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Do not assume content reflects current
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PROCEEDINGS
of the
35th Southern Pasture and Forage Crop
Improvement Conference
June 13-14, 1978
Sarasota, Florida
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Science and Education Administration
U.S. Department of Agriculture
PROCEEDINGS
OF THE
35TH SOUTHERN PASTURE AND FORAGE CROP
IMPROVEMENT CONFERENCE
June 13-14, 1978
Sarasota, Florida
Sponsored by
the Agricultural Experiment Stations
of
Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi,
North Carolina, Oklahoma, Puerto Rico, South Carolina,
Tennessee, Texas, and Virginia
and the
Science and Education Administration
U.S. Department of Agriculture
Published by the Office of the Regional Administrator for Federal Research
(Southern Region), Science and Education Administration, U.S. Department of
Agriculture, New Orleans, La. 70153, from camera-ready copy supplied by the
authors, who accept responsibility for any errors in their papers. The opinions
expressed by the authors are not necessarily those of the U.S. Department of
Agriculture. Mention of pesticides does not constitute a recommendation for
use by USDA, nor does it imply that the pesticides are registered under the
Federal Insecticide, Fungicide, and Rodenticide Act as amended. The use of
trade names does not constitute a guarantee, warranty, or endorsement of the
products by USDA.
This publication is available from Homer D. Wells, Science and Education
Administration, Tifton, Ga. 31794.
Issued September 1978.
ii
CONTENTS
Page
Plant Communities of Peninsular Florida
James A. Wolfe 1
Improved Forages
O. Charles Ruelke 5
Florida's Range Resource: A Primary Source of Forage
R. S. Kalmhacher 10
The Florida Dairy Industry
Barney Harris, Jr 19
Forage Grass Breeding at the University of Florida
K. H. Quesenberry 21
Selection and Breeding of Legumes in Florida
Albert E. Kretschmer, Jr 23
Grazing Management Research With Improved Forages at Gainesville
W. R. Ocumpaugh 24
Forage Research at Ona
P. Mislevy 26
Forage Quality Evaluation at the University of Florida
John E. Moore 30
N2~Fixation Research With Tropical Grasses
K. H. Quesenberry , R. L. Smith, and S. C. Schank 33
Systems for Making, Handling, Storing and Feeding Large Hay
Packages
B. L. Bledsoe 35
Evaluating Forage Characteristics Using a Dynamic Model of
Fiber Disappearance in the Ruminant
D. R. Mertens and L. O. Ely 49
Cattle Cycles — Research Response
Marvin E. Riewe 65
Grazing Subtropical Pastures — Components and Systems
Elver M. Hodges 72
Looking to the Future in Forage-Animal Production
R. E. Blaser 75
iii
Page
Breeding and Selecting Legumes for Greater N2~Fixation as Seen by
a Microbiologist
Harold L. Peterson ...... 85
Panel Discussion: Breeding Grasses and Legumes for Use in Mixtures
Introduction: Complexity and Challenges
Pryce B. Gibson 96
Summary of Ecological Considerations in Relation to the Breeding
and Development of Legume Cultivars Which Can Be Grown in Grass-
Legume Mixtures
O. Charles Ruelke . . 98
Importance of Mixed Stand Evaluation in Breeding and Variety
Development — Annual Legumes
(V. E. Knight 100
Breeding Annual Grasses for Use in Grass-Legume Mixtures
C. E. Watson, Jr 104
Perennial Legumes
W . A . Cope 108
Breeding Perennial Grasses for Grass-Legume Mixtures
R. L. Haaland and C. S. Hoveland 113
Breeding Forages for Use in Mixtures West of the Mississippi
Ethan C . Holt 115
Sclerotinia Crown and Stem Rot of Alfalfa in North Carolina
Ronald E. Welty and Thad H. Busbice 118
Breeding for Pest Resistance in Red Clover
N. L. Taylor and R. R. Smith 125
Enzyme-Linked Immunosorbent Assay (ELISA) for Detection
and Identification of Forage Legume Viruses
M. R. McLaughlin and O. W. Barnett 138
Collection of Clover Species in Greece, Crete, and Italy
R. R. Smith, N. L. Taylor, and W . R. Langford 146
Recent Developments in Breeding and Selection of Tropical Legumes
( Stylosanthes ) for the Deep South
J. B. Brolmann 156
Contributors 158
IV
PLANT COMMUNITIES OF PENINSULAR FLORIDA
By James A. Wolfe
In spite of its relatively youthful geologic age, peninsular Florida has
a diverse and distinctive flora. A subtropical climate is favorable for the
survival of many kinds of native and exotic plants. Subtropical or peninsular
Florida is the part of the state from the Gainesville vicinity southward. It
roughly corresponds to the hyperthermic region as used in soil taxonomy (1_, 3_) .
While climate has been a dominant factor in determining the rich flora of
Florida, the influence of soils has also been great. With few exceptions, the
parent material for soils of peninsular Florida is marine deposits of Pleisto-
cene age. The landscape is characterized by a series of former shoreline
ridges and marine terraces that were formed during interglacial periods when
the sea level was higher than at present. The highest areas, being the first
to emerge from the sea, have undergone more alteration than the lower, nearly
level terraces or flatwoods. The older Central Highlands, no longer resembling
a terrace, have karst topography characterized by numerous lakes and depres-
sions resulting from the collapse of solution caverns in the underlying lime-
stone. Recent or Holocene surfaces are conspicuous along the seashore and
major streams and in marshes and swamps where organic matter has accumulated.
Recent geologic deposits are most apparent in coastal areas where changes
occur to varying degrees with each wave, tide, or tropical storm. Under the
stabilizing influence of plants adapted to these areas, marine sediments accu-
mulate and land is formed. The nature of the resulting soils is closely re-
lated to the kinds of deposits. Sands and broken shells accumulate in beaches
and adjacent barrier dunes producing sandy soils. In the shelter of lagoons
and tidal inlets, finer sediments accumulate.
Vegetation in coastal areas shows zonation with different stages of pri-
mary succession related to progressively older deposits. On barrier dunes,
conspicuous plants are sea-oats (Uniola paniculata) , beach morning-glory ( Ipo-
moea pes-caprae) , and bitter panicum (Panicum amarum) . Saw palmettos ( Serenoa
repens) become established shortly after the rhizomatous pioneer plants stabi-
lize the shifting sands. Live oaks (Quercus virginiana) and other species of
trees and shrubs eventually become established and create dense thickets. The
climax plant community is a hardwood hammock with many epiphytes attached to
the branches of spreading live oaks.
Mangrove swamps are very important as spawning and feeding grounds for
fish and shellfish, but they also play an important role in land formation.
Red mangroves (Rhizophora mangle) , which have prop roots extending out into the
water, are the pioneer plants. As sediments accumulate and land builds up,
succession proceeds through stages of black mangroves (Avicennia nitida) ,
white mangroves (Laguncularia racemosa) , and eventually other plants. The
southern tip of the peninsula has extensive mangrove swamps. Toward the north
they are eliminated by freezing and are replaced by tidal marshes where the
vegetation is mainly smooth cordgrass ( Spartina al ternif lora) , marshhay cord-
1
grass (S. patens) , black needlerush (Juncus roemerianus) , and seashore salt-
grass (Distichlis spicata) .
In the interior of the peninsula, the wetlands, flatwoods, and sand
ridges have distinctive types of vegetation. The wetlands have very poorly
drained soils that are commonly organic (muck) or mineral soils with a high
organic matter content. The flatwoods have poorly drained, sandy soils. The
water table is near the surface during the summer rainy season, but during
prolonged periods of low rainfall these soils become extremely dry. Soils of
the flatwoods are characteristically Spodosols--formerly called ground-water
Podzols--except in areas with shallow, porous limestones in the extreme south-
ern tip of the peninsula. The sand ridges have freely drained soils and are
of two types. Karst ridges are on the Central Highlands, and former shoreline
ridges run almost parallel to the ocean along the lower marine terraces.
