia, the USDA, and elsewhere. In addition, theiSouthern
Regional Plant Introduction Center under the direction of Mr. Gilbert R. Lovell
has requested that we help them by increasing tropical legume seed supplies of
their USDA, PI numbered accessions. This has been an ongoing project for
several years. The ARCFP frequently distributes tropical legume seeds to other
Research Centers in Florida and elsewhere upon request for additional testing.
In conjunction with the germplasm bank, a herbarium of several hundred specimens
is maintained and being amplified as new accessions are initially evaluated.
Evaluation consists of three general steps which may be separate or closely
meshed. They consist of initial evaluation of new collections, selections, or
breeding lines to determine flowering patterns; and seeding ability, growth habit,
persistence, and resistance to drought, flooding, cold temperatures, insects,
and diseases. Secondary evaluation consists of clipping experiments in grass
mixtures, fertility and lime requirements, and persistence under grazing in
commercial ranches. The Legume Breeder and Agronomist work in close association
with Drs. Ronald M. Sonoda (Plant Pathologist, ARCFP), George H. Snyder (Soil
Chemist, AREC-Belle Glade) and Robert C. Bullock (Entomologist, ARCFP) on
problems associated with selection and evaluation in various stages of legume
The ARCFP will have a computer terminal in 1981 and the names and other
pertinent data of the more than 5000 tropical legume accessions will be
placed on tape in a retrievable manner to simplify the system of obtaining
necessary data and to better serve the needs of Florida and other researchers
through seed distribution.
O Gainesville '
25- 60 I
E = Entisols
Figure 2. Generalized map of Soil Orders found In Florida.
Figure 1. Distrbution of cattle population In south Florida.
Albert E. Kretschmer, Jr., Agronomist
Experiments now in progress or contemplated this year are:
1. Initial Evaluation (single row, unreplicated)
a. First and Second years -- about 600 accessions (including 125
Leucaena spp.) for seed increase for USDA, Southern Regional Plant
Introduction Center, Experiment, Georgia.
b. Second year -- about 530 newly introduced legumes, including 261
collected in southern Mexico in 1980 and a total of 196 Aeschynomene
c. First year -- 140 native Glycine spp. collected or introduced by
Dr. T. Hymowitz, Illinois University (Urbana).
d. Third year -- 100 Arachis hybrids obtained from Dr. W. C. Gregory,
North Carolina State University, retired.
e. Third year -- four ranchers' fields under various grazing management;.
about 150 widely diverse accessions previously selected from other
f. First year -- seed increase for 12 "Jicama" (Pachyrrhizus spp.)
2. Secondary Evaluation (replicated)
a. Third year -- same legumes as in "le", in mixtures with Pangola digit-
grass in small-plot clipping experiment.
b. First year -- plant spacing experiment with Jicama for biomass pro-
3. Completed except chemical and statistical analysis -- yield response of
'Florida' carpon desmodium (D. heterocarpon) to 0, 20, 60, 100 kg/ha of
P and 0, 200, 1000, 2000, 3000, and 4000 kg/ha of lime aragonitee) in
4. Third year -- persistence of carpon desmodium on native "flatwoods"
pasture (four locations) at low (300 kg/ha lime and 50 kg/ha of triple
superphosphate) and high (2000 lime and 200 triple superphosphate)
aragonite and P rates in all combinations.
Several species appear to be worthy of further testing. They include:
Aeschynomene villosa, A. americana (perennial type), A. elegans, A. evenia,
A. paniculata, and A. histrix; Desmodium barbatum and D. heterocarpon; a
Centrosema virginianum and C. pascuorum; a Vigna caracalla; two Zornia
latifolia; Calopogonium mucunoides; and a perennial peanut (Arachis sp.).
Of these, seeds of perennial peanut, will be increased in 1981 under the
direction of Dr. A. J. Norden, Peanut Geneticist, Gainesville. This high
seed producing introduction was collected in standing water in the Pantanal,
Mato Grosso, Brazil. Also it can be propagated vegetatively. Preliminary
in vitro digestibilities were as high as 74%. Its tolerance of high water,
yet ability to withstand the spring droughts, and persistence under initial
grazing demonstrations, make it one of the best possibilities for early
John B. Brolmann, Legume Breeder
Stylosanthes is considered a very promising legume for pasture use in
the tropical and sub-tropical areas of the world. In south Florida, as in
much of the subtropics, pasture growth becomes limited by low winter temper-
atures, spring drought, and periodic summer floodings. In Florida, work on
the improvement of this species began in the early 1970's with the intro-
duction, collection, and screening of many ecotypes.