The wetlands are swamps dominated by woody plants and marshes dominated
by grasses and grasslike plants. Cypress swamps, deciduous hardwood swamps,
and evergreen hardwood swamps (bay swamps) are widely distributed along
streams and in depressions. The most extensive marshes are in the Everglades
region, but they are common along streams and in ponds in other parts of the
state. Many of the marshes are dominated by sawgrass (Cladium jamaicense),
pickerelweed (Pontederia cordata) , or other herbaceous hydrophytes. Some
marshes are dominated by maidencane (Panicum hemitomon) , an excellent forage
species .
Other grasslands with poorly drained soils occur in areas that are cover-
ed by water for a shorter time than the very poorly drained marshes. This
type of wet grassland sometimes surrounds marshes but is more common along
major drainage systems and in sloughs in flatwoods areas. Wet grasslands are
more extensive toward the tip of the peninsula. Broad areas of nearly tree-
less wet prairie are in the vicinity of Lake Okeechobee and the Everglades,
and smaller areas are along the St. Johns River. Many of these areas are arti-
ficially drained, but before they were drained a sheet of water covered the
ground for 2 to 7 months after the summer rainy season began. These grass-
lands are naturally adapted to grazing, and in many areas they have been con-
verted to improved pasture. Blue maidencane (Amphicarpum muhlenbergianum) and
chalky bluestem (Andropogon capillipes) are important native forage grasses.
With prolonged heavy grazing, however, sand cordgrass (Spartina bakeri), wire-
grass (Aristida str icta) , and broomsedge bluestem (Andropogon virginicus)
often increase and become dominant.
The flatwoods are broad, nearly level marine terraces. These pine-pal-
metto communities are the most extensive of the natural communities of central
and southern Florida. The landscape is an open forest of slash pine (Pinus
elliottii) with longleaf pine (_P. palustris) and pond pine (P. serotina) being
numerous in some localities. The understory is commonly a dense growth of
saw palmettos. Many flatwoods areas are used as native range. Wiregrass com-
monly is the most abundant grass; however, in areas that are not overgrazed,
more palatable grasses such as chalky bluestem, creeping bluestem (A. stoloni-
fer) , and lopsided indiangrass (Sorghastrum secundum) are important forage
species. These areas are frequently chopped or burned to control saw palmettos
and other undesirable plants that compete with the more desirable grasses.
This community has a long history of natural and man made fires. It is con-
sidered to be a fire subclimax community. If fire or other disturbances were
eliminated for a very long time, these areas would eventually develop other
types of communities.
2
The sand ridges have freely drained soils. The water table is ordinarily
below a depth of 20 inches and in most areas it is much deeper. The two most
widespread types of vegetation are the sand pine scrub (sand pine - scrub oaks)
and the longleaf pine - turkey oak communities. Both communities are fire sub-
climaxes. Without periodic burning, they would develop into some type of ham-
mock. The sand pine scrub type occupies the most infertile areas of the sand
ridges. In addition to sand pine (Pinus clausa) , this community is character-
ized by scrub oaks: myrtle oak (Quercus myrtifolia) , sand live oak ((^. vir-
giniana var. geminata) , and Chapman oak ((£. chapmanii) . The soils are highly
leached and very droughty, and white sand shows through the sparse groundcover
in many areas. Sand pine scrub communities are common on relict dunes of
former shoreline ridges and in the driest areas of the Central Highlands, espe-
cially in the Ocala National Forest. Longleaf pine - turkey oak communities
are widely distributed in the Central Highlands. Agriculturally developed
areas are in improved pasture and citrus. Where natural vegetation remains,
the landscape is an open forest characterized by longleaf pine, turkey oak
(^. laevis) , and some bluejack oak (Q. incana) . Saw palmettos are scattered
and the ground cover is commonly wiregrass. While soils are not so highly
leached as those of the sand pine scrub, they are naturally infertile and
droughty.
Several types of hammock are in Florida. A hammock is a type of plant
community dominated by broadleaf evergreens, for example, large, spreading
live oaks. Some hammocks are climax communities and some are preclimaxes.
The total acreage for hammock communities is small due to fire or other dis-
turbances. Without disturbance, most areas, except those with very poorly
drained soils, would apparently develop some type of hammock. Tropical ham-
mocks characterized by gumbo-limbo (Bursera simarouba), strangler fig (Ficus
aurea) , poisontree (Metopium toxiferum) , Jamaica dogwood (Piscidia communis),
marlberry (Ardisia escallonioides) , and other tropical species are in the ex-
treme southern part of the state. Other hammocks occupy hydric, xeric, or
mesic sites throughout the rest of the peninsula. The hydric or wet hammocks
are common along streams and sloughs. They have an abundance of cabbage palm
(Sabal palmetto) as well as live oak and laurel oak (Q. laurifolia) . Xeric or
dry hammocks are on the sand ridges and are the result of exclusion of fire
from longleaf pine - turkey oak and sand pine scrub communities. Two indi-
cator species of the mesic hammock are southern magnolia (Magnolia grandif lora)
and American holly ( Ilex opaca) , and the mesic hammock is sometimes called the
Magnolia-Ilex climax (_2) . Large spreading live oaks and other large trees are
also present. The mesic hammock is considered to be the climatic climax com-
munity for central Florida. It is the final stage in succession and its acre-
age is comparatively small because of many past disturbances. Mesic hammocks
occur on many freely drained soils, but succession is more rapid in soils with
favorable moisture conditions. Hammocks have little value for forage but can
provide shelter for livestock and wildlife. Because of their attractive
setting, they are desired for community development.
LITERATURE CITED
1. Brasfield, J. F. , and V. W. Carlisle. 1975. Soil temperatures of North
Florida. Soil and Crop Sci. Soc. FI. Proc. 35: 170-173.
2. Shelford, V. E. 1963. The ecology of North America. Univ. Illinois
Press, Urbana.
3
3. Soil Survey Staff. 1975. Soil taxonomy — - A basic system of soil class-
ification for making and interpreting soil surveys. U. S. Dept. Agric.
Handbook No. 436.
4
IMPROVED FORAGES
By 0. Charles Ruelke
Improved forages have been a key factor in the initial survival and later
development of improved livestock in Florida. Without improved forage species
and forage management systems it would be impossible to support improved breeds
of livestock, especially high producing dairy cows, unless a major proportion
of the feed requirement is shipped in to Florida. In some countries, like the
British Isles and New Zealand, most if not all of the feed requirements come
from improved forages. Florida has favorable climate, available land and many
improved forage species to choose from to meet the animal feed requirements.
Our task as research workers is to find the best species adapted to particular
sites, and manage them in such a way as to provide the feed requirements at a
minimum cost.
The environment of Florida is extremely variable with a temperate
climate in northwest Florida to a sub-tropical climate in south Florida, and
tropical storms to extreme dry conditions. Some of the most fertile organic
muck soils are found in Florida, as well as some of the most sterile sand dunes
which occur along Florida's coasts. Florida is a world source of phosphate
fertilizer deposits as well as completely sterile sand that can be used direct-
ly from the field to do nutrient deficiency research.
Likewise, Florida's forage species range from the poorest, unpalatable,
indigestible native species like sedges and rushes to the most productive, pal-
atable and digestible species known, like white clover and ryegrass. Acreages
of improved forages are shown in Table 1. The seasonal distribution of forage
species throughout north, central and south Florida is shown in the grazing
calendar, Figure 1. This grazing calendar includes only a few of the many pos-
sible forage species which can be grown in Florida. Herein is one of the prob-
lems, or opportunities, depending upon how you look at it. With so many dif-
feren species to choose from, it is difficult to develop breeding and manage-
ment research on all of the species which have potential for forage. Likewise,
with so many different species to choose from it is possible to select a culti-
var for a particular ecological niche.
In Florida, several different procedures for obtaining improved forages
have been very successful. 'Pensacola' bahiagrass, an improved bahiagrass
cultivar, was selected from bahiagrass plants which were found along the docks
near Pensacola, Florida, where bananas, which were packed in hay, were unloaded.
Today, bahiagrass is the most extensively grown improved grass in Florida.
'Pangola' digitgrass, which was introduced from the region of the Pongola
river in South Africa, is now one of the most extensively grown grasses in cen-
tral and south Florida. This important improved grass is believed to have ori-
ginated as a natural hybrid in Africa. Its forage potential was not realized
there, but thanks to the keen eye and imagination of several Florida scientists,
it has been vegetatively propagated and grown in Florida and distributed
throughout sub-tropical and tropical regions all over the world. It is inter-
esting to note that all of the 'Pangola' cultivar of digitgrass that exists in
5
Table 1. --Acreages of grasslands in Florida*
1 terns
197*4
acres
Projected
1980
ac res
Acreages
1985
acres
Total Grassland
12,167,000
1 1 ,967,000
1 1 ,767,000
Range pastures
3,969,000
3,738,000
3,383,000
Woodland pastures
*+,698,000
*+,600,000
3,500,000
Improved permanent grass pastures
3,125,000
3,220,000
3, *+37, 000
D i g i tg rasses
628,000
6*+8 ,000
691 ,000
Bah i ag rasses
2 ,2*45 ,000
2,312,000
2, *+69, 000
Bermudag rasses
186,000
192,000
20*+, 000
M i seel 1 aneous
66,000
68,000
73,000
G rass- 1 egume
(*+ *+7,000)
(500,000)
(600,000)
Tempora ry^
688,000
801 ,000
955,000
Summer annuals
221 ,000
2 *+ 5 ,000
280,000
Millet
65,000
75,000
90,000
Sorghum X sudan
36,000
*+5 ,000
60 ,000
Alyce Clover
50,000
60,000
70,000
Indigo
50,000
50,000
50,000
M i seel 1 aneous
20,000
25,000
30,000
Winter Annuals
*+67,000
5*46 ,000
655,000
Rye
101 ,000
10*+,000
1 1 1 ,000
Wheat
12,000
13,000
1 *t , 000
Oats
28,000
29 ,000
30,000
Ryeg rass
326,000
*+00,000
500 ,000
S i 1 age
23 ,000
29,000
*+2,000
Corn
16,000
20,000
30,000
Sorghum
7,000
9,000
12,000
Hay ^
(188,000)
(207,000)
(226,000)
Most of these acreages included in improved permanent grass pastures;
overseeded with winter growing legumes or harvested for hay.
2
About 50 percent of temporary pasture acreage is double cropped.
*Data prepared for commodity report of the Forage, Range and Pasture
Committee presented to Agricultural Growth in an Urban Age Conference,
Feb. 11, 1975-
From: Ruelke, 0. C. and G. B. Killinger, 1977- Chapter 11. Forage and
Pastures from Beef Cattle in Florida Bull 28: Fla. Dept, of Ag r i c . and Consumer
Service and Inst, of Food & Agric. Sci. pp 1*+3_16*+.
6
Figure 1. — Grazing Calendar for Florida
GRAZING CALENDAR
WINTER | SPRING
JAN-MAR APR-JUIM
SUMMER, FALL
JUL-SEPT OCT-DEC
NORTH FLORIDA
From: Ruelke, 0. C. and G. B. Killinger 1977.
Beef Cattle in Florida. Bui. 28. Fla. Dept, of
Agriculture and Consumer Services and Institute of
Food and Agricultural Sciences. Ch. 11. pp IA3-I6A.
7
pastures throughout the world originated from a clone evaluated in the plant
introduction nursery of the Florida Experimental Station at Gainesville,
Florida, and recent plant explorations into Africa have not been able to find
the genetically identical plant in existence in the region where it was origin-
ally found .
Bermudag rasses are also extremely important as improved forages for Flor-
ida and all of us here are familiar with the outstanding work of Dr. Glen
Burton and the breeding of 'Coastal', 'Coastcross 1', and more recently 'Tifton
kk' bermudag rass . More recent introductions from Africa and Europe, and incor-
poration of these in breeding for higher production, higher digestibility, and
better adaptation to eliminate stress of cold and drought, have resulted in far
superior cultivars of bermudagrass for Florida and all of the world.
Many other introduced and improved genera of grasses have contributed to
the improved forage supply of specific areas of Florida. These include grasses
of the genera Axonopus, Brachiaria, Cenchrus, Ch 1 or i s«,Ech i neco 1 oa , Hemarthria,
Lol i urn, Pan i cum , Paspal urn, Pennisetum, Secale and Stenotaphrum .
Legumes have also played a very important role in the forage program in
Florida. It has been demonstrated that you cannot grow white clover success-
fully in Florida, and also that you can grow white clover successfully in Flor-
ida. Choice of site and management research brought out the keys to success.
In early work on sites favorable for grazing white clover, with proper manage-
ment, average weaning percentages increased from 63%, on fertilized grass pas-
tures, to 8l% on grass clover pasture with no nitrogen applied. In central
Florida, early work, Table 2, has shown higher calf weaning percentage, calf
weaning weights, slaughter grades and calf production per cow and per acre from
improved grass clover pastures than from native or native and improved grass
pas tu re .
In south Florida, because of its subtropical wet climate, there has been
an excellent opportunity to evaluate many of the tropical legumes, as well as
to breed improved cultivars. This work has led to the use of many new genera
of legumes including Aeschynomene , A 1 ys i carpus , Arach i s , Caj anus , Cent rosema ,
Cl i tor i a , Desmod i urn , G 1 yc i ne , I nd i gofera , Leucaena , Lab 1 ab , Macropt i 1 u im,
Puerar i a , V i gna and Zorn i a .
Finally, no improved forage program would be complete without research on
preservation of forage as hay, haylage, dehydrated forage, pellets and silage.
Cooperative research between agronomists, animal scientists, dairy scientists,
and animal nutritionists have made it possible to devise systems for handling
and evaluating improved forages and determining the economic returns.
In closing may I take this opportunity to welcome you to our state. We
hope your visit here will stimulate and exchange new ideas regarding the use of
improved forages.
8
Table 2. --Average production, supplemental feed,
pasture treatement per cow season over a five-year
period grazing native, native plus improved and
all improved grasses and clover pastures *
Comb i nat i on
A 1 1 Improved
Native S
with 1 r r i gated
Pasture System
Native
Improved
C 1 over
Number of acres
772
388
107
Production Data
(73 Improved)
(27 1 rr i gated)
No. cow seasons
303
295
300
Av . wt. cows (lb.)
889
942
1017
Cal f wean i ng %
63
75
81
Calf weaning wtj (lb.)
Slaughter grade
380
457
504
9
10
1 1
Calf production/cow (lb.)
241
340
406
Calf production/acre (lb.)
19
52
228
Supplemental feed cow (lb)
Hay
555
43
280
Cottonseed meal
52
65
-
Citrus meal
52
31
-
Common salt
35
34
-
M i nera 1
39
37
17
Pasture Treatment
Fer t i 1 i zer/cow (lb.)
Complete fertilizer
-
237
500
Ammon i urn nitrate
-
102
133
0-8-24
-
169
133
Muriate
-
-
25
L i me
-
339
500
Renovation (acres)
-
0.
34
0.32
Hubam seed (lb.)
-
5
-
Electrici ty KWH
217
' Grades: 9 ~ Low Good;
10
- Good ; 1 1
- High Good
“Peacock, F. M., E. M.
Hodges, W. G.
Kirk, and M .
Koge r
1967. Cow-Calf
Program on Native, Improved
and
a Combination of Native
and
Improved Pastures.
Beef Cattle Short Course, University of Florida, Gainesville, Florida.
9
FLORIDA'S RANGE RESOURCE: A PRIMARY SOURCE OF FORAGE
By R. S. Kalmbacher
Florida's native-forage pastures cover 3.85 million hectares (1_)
(including grazable woodland) which is seven times greater than the land area
of the state of Delaware. In terms of value for wildlife habitat, water re-
charge and esthetics this represents an important resource, but consideration
to the production of indigenous forages which historically has been supporting
cattle for more than 400 years makes native range an integral part of
Florida's livestock industry.