At the ARCFP, selection is directed towards development of more cold
tolerant, flood tolerant, and early flowering styles.
Native Stylosanthes hamata types recently collected in south Florida
may have some desirable characteristics with respect to cold and drought
tolerance. In Florida over one hundred ecotypes have been collected from
along the Atlantic coast. S. hamata is well adapted to these calcareous
soils with high pH (available Ca 15,000 92,000 kg/ha; pH 6.5 8.8).
It has a deep root system which guarantees survival in seasons of extreme
drought, and it flowers almost year round with heaviest seed production in
December and January. Generally, the growth of most native ecotypes is
restricted to the coastal area, however, several very vigorous types which
have been isolated are also adapted to the more acid flatwoods soils. The
search for new types continues. Progeny studies at the ARCFP indicates
that most S. hamata ecotypes are very homogeneous and self-pollinating.
Ecotypical differences in the response to yield and frost tolerance has
been demonstrated in field experiments. The tetraploid ecotypes (2n=40)
had greater cold tolerance and generally yielded more forage than the
diploids (2=20). Some diploid ecotypes yielded 15 times more than other
A natural interspecific cross between a tetraploid native S. hamata
and S. scabra has been described. This hybrid is extremely vigorous and
highly tolerant to Colletotrichum gloeosporioides. Progeny studies, which
are now in the F-5 stage indicate increasing homogeneous plant material.
The F-l plants were extremely heterogeneous in nature and a large percent-
age showed susceptibility to Colletotrichum. The F-4 generation was more
vigorous than the F-3 plants and had greater disease resistance.
For continuous improvement and development of-new varieties, a know-
ledge of cross and self fertility relationship is required. Stylosanthes
ecotypes which are predominantly cross pollinated will show an in-breeding
depression when self pollinated. Experiments at the ARCFP have shown that
open pollinated clones of S. guianensis produced progenies that yielded 3
to 4 times as much dry matter as progenies from self pollinated clones.
When conditions become unfavorable for cross pollination during the colder
winter months (less active bee pollination) in-breeding depression can be
expected, resulting in less vigorous progenies. This is another reason
why early blooming types should be selected.
Plant persistence is .one of the most desirable characteristics for
selection. Therefore, breeding lines at Ft. Pierce are screened by
various types of selection pressure, and persistence is tested under
suboptimal conditions to develop more flood and cold tolerance types.
Recent experiments, indicated that a S. erecta was the most flood tolerant
species. Greatest persistence was found for S. scabra which was planted in
Pangola digitgrass eight years ago, and still maintains an excellent growth.
The most cold tolerant species was S. guianensis cv. Oxley.
Persistent hybrids were also isolated. These extremely vigorous types
produce very little seed. Seed fertility however, was successfully increased
through further progeny selection.
A major consideration in selecting styles is the ability to produce
sufficient seed for regeneration and variety release. The percentage hard-
seedness is important in areas where seed dormancy is required to escape
possible damage during periods of drought or frost. In Florida, for instance,
a seed dormancy period of at least 2 months will be required to escape
possible freeze damage to seedlings. There is little dormancy in the native
S. hamata type, probably explaining why these ecotypes have not moved further
north in Florida. Early flowering S. guianensis types have already been
developed at ARCFP. These selections will not bloom later than mid-September
and will set seed before winter.
In other studies at the ARCFP it was shown that germination of hard
seeds can be improved by subjecting seeds to a dry-heat treatment, and
alternating temperatures of cold and heat. Stylosanthes trials are also
being conducted at several commercial sites and other Research Units.
Dr. George H. Snyder, Soil Chemist
South Florida mineral soil pasture lands are dominated by Entisols and
Spodosols (Figure 2). These soils generally are coarse textured, acid, in-
fertile, and low in organic matter and water holding capacity (Table 1).
They are poorly drained because of their low-lying position and often are
waterlogged or even flooded during the summer rainy period. However they
can be drained fairly readily if sufficient ditches, canals and pump are
provided. In many cases these same devices, sometimes augmented with wells,
are used for irrigation during the winter and spring dry seasons.