When people think of rangeland, they most often relate to the western
areas, unaware of Florida's resource. Unlike the rangelands west of the 100th
meridian, Florida has abundant rainfall which permits greater annual forage
production. Short and tall grass prairie rangelands of the western U.S. receive
annual rainfall of 25 to 100 cm but in Florida rainfall frequently exceeds 140
cm annually.
Much of Florida's productive rangeland is on the central and southern
peninsula. The soils, with the exception of peats and mucks, are sandy and low
in fertility. Even though they respond to fertilization (16), rangelands do
not receive lime or fertilizer.
Approximately 332 native grasses occur in Florida (23) , but only 10 to 15
produce most of the forage consumed by cattle. These grasses of economic
importance are characteristic of the site where they grow. A "site" is a
natural plant community adapted to rather broad - but distinctive - environ-
mental conditions. Some of the major sites and their important grass species
are listed in table 1. Because the flatwood site is the largest type, it has
received the greatest amount of research attention in the past 20 years. The
discussion of Florida's range management that follows will deal almost
exclusively with flatwoods grass species. The purpose of this paper is to
familiarize you with Florida range through a review of the literature since
the 1940' s.
A major tool used in range management has been fire or prescribed burning.
Flatwoods are generally burned every two or three years to remove that hazard
of accumulated fuel and to improve forage quality. After a burn pineland
threeawn (Aristida stricta) , also referred to as "wiregrass", regenerates
rapidly. In a south Florida study by Hilmon and Lewis (4) this grass comprised
957c of the total herbage three weeks after a February burn. Pineland threeawn
yields at three weeks after burning equaled 74 kg of dry matter/ha but
increased to 3360 kg/ha after one and one-half years. Research at the R ange
Cattle Station at Ona , Florida (2^) indicated that crude protein in pineland
threeawn varied from 107> shortly after burning to 1% to 2% percent in mature
forage. Other researchers have observed a similar drop in forage quality
(3, 5, 6, 7, 9, 10, 1J., 12, 14, L5) which is associated with a decline in this
species' consumption by cattle four to six months after burning. After pine-
land threeawn maturity, cattle prefer the more palatable tall grasses viz.
bluestems, indiangrass and Paspalums ((3) . Generations of Florida cattlemen
10
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Adapted from Important Native Grasses for Range Conservation in Florida. USDA.
Gainesville, Florida.
have managed rangeland by the philosophy of burn and graze. This led Yarlett
(22) to conclude that repeated burning and uncontrolled grazing led to a
decrease in the tall grasses.
Prior to 1960 the research effort had been devoted to native range as a
producer of pineland threeawn. There was nothing in the literature about
Florida's native tall grasses. Certainly, ranchers were aware of their exis-
tence but not their importance. This recognition came about through a few key
people, primarily within the USDA - Soil Conservation Service and Forest
Service. Yarlett (23) described some important flatwoods grasses: creeping
bluestem (Schizachyrium stolonifer) , chalky bluestem (Andropogon capillipes) ,
toothachegrass (Ctenium aroma ticum and C. floridanum) , lopsided indiangrass
(Sorghastrum secundum) and blue maidencane (Amphicarpum muhlenbergianum) .
Later Yarlett (23) compiled data from field observations on many of the
important range grasses and described the distribution, site adaption and
superficial habits of growth, development, and reactions to grazing. In a
more detailed work conducted at the SCS plant materials center in south
Florida Yarlett and Roush (25) described the above characteristics of creeping
bluestem emphasizing its potential. Roush and Yarlett (20) were less descrip-
tive and leaned more toward management when they compared creeping bluestem
with chalky bluestem, south Florida bluestem (Andropogon rhizoma tus) broom-
sedge (A. virginicus) , and Florida threeawn (Aristida rhizomorophora) and
found that creeping bluestem out-yielded the other four grasses. The yields
of three of the more desirable range grasses are compared with pineland three-
awn in table 2. Unfortunately there has been little consistency or qualifica-
tion in expressing the yields of the native grasses. Many of the yields
reported do not accurately reflect the herbage of value to livestock. An
example is that yields often represent forage accumulated after several years
growth .
Higher yields resulting from a change in the botanical composition due
to chopping with tendem-drum type choppers and resting flatwoods range have
been reported (16 , 18, 24). It seems that overgrazing flatwoods range had
eliminated the more desirable tall grasses except under the saw palmettos
(Serenoa repens) where cattle could not graze them. Chopping and resting for
one to two years allows the more desirable grasses to increase. Lewis (16)
noted that dry matter yield on chopped, unfertilized range increased from
900 kg/ha to 2420 kg/ha two to five years following treatment. Moore (18)
noted a desirable increase in Andropogons , Panicums and Paspalums and a marked
decrease in Aristida species. Two years after chopping, dry matter production
was 6050 kg/ha. Yarlett (24_) indicated that green weight yields of creeping
bluestem increased from 1790 to 6730 kg/ha at three and eleven months after
chopping, respectively. Yarlett and Roush (25) stated that creeping bluestem
increased from about 200 kg/ha to 4260 kg/ha of air-dried material per hectare
1 year after chopping. In grazeable woodlands these yields increased 170 to
2240 kg/ha.
Forage quality from Florida's native range generally reflects the low
fertility of the native soil. Table 3 contains a summary of some quality para-
meters reported for various grasses. Most of the work has been done on
pineland threeawn. Some data are available from fairly recent quality
estimates such as Ln vitro or Van Soest analyses.
12
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14
Analysis includes other blues tem grasses.
Grazing Management and Animal Response
It has been considered that approximately 6 hectares of native range is
necessary to support a single cow weighing 290 to 410 kg. Kirk et a_l . (13)
found that unsupplemented cow/calf herds grazing unburned pineland threeawn
range had a 61% calf crop and calf production was 19.8 kg/ha when stocked at
one cow per 8.1 ha. When stocked at 1 cow per 6.4 ha on range where one half
the experimental area had been burned and cattle received molasses for a 135
day period, calf crops were 72% with calf production at 23.3 kg/ha. The mean
205-day calf weights on these two treatments were 172 and 176 kg, respectively.
Hughes (7) reported pineland threeawn utilization at 63%, 52% and 46% with
stocking rates of one cow per 6.1 ha, 8.9 ha, and 14.6 ha, respectively,
seven months after burning.
The most common and practical method of management is to combine native
and improved pastures to provide the best utilization of native forage and
maintain the breeding herd in good productive condition. When using the
premise of one cow/6 ha, Jones e_t a_l. (8) at the Range Cattle Station at Ona
replaced 3 to 4 ha of native range with 0.4 ha of improved pasture. Cattle
had access to native range and rotationally grazed pastures with no supple-
mental feed. During this five year study cows of breeding age averaged an 80%
calf crop and 193 kg weaning weight.
During a 5-year study at Ona ARC to compare cow-calf production from
native, combination of native and improved, and improved pastures Peacock e_t a_l
(19) reported birth and weaning rates on the native pasture were 65% and 6370,
respectively, compared to 78% and 75% for the combination and 83% and 81% for
the improved system (table 4). Average 205-day weights were 173 kg, 196 kg
and 208 kg, respectively with market grade values of 8.7, 9.7 and 10.9 listed
in order of increasing intensification. These differences demonstrated the
annual distribution of forage quantity and quality.
A system frequently used today which may optimize the annual distribution
of forage quality and quantity of native and improved pastures is to place cows
on native pastures after weaning in the fall. Calves are born on the range
supplemented with mineral and protein, then cows and calves are moved to
freshly fertilized, improved pasture for the spring and summer. Such a system
is intuitive: there is no research to support it as the most nutritionally or
economically expedient in terms of livestock production.
Economics
Adequate data on costs and cattle production are not available to make an
accurate economic evaluation of native pastures. One point can be stressed in
an economic discussion about Florida's native range, and that is, that the
resource does have the potential of off-setting some of the cash costs of calf
production. Management costs on a per hectare basis are lower than those of
improved pastures.
Summary
The native range represents a valuable resource for Florida cattlemen.
Native pastures prior to 1960 were managed for pineland threeawn, but emphasis
has shifted to management for the more palatable, higher producing bluestems,
maidencane, indiangrass, etc. Research underway within Florida's Institute of
Food and Agricultural Sciences (IFAS) involves measurement of the plant
15
TABLE A. --Adjusted means for birth, weaning, weaning weight, 205-day
weight, market grade and age at weaning of calves from cows
on three south-Florida pasture systems. Ona , Agricultural
Research Center. 1962-1966^
Pasture System
Na tive
Native & Improved
Improved
Birth rate %
65
78
83
Wean rate %
63
75
81
Weaning weight kg
173
207
229
205-day weight kg
173
196
208
Market graded
8.7
9.7
10.9
Wean age (days)
209
220
229
i
+
From Peacock e_t al. (19)
8, high standard; 9, low good; 10, good, 11, high good.
16
response to grazing, saw palmetto control, effect of fire and grazing on the
important tall grasses, range rehabilitation, and chemical composition of
the more desirable native grasses.
LITERATURE CITED
1. Anonymous. 1970. Conservation needs inventory. USDA. SCS., Gainesville,
Florida .
2. Davis, G. E. and W. G. Kirk. 1952. Nutritional quality in pastures.
Soil Sci. Soc. Fla. 12:106-110.
3. Halls, L. K. , 0. M. Hale, and B. L. Southwell. 1956. Grazing capacity
of wiregrass-pine ranges of Georgia. Ga . Agr. Exp. Sta. Tech. Bull.
NS2 38pp.
4. Hilmon, J. B., and C. E. Lewis. 1962. Effect of burning south Florida
range. USDA. Forest Service Station paper No. 146.
5. Hilmon, J. B., and R. H. Hughes. 1965. Fire and forage in the wiregrass
type. J. Range Mgt. 18:251-254.
6. Hughes, R. H. 1970. Cattle grazing management on pine-wiregrass type.
J. Range Mgt. 23:71-72.
7. Hughes, R. H. 1974. Management and utilization of pineland threeawn
range in south Florida. J. Range Mgt. 27:186-192.
8. Jones, D. W. , E. M. Hodges, and G. W. Kirk. 1960. Year-round grazing
on a combination of native and improved pasture. Florida Agr. Exp. Sta.
Bull. 554 A 14pp.
9. Killinger, G. B. 1948. Effect of burning and fertilization of wiregrass
on pasture establishment. J. Amer. Soc. Agron. 40:381-384.
10. Kirk, W. G. , A. L. Shealy, and B. Knapp, Jr. 1945. Weight changes of
cattle on a Florida range. Fla. Agr. Exp. Sta. Bull. 418.
11. Kirk, W. G. and G. K. Davis. 1970. Determination of blood components
of cows on native range: inorganic P and Ca ; hemaglobin and hematocrit.
J. Range Mgt. 23:239-253.
12. Kirk, W. G. and E. M. Hodges. 1970. Effect of controlled burning on
production of cows on native range. Proc. Soil and Crop Sci. of Fla.
30-341-343.
13. Kirk, W. G. , E. M. Hodges, F. M. Peacock, L. L. Yarlett, and F. G. Martin.
1974. Production of cow-calf herds: effect of burning native range and
supplemental feeding. J. Range Mgt. 27:136-139.
17
14. Kirk, W. G. , G. K. Davis, F. G. Martin, E. M. Hodges, and J. F. Easley.
1974. Effect of burning and mowing on the composition of pineland
threeawn. J. Range Mgt. 27:420-423.
15. Kirk, W. G. , G. K. Davis, F. G. Martin, E. M. Hodges and J. F. Easley.
1975. Pineland variety grass provided much forage. Florida Cattleman.
July, 1975.
16. Lewis, C. E. 1970. Response to chopping and phosphate on south Florida
range. J. Range Mgt. 23:276-282.
17. Lewis, C. E., R. S. Lowrey, W. G. Monson and F. E. Knox. 1975. Seasonal
trends in nutrients and cattle digestibility of forage on pine-wiregrass
range. J. An. Sci. 75 (II) 208-212.
18. Moore, W. H. 1974. Some effects of chopping saw palmetto-pineland
threeawn range in south Florida. J. Range Mgt. 27:101-104.
19. Peacock, F. M. , M. Koger, W. G. Kirk. E. M. Hodges, and J. R. Crockett.
1976. Beef production of Brahman, Shorthorn, and their crosses on
different pasture programs. Fla. Agr. Exp. Sta. Tech. Bull. 780. 19pp.
20. Roush, R. D. , and L. L. Yarlett. 1973. Creeping bluestem compared with
four other native range grasses. J. Range Mgt. 26:19-21.
21. Wichman, F. F. , and R. E. Fox. 1950. Analyses of grazing plants in
the western Gulf region. USDA.-SCS. Ft. Worth, Texas.
22. Yarlett, L. L. 1963. Some important and associated native grasses on
central and south Florida ranges. J. Range Mgt. 16:25-27.
23. Yarlett, L. L. 1965. Important native grasses for range conservation
in Florida. USDA, SCS., Gainesville, Florida.
24. Yarlett, L. L. 1965. Control of saw palmetto and recovery of native grasses.
J. Range Mgt. 18:344-345.
25. Yarlett, L. L. and R. D. Roush. 1970. Creeping bluestem (Andropogon
stolonifer) . J. Range Mgt. 23:117-122.
18
THE FLORIDA DAIRY INDUSTRY
By Barney Harris, Jr.
The dairy industry in Florida is geared to meet state needs for fluid
milk, providing approximately 94% of the fluid milk consumed. Milk produc-
tion in Florida has been increasing at a steady rate since the end of World
War II, with notable gains since 1965. Increased production is the result of
a steady increase in dairy cow numbers as well as in milk yield per cow.
Since 1965, the number of dairy cows in Florida has increased an average of
2% to 3 °/ per year, while the US dairy cow population has been decreasing.
In 1977, Florida had the largest average dairy herd size in the U.S.A.,
with 400 dairies having an average of 500 cows. Another distinguising
characteristic of Florida dairies is their heavy use of use of commercial
feeds: Florida dairymen use a higher proportion of commerical feeds than
milk producers in any other state. However, through the use of by-product
feedstuffs such as molasses, citrus pulp, and fiber feeds such as cottonseed
hulls and sugarcane bagasse pellets, the proportion of concentrates, such
as corn and wheat are usually below the average for other dairy states.
In penisular Florida, a large majority of the dairies use complete
feeds containing cottonseed hulls or sugarcane bagasse pellets. In the
northwest or panhandle area of the state, the feedstuffs includ corn silages,
hay crop silage and excellent winter pastures. The variation in feedstuffs
used is principally due to her size, land fertility, labor problems and land
avai 1 ai 1 i ty and costs .
Dairymen have shown a greater interest in growing corn silage in recent
months. The increased interest has developed primarily as a result of the
large fluctuation in the cost of by-product roughages and the desire to use a
good roughage. In many cases, a double and triple cropping system is being
used to grow forages.
Also, a few Florida dairymen have extended their silage feeding program
from a few months of feeding to year round feeding of silage. Year round
feeding of silage has certain advantages in that it provides the dairymen with
more ease in maintaining a normal milk fat test, a more consistent feeding
program, and a source of roughage during the summer months when roughages are
frequently expensive. Because of the environmental conditions in Florida,
dairymen find that high producing coes can consume up to about 50 lbs of silage
during the cool months and 30 lbs during the summer months. Lower producing
cows can consume more silage since less grain is needed to meet their energy
requi rements .
Storage facilities for bulk feeds are available at most dairies. In
general, a number of 25 to 30 ton storage tanks are installed at the larger
19
dairies to handle either a complete feed or certain ingredients plus a pre-
mix. Storage facilities for silage in general include upright silos for
smaller dairies and bunker or tranch silos for larger dairies.