To some degree compensating for the acidity and infertility of these
soils, is the small quantity of Al, Fe and Mn that might limit production if
present at higher toxic levels. Consequently, with proper liming and fertili-
zation, excellent pastures can be produced in this region. Pasture fertility
studies at the ARCFP have emphasized management of N fertilization for grass
production during the cool season (for direct or deferred grazing). For
tropical legumes the lime and P requirements are being determined. Fall N
fertilization studies have revealed an inverse relationship between forage
production and quality (crude protein) as fall N fertilization is delayed
(Tables 2 and 3). Late N fertilization studies have shown that crude protein
can be increased in standing forage by N fertilization during the winter,
even though growth is limited by temperature. Work conducted at the ARCFP
has also shown that tropical legume-grass mixtures can be used to supply good
quantities of fall-winter forage with adequate protein content in the absence
of N fertilization. Thus ranchers have several options for producing forage
of sufficient quantity and quality for winter season use.
In contrast to some research work presented from other tropical research
centers, tropical legumes in these soils have been found to respond to liming
up to at least 2000 kg/ha (Figure 3). Phosphorus also is important for
legume establishment and production in south Florida pastures. Maximum
production occurs at phosphorus rates of 40-80 kg P/ha, depending on species
Table 1. Typical profile of a Florida Spodosol as synthesized from statisi-
cal data on 34 pedons.
Horizon Depth Sand Silt Clay 0.1 0.33 15 pH saturation CEC OM
CM -------%-------- ----% vol---- % meq/100g %
Al 0-15 94.0 4.5 1.5 13 11 3.5 4.7 30 7 3.5
A2 15-65 97.0 2.0 1.0 3 2 1.5 5.1 50 1 0.3
B21h 65-83 92.0 4.0 4.0 15 14 4.0 5.0 15 10 3.5
B22h 83-103 94.0 3.0 3.0 6 6 2.0 5.3 20 5 2.0
B3 103-133 94.5 2.5 3.0 6 3 1.5 5.6 40 2 0.4
Table 2. Pangola
Date of mowing
digitgrass production and crude protein content during 91 day
following mowing and nitrogen fertilization (112 kg/ha) on
dates in the fall.
and fertilization Yield: Protein
(month, day) (kg/ha) (%)
September 17 3840 2.9
October 1 5400 5.0
October 15 4360 9.1
October 29 2250 14.6
Table 3. Pangola digitgrass production on January 16, following mowing and
nitrogen fertilization (70 kg/ha) on various dates in the fall of
the previous year.
fertilization Yield Protein
(month, day) (kg/ha) (%)
August 2 7670 3.4
August 31 4540 3.4
October 3 2690 5.1
October 31 810 6.1
/ --- -- --\'
Yield response of siratro, desmodium, stylo
and centro to lime, with 45 kg P/ha.
DISEASES OF TROPICAL FORAGE PLANTS
Dr. Ronald M. Sonoda, Plant Pathologist
Plant diseases reported on tropical forage plants are relatively few
(5). With the current increase in use of many of these newly introduced
crops, the impact of diseases is sure to increase. The objectives of our
work on diseases of tropical forage at the ARCFP are to develop means of
managing diseases where a disease occurs in a forage crop used on a commer-
cial basis and to have continual input in the screening and developing of
new varieties or cultural types of forage plants to reduce the possibility
of developing and releasing disease-prone types.
The current work consists of identifying diseases caused by fungi,
bacteriaviruses, nematodes and physiological factors; determining the
potential effect of these diseases under field conditions' and learning to
manage diseases with potential impact on promising Florida lines which
usually entails searching for resistance or tolerance to most of the diseases
with high impact.
Diseases which have resulted in significant losses in forage or quality
of the more promising lines for Florida include:
1) Diseases of Macroptilium atropurpureum; Rhizoctonia solani foliar
blight (3); a mosaic incited by a potyvirus (4); and rust incited by Uromyces
2) Diseases of Stylosanthes spp.; Colletotrichum gloeosporioides, incitant
of anthracnose can cause severe leaf and stem damage on some accessions (7).
Most native Florida Stylosanthes hamata with 2N=20 chromosomes are highly
tolerant. Native S. hamata with 2N=40 chromosomes are all moderately suscept-
ible (2). Experiments in the field indicate that significant losses in yield
in plantings of S. hamata with 2N=40 chromosomes (6).
3) Some Desmodium heterocarpon are highly susceptible to root knot
nematodes(l). Resistance to this organism is present in other accessions.