The feed handling equipment that appears to be the most popular in new
dairies for feeding cows is the mixer wagon with scales and the timing
system (similar to the Badger feeder). Both systems will deliver measured
amounts of feed to dairy cows so that the manager can keep a running account
on the amount of feed being consumed. Each system is common in Florida and
can be observed at a number of dairies
The feeding area commonly used in the larger dairies includes a milking
palor, a feed barn and a bunk for feeding on the outside. The feed barns are
paved and, in most cases, contain individual stanchions. Most new barns contain
flush systems. Outside feed bundks are usually portable and are moved as
frequently as needed. The newer dry-lot installations have paved outside
feeding areas with shade.
Herd size in Florida varies from approximately 100 cows to about 6,000
cows. In general the dairies in South Florida tend to be larger (500-1000
cows) while the dairies in the ramining part of the state are smaller but
quite variable in size.
Table 1 shows the counties where the largest number of dairies are
located. As you may note, primary dairy areas appear to be in the Jacksonville
area (Duval, Nassau and Clay counties), the Tampa Bay area (Hillsborough,
Pasco, Mantee and Polk counties), the Okeechobee area (Okeechobee, Highlands
and Palm Beach counties) and a number of dairies near Mayo (Lafayette county),
Marianna (Jackson, Holmes and Washington counties) and Pensacola (Escambia
county) .
TABLE 1. --Florida counties with ten or more dairies
County
Number of Dairies
County
Number of Dairies
Hi 1 1 sborough
62
Polk
14
Duval
27
Jackson
14
Okeechobee
29
Palm Beach
12
Pensacola area
24
Holmes
14
Lafayette
21
Hi ghl ands
13
Pasco
15
Marion
12
Manatee
19
Nassau
11
Permanent pastures containing Bermuda, pangola, bahia and native grasses
are used quite extensively. This is especially true in many of the herds
where adquate pasture land is available and semi -complete feeds are used with
a minimum amount of hay. The importance that dairymen place on the permanent
pasture as a part of the total feed varies considerably from almost nothing
to a maximum of 60-70 pounds of pasture forage per cow per day.
20
FORAGE GRASS BREEDING AT THE UNIVERSITY OF FLORIDA
By K. H. Quesenberry
Historically, the forage grass breeding program at Florida has been con-
centrated on genetic improvement of perennial tropical grasses. Pangola
digitgrass, Digitaria decumbens Stent., an increase from a South African plant
introduction, proved to be a top forage producer on sandy flatwood soils of
central and south Florida. Utilization of Pangola is limited somewhat by lack
of winter-hardiness.
In the early 1960's, a program for genetic improvement of digitgrass was
initiated under the leadership of Dr. S. C. Schank. The objectives of this
program were improved winter-hardiness, higher digestibility, and possible seed
propagation. Dr. Schank has assembled an array of D i g i ta r i a germplasm and has
made numerous interspecific hybrids in an effort to accomplish these goals.
Two cultivars, 1 S 1 ende rstem 1 and 'Transvala' have been released from the Flor-
ida D i g i ta r i a program. One of Dr. Schank's promising new hybrids (A6-2) is
significantly higher in digestibility than all other released digitgrass
cul t i va rs .
An integral part of the forage improvement program at Florida has been co-
operative international evaluation of Florida developed germplasm. This inter-
national testing of Digitaria germplasm led to the identification of Pangola
Stunt Virus (PSV), a serious disease in several Central and South American
countries. Although this virus has not been identified in Florida pastures, it
has devastated Pangola pastures in Guyana. The cultivar Transvala is resistant
to PSV and was released for utilization both in Florida and i n te rnat i ona 1 1 y .
Dr. A. E. Kretschmer at the Agricultural Research Center, Ft. Pierce, has
tested several D i g i ta r i a introductions at this more southern location. A new
cultivar, 'Tiawain' digitgrass (_D. pentenz i i ) will be released in 1978. This
cultivar produces somewhat more dry matter in the cool season and is perhaps
better adapted for hay production than Transvala.
A program for the improvement of guineagrass, Panicum maximum Jacq. was
initiated by Dr. R. L. Smith in 1970. Guineagrass is an important forage in
many areas of the humid tropics; however, most "land" varieties are apomictic.
Dr. Smith has identified a source of sexual germplasm and has produced several
hybrids using apomictic males and sexual females. Some of these hybrids can be
stabilized as apomictic lines and several have been tested for forage poten-
tial. Guineagrass usually will not perenniate in north-central Florida and its
use will likely be limited to south Florida and the tropics.
Dr. Smith has devoted much of his research in the past three years to
studying the potential of associative N^-fixation by grass-bacteria systems.
One breeder line of guineagrass has shown a yield response to inoculation with
the bacteria Azospirillum brasilense. As a part of this research, Dr. Smith
has begun a study of the forage potential and nitrogen efficiency of swi tch-
grass, Pan i cum vi rgatum.
Limpograss, Hemarthria altissima (Poir) Staph and Hubb, was first intro-
21
duced into Florida in 1 S 6 4 . Three introductions, P.l. 299993, 29999^+, and
299995 were increased and tested over a ten year period by various forage work-
ers throughout the state. Limpograss is best adapted to the wet flatwood soils
of central and south Florida, although it has been grown successfully at Jay in
west Florida. It has superior winter-hardiness to most D i g i ta r i a introduc-
tions. An estimated 6000 to 8000 ha are currently planted to limpograss. In
1978, three cultivars (‘Redalta1, 'Greenalta1, and 1 B i ga 1 ta 1 ) were officially
released as direct vegetative increases, respectively, of the above three in-
t roduct ions.
A program of intensified selection and breeding in limpograss was initi-
ated by the author in 1976. The objectives of this program are better persis-
tence under frequent cutting, improved IV0MD, and increased early spring pro-
duction. In this selection program germplasm has been identified which is
consistently above 70% IV0MD at five weeks growth. Other lines have produced
k. 0-^.5 MT/ha of dry matter by April 20, 1978. Although limpograss is vegeta-
tively propagated, crosses are being made in an attempt to incorporate high
IV0MD, early growth, and persistence into a desirable forage type. Advanced
lines are being evaluated for persistence under grazing.
In addition to these programs with perennial grasses, Dr. Gordon Prine has
used recurrent selection for reseeding ability to develop a reseeding annual
ryegrass, Lol i urn multi f 1 orum L. for Florida and the lower South. This ryegrass
has been named 'Florida reseeding1 and is presently being increased in Oregon.
A few commercial seed are expected to be available for the 1979 fall planting
and adequate supplies for fall 1 9 80 . Florida reseeding shows superior reseed-
ing over commercial cultivars if grazing is deferred so that seed can develop
on pastures. Various annual and perennial clovers, big-flowered vetch and hop
clover have reseeded sa t i s factor i 1 v with Florida reseeding ryegrass.
22
SELECTION AND BREEDING OF LEGUMES IN FLORIDA
By Albert E. Kretschmer, Jr.
Legume selection and breeding programs for Florida forage must satisfy a
range of climatic zones from tropical to temperate.
Dr. L. S. Dunavin, ARC (Agricultural Research Center), Jay, is observing
and selecting introductions primarily of birdsfoot trefoil (Lotus corniculatus),
cicer milkvetch (Astragalus cicer) and flat pea (Lathyrus sylvestris). Major
clover emphasis is on white, red, and sub.
At Gainesville, Dr. G. M. Prine, working with perennial peanuts has se-
lected an Arachis glabrata, 'Florigraze', adapted to latitudes up to about 30°N
and to well-drained soils. It produces from 4 to 6 tons of hay annually from 2
or 3 cuts. Florigraze competes well in perennial grass sods and survives under
heavy grazing. Prine is also screening and selecting sub, arrowleaf , crimson,
persian, red and alsike clovers; and vetches, hop clovers, and seradella.
Dr. C. E. Dean, clover breeder, is releasing a new, yet unnamed, white
clover cultivar as soon as sufficient seeds are available. This variety has
superior stolon persistence during the summer, resulting in earlier fall and
winter utilization. Other work includes the identification and incorporation
of genetic resistance to viruses.
Dr. E. S. Horner's alfalfa selection work led to the release of 'Florida
66'. At present his efforts have been directed to the selection of spotted
alfalfa aphid resistance. An alfalfa population, selected for adaptation and
persistence in the Gainesville environment for eight cycles, has been screened
for aphid resistance for two cycles. The resistant population has performed
well in variety trials and is being increased for release. Work will continue
with this and two other recent releases for improved persistence and productiv-
ity.
Results of work at the ARC-Ft . Pierce has led to this year's release of
'Florida' carpon desmodium (Desmodium heterocarpon (L.)DC.), a long-lived, per-
ennial, high seed-producing, tropical legume. It competes well with tropical
grasses and persists under high grazing pressures.
At the ARC-Ft. Pierce, Dr. J. B. Brolmann, is working with the Stylos-
anthes genus including introductions of scabra , guianensis , S^. subsericea
and _S . f ructicosa . Screening of these species and natural stylo hybrids are
being evaluated for persistence, early flowering, cold tolerance, and morpho-
logical characters. Characterization and evaluation of 60 native ecotypes of
the perennial, S_. hamata , are in progress.
Dr. A. E. Kretschmer, Jr. is evaluating about 900 tropical legume ecotypes
including Macropt ilium, Centrosema, Teramnus , Desmodium , Desmanthus , Calopogo-
nium, and Aeschynomene . Particular emphasis will be in the evaluation of about
250 ecotypes of Aeschynomene for perenniation and tolerance to waterlogging.
23
GRAZING MANAGEMENT RESEARCH WITH IMPROVED FORAGES AT GAINESVILLE
By W. R. Ocumpaugh
In addition to reporting on grazing research at Gainesville, the grazing
research at Jay, Florida is to be covered.
Jay is in Northwest Florida in an area that is better adapted to growing
row crops than most of Florida. Therefore, they have limited their grazing
research to work on annual forage crops. In the past they have worked with
summer annuals, but presently they are limiting their grazing research to win-
ter annual crops. They plant winter pastures on land that is used to grow
soybeans and other summer annual row crops. They do not maintain a herd of
cattle on the station, but buy and sell feeder cattle to fit their needs.
Their most recent work involves supplemental feeding of cattle on pasture at
various rates, then taking some of these on into a feedlot situation for vari-
ous lengths of time.
Grazing research on improved forages at Gainesville is more complex than
at most research stations. We divide grazing research into at least two
phases, as part of a multiphase forage evaluation scheme. The use of this
scheme in a grass breeding program was reported to this group last year
(Quesenberry et al. 1977).
One of these phases involves the use of the grazing animal only as a de-
foliation tool. Here we study the effects of the animal on plant responses,
ie. botanical composition changes, survival and/or productivity.
Another of these grazing phases involves the more traditional method of
studying the effects of plants (forage) on the animal responses.
We presently have only one experiment of this more traditional type where
we are interested in animal performance. This experiment consists of using
summer annual forages as supplemental creep grazing for nursing calves. One
replication of the experiment is at the Pine Acres Research Unit south of
Gainesville, the other replication is on the Beef Research Unit north of
Ga i nesvi 1 1 e .
The remainder of our grazing research effort is concentrated on studies
of the effects of grazing animals on plant responses. All of this work is be-
ing conducted at the Beef Research Unit. This research is carried out using
mini-sized pastures (0.05 to 0.10 ha each).
We have one experiment which contains 82 pastures to study the effect of
grazing management in combination with other cultural treatments on a smut-
grass-bah i agrass-wh i te clover sward. Our main objective is to study the ef-
fects of these treatments on botanical composition changes of the sward, in
hopes to learn how to manage pastures infested with smutgrass.
We have a number of grazing experiments where we have planted from 10 to
30 different breeding lines and/or plant introductions of forages within one
pasture and grazed them at a set frequency using mob grazing techniques. In
these experiments, we are mainly interested in survival and general vigor af-
ter one to three years of grazing. We also estimate relative yields of these
24
forages, usually with the aid of a simple disk-meter.
We have another variation of this where we introduce frequency of animal
defoliation as a variable. In these experiments, we like to narrow the number
of forages down to 10 or less. These are usually forages that were selected
out of previous trials and constitute more advanced material in a breeding/
selection program.
Still another type of experiment where we are looking at the effect of
grazing animals on plants involves an experiment which has bahiagrass as the
base grass. Here we have overseeded plots with 'Florida reseeding1 ryegrass
and 'Gulf' ryegrass and then planted subplots to 'Nolins' red clover, 1 No 1 ins'
white clover and an advanced breeding line of 1 FS - 5 1 white clover. This ex-
periment contains 22 pastures, and we are imposing grazing management on these
that we hope will help us learn more about how to manage the ryegrass so it
will reseed and the clovers so they will live over the summer.
REFERENCE
Quesenberry, K. H., Rex L. Smith, S. C. Schank and W. R. Ocumpaugh. 1977.
Tropical grass breeding and early generation testing with grazing animals.
Proc. 3^th South. Past. For. Crop Imp. Conf. Auburn AL. pp. 100-103.
25
FORAGE RESEARCH AT ONA
By P. Mis levy
In the state of Florida there are about 34 million acres of total land
area. Approximately one- third or 12 million acres is used for some form of
pasture (native range, woodland and improved). About 4.5 million acres of
this land is used for improved and temporary pasture or forage production. At
the present time about 125,000 additional acres/year of native land is estab-
lished to improved perennial or temporary forages via the vegetable route.
Under this program land in native condition is used for 1-3 years for vegeta-
ble production, after which it is established into improved forages.
The Agricultural Research Center (ARC), Ona is located latitude 27°25'
north, longitude 8l°55' west. Climatically the weather is tropical with
temperate intrusions in the winter season. These intrusions bring repeated
frost periods having temperatures of 28°-34°F, with lower readings at less
frequent intervals. Rainfall averages 56 inches annually with over 75%
occurring from late May to mid October.
The Spodosols and associated flatwood soils found at the Ona research
center occupy 8.5 million acres in Florida. These lands are well suited for
forage production and also are used for citrus and vegetable production to a
limited extent. Some 65%, of the 2.8 million cattle found in Florida are loca-
ted within the southern 2/3 of peninsular Florida. The research program at
Ona, ARC is directed toward the need of the south central Florida cattle
industry.
Due to the diverse rainfall, temperature and edaphic conditions between
Gainesville and Ona 165 miles to the south, an intensive forage program is
conducted at Ona. This program is conducted in cooperation with forage
researchers in Gainesville and other research centers and provides much of the
forage research information needed in the more tropical areas of the state.
Forage research is conducted both at the Ona and Immokalee research center.
The latter center is 100 miles south of the Ona ARC.
Research at Ona can be categorized in the following manner:
I. Winter Annuals
Each year some 10-15 entries each of small grains, ryegrasses, clovers,
and alfalfas are tested to determine forage production, persistence, insect and
disease problems and other agronomic characteristics. Entries are tested both
at Ona and Immokalee research centers. They are seeded in November and
harvested 4 to 6 times, terminating in May or June. Forage production can
range from 3-5 T/A dry matter. Alfalfa and red clover varieties, which act as
annuals, under Florida conditions are highest yielding, and produce forage
over the longest time period of all winter annuals.
26
II. Summer Annual Grasses
Annually some 25-30 commercial corn hybrids, grain sorghums, and 10-15
entries each of forage sorghums, sudangrass x sorghum hybrids, and pearlmillets
are tested for dry matter forage yield and/or grain yield, disease resistance,
lodging and other agronomic characteristics. Most entries are tested at both
the Ona and Immokalee locations. Entries are generally seeded in February and
harvested in May, June and July, depending on species. Total seasonal dry
matter yields may range from 6 T/A for pearlmillets to 18 T/A for forage sorg-
hums. Dry matter forage yields for commercial corn hybrids generally range
from 7 to 11 T/A in 100 days, with grain yields ranging from 120 to 180 bu/A
shelled corn @ 15.5% moisture. Basic fertility programsvary from 150-100-200
to 250-100-200 lb/A N-P2O5-K2O. Irrigation is applied on all summer annual
grass studies.