4) Minor leaf-spotting diseases have been observed on other genera and
species of grasses and legumes, but none of these diseases appear to have
high impact on grasses and legumes currently being developed. Virus diseases
may be very important as virus symptoms have been noticed on a-few plants
of various legumes and grasses.
1. Kretschmer, A. E., Jr., R. M. Sonoda and G. H. Snyder. 1980. Resistance
of Desmodium heterocarpon and other tropical legumes to root knot
nematodes. Tropical Grasslands 14:115-120.
2. Lenne, J. M. and R. M. Sonoda. 1981. Effect of Colletotrichum gloeo-
sporioides on yield of Stylosanthes hamata. Phytopathology (accepted
3. Sonoda, R. M. 1980. Reduction of forage yield of Siratro by Rhizoctonia
foliar blight. Plant Disease 64:667.
4. Sonoda, R. M. 1977. Effect of a mosaic virus on Siratro and other
Macroptilium atropurpureum accessions. Soil and Crop Sci. Soc.
5. Sonoda, R. M. 1975. Identifying and evaluating diseases of tropical and
subtropical forage crops. Soil and Crop Sci. Soc. Fla. 34:156-158.
6. Sonoda, R. M. and J. B. Brolmann. 1980. Differences in susceptibility
of Stylosanthes hamata to Colletotrichum gloeosporidides. Plant
7. Sonoda, R. M., A. E. Kretschmer, Jr. and J. B. Brolmann. 1974. Colleto-
trichum leaf spot and stem canker of Stylosanthes spp. Tropical
Agriculture, Trin. 51:75-80.
Dr. Robert C. Bullock, Entomologist
The ARCFP's program evaluating forage legumes for use in Florida pasture
improvement has lacked information on the influence of pest and beneficial
arthropods on the plant species being investigated. Literature on management
of arthropod.pests of forage legumes is meagre and of little value to the
current screening program for jointvetches (Aeschynomene spp.) so the Center's
entomologist has been recruited to assist in developing a more comprehensive
evaluation of plant material being considered for introduction.
To detect and identify all arthropods living in pure stands of legumes
as well as legume-grass mixtures and determine economic importance to
survival and productivity of plants. Develop management practices that will
suppress pest activity below economic damage threshold.
Important Past Findings
A number of beneficial arthropods, mostly spiders, have been identified
and one very important lepidopterous pest: the Gelechiid leafbinder Evippe
sp. All Aeschynomene accessions have been evaluated for resistance to Evippe
attack and a control program developed to protect A. americana (Tables 4, 5,
6, and 7).
The influence of the defoliating caterpillars, Selenis monotropa Grote,
Anticarsia gemmitalis Hubner, and Heliothis virescens Fab. on plant productivity
must be determined. Data gaps in Evippe sp. life history must be filled.
Identity of arthropods on other legumes must be made.
Table 4. Susceptibility of Aeschynomene introductions during initial
evaluation (1980) to leaf binding attack by the microlepidop-
teran Evippe sp. (Fam: Gelechiidae).
+ Data obtained during October 1980.
Number of leaves per hundred
Table 5. Susceptibility of Aeschynomene introductions (1979) to microlepidopteran
leaf binder attack in Pangola digitgrass mixtures.
Mexico PI 296044
Brazil PI 420316
Brazil PI 420319
histrix var. densiflora
L.S.D. 0.05 26.3
L.S.D. 0.01 34.9
+ Data obtained on November 16, 1979. Number of leaves per hundred leaves
Table 6. Susceptibility of Aeschynomene introductions (1980)
binding attack by microlepidopteran Evippe sp (Fam:
Gelechiidae) in Pangola digitgrass mixtures.
+ Data obtained on September 26, 1980.
Number of leaves per hundred
Table 7. Control of the Gelechiid leafbinder, Evippe sp. on American jointvetch.
per 378.5 1
Aug Sep Oct Nov Sep
Percent bound leaves
seen on indicated dates:
per 30.5 cm. of stem
AI Product 24 21-25 5 19 2 14 9 18 30 Pods
+ Ortho X-77
* Ortho X-77
SIR 8514 25w
SIR 6514 25W
Proxol 80 SP
x x x x
1.2 1.0b+ 6.8d 13.hb
40 a 5.54 a
x x x x
362.9 g 454.0 g
5.Ob 6.1d 7.3b
25.0 86.2 a ..97.5a
38 a 5.20 ab
* Means separation within columns by Duncan's multiple range
test, 5% level.