III. Summer Annual Legumes
'American joint' vetch (Aeschynomene americana) , 'Hairy indigo' (Indigo-
f era hirsuta) and Alyce clover (Alysicarpus vaginalis ) are the summer annual
legumes grown in perennial grass sod and/or under cultivated conditions.
Clipping studies are presently being conducted on American joint vetch and
hairy indigo to monitor yield, quality and persistence. These legumes are
seeded in June and grazed or harvested from late August through October.
Fertility requirements are generally low with 0-30-60 lb/A N-P2O5-K2O as an
adequate fertility program. Yields are also low, ranging from 1.0 to 2.0 T/A
dry matter. Forage quality of these legumes when removed at a 12-20 inch
height is generally quite good. All three species will withstand saturated
soil conditions.
IV. Perennial Forages
Perennial forage research generally follow the forage evaluation scheme
described by Quesenberry et al(1977).
Phase I: Evaluation of plant introductions and breeder lines .- -During
this phase there are some 100-300 perennial forage entries evaluated as single
plots, with sufficient space allowed for development of stolonif erous and/or
rhizomatous plants. Entries expressing superior forage potential for a speci-
fic area are re-established in replicated plots. Forage potential is deter-
mined by forage yield, quality, persistence and vigor.
Phase II : Regional adaptation in small plot clipping trials. --All entries
studied in this phase are in replicated plots. Presently various fertility
and defoliation experiments are being conducted on Cynodon spp . , Digitaria spp.,
Paspalum notatum, and Chloris gayana . Hydrocyanic acid is also being monitored
at different fertility levels and physiological stages of growth in various
Cynodon species.
Phase III: Forage response to grazing animals . --Forage research in this
phase is conducted concurrently with phase two. When forages are selected to
be eventually used for grazing, little would be gained by conducting phase two
studies if the entry would not persist under grazing. At Ona various forms of
phase III research are presently being conducted. This phase involves mob
grazing of entries and grazing intensity studies.
The mob grazing technique involves confinement of a large number of
27
animals to small paddocks and forcing the animals to graze all entries to a
uniformly close stubble height in one to two days. At Ona, the mob grazing
technique is used as a method of screening 15-30 potential perennial forages.
These forages are planted or seeded in individual plots 25 x 25 ft, surrounded
by a 3 ft non-vegetative border. Pastures containing all of the grass entries j
are grazed at different frequencies. Rest periods of 2, 3, 4, 5 and 7 weeks
are presently being studied. Prior to each grazing, treatments are sampled
for dry matter yield, and quality. Forage persistence is also monitored
throughout the growing season. Approximately forty yearling cattle are allowed
to graze each 0.6 acre paddock. The purpose of this technique is to study the i
effect of the grazing animal on the forage entry.
The purpose of the grazing intensity experiment is to study the effect of
stocking rate on forage yield, quality, utilization and animal performance.
Three stocking rates SR (3 low), 4 (med) and 6 (high) cattle/A) were imposed
on 3 stargrass entries (Cynodon spp.) and medium SR on 'Transvala digitgrass'
(Digitaria decumbens ) and 'Pensacola' bahiagrass (Paspalum notatum) . Animal
production was highest at the medium stocking rate averaging 600 Ib/A/growing
season over a two year period.
Phase IV: Animal response to forages . --The objective is to determine
animal performance on potential perennial forages. Earlier, in phase III the
effect of animal on plant performance was studied. The measurements in phase
IV estimate animal gain per unit area, carrying capacity per unit area, volun-
tary intake, nutrient digestibility, forage quality prediction models, and
forage yield in terms of feed units. Several of the variables described here
were measured in the grazing intensity study above, indicating that certain
variables in phase III and IV may over lap. Variables in phase IV are studied
at Ona through year-long 5 acre pasture grazing experiments.
V. Other Forage Research
Multicropping - Ona. --The objective of this research is to produce two to
three crops of high quality forage per year under water control. The present
studies at Ona are divided into two parts, 1) demonstration and 2) research.
The demonstration area contains 30 acres of tillable land surrounded by a 4' x
12' rim ditch and dike used for drainage. This multidisciplinary study will
determine the physical and economic feasibility of growing several crops per
year on the same land area and providing forage for animal feeding studies.
Present multicropping research studies involve: cropping sequence studies
(determining the proper forage crop sequence combination for central Florida),
and corn-sorghum, density study, and Aeschynomene clipping study. All studies
are small plot clipping experiments in which superior treatments will be used
in demonstration areas.
Multicropping - Immokalee.-- Many cattlemen are involved directly with
vegetable production or indirectly involved through the lease of their land.
The production of forage crops in rotation with tomatoes, peppers or cucurbits
holds great potential, and the major reason is the use of residual fertility
from the previous vegetable crop. At the Immokalee ARC a research program, is
being carried out to study the production of forage crops which second as
cover crops between vegetables. One study deals with the seeding of spring
corn after fall tomatoes. Corn is drilled into the plastic mulch soon after
the tomatoes are harvested. Another study is being carried out to select corn
herbicides which are compatible with succeeding vegetable crops.
28
Sod-seeding . -- Research is presently being conducted with winter annual
grasses and legumes and summer annual legumes at Ona and Immokalee.
Experiments are designed to test seeding methods, species and herbicide
treatments. Superior treatments are tested in demonstration plots throught
central Florida.
Water Efficiency.-- This experiment is designed to determine the water-
dry matter ratios of several perennial and annual forages during the cool-dry
February through May period. In addition, water movement in a sandy soil is
monitored after each irrigation or rainfall. Correlations between tensiometer
readings at various soil depths and actual moisture are being calculated.
Phosphate reclamation.-- Due to the extensive phosphate mining in central
Florida sand tailings spoil banks and slime areas (colloidal phosphate) are in
need of reclamation. Therefore a series of studies were established to deter-
mine the optimum soil amendments required on sand tailings for good forage
production. Grass and legume entries were established on the various soil
treatments, to determine yield performance, drought tolerance, establishment
and persistence of each entry. In addition experients were established to
study the effect of plant species and fertilization on evapotranspiration as
measured by the dehydration of a slime pond (colloidal phosphate).
Pasture herbicides.-- Research is presently being conducted on several
weed species found in perennial subtropical pasture grasses. Smutgrass
(Sporobolus poiretii ) appears to be the most prevalent grassy weed. Dog fennel
(Eupatorium capillifolium) , thistle (Cirsium spp.), blackberry briers and horse
nettle (Solanum carolinense) appear to be the most troublesome broadleaf weeds,
in addition to prickly pear cactus (Opuntia spp.) in established perennial
grass pastures.
Native rangeland.-- The native range represents a valuable resource for
Florida cattlemen. Native pastures prior to 1960 were managed primarily for
pineland threeawn (Aristida stricta) , but emphasis has shifted to management
for higher producing, more palatable bluestems (Andropogon spp.), indiangrass
(Sorghastrum spp.), Panicum species, etc. Research is under-way at Ona to
support this change in management direction. Measurement of the plant response
to grazing and clipping, saw palmetto control, effect of fire and grazing,
range rehabilitation, and chemical composition studies are a few of the
research projects.
REFERENCE
Quesenberry, K. H. , Rex L. Smith, S. C. Schank, and W. R. Ocumpaugh. 1977.
Tropical Grass Breeding and Early Generation Testing with Grazing Animals.
Proc . Southern Pasture and Forage Crop Improvement Conf. 34:100-103.
29
FORAGE QUALITY EVALUATION AT THE UNIVERSITY OF FLORIDA
By John E. Moore
The overall objectives of this research program are to help make improved
forages and forage utilization systems available to Florida's ranchers and
feeders, and to provide information which will assist in making forage-
livestock management decisions. Specific objectives include the following:
1. Compare the quality of various forages in terms of animal
performance, intake and digestibility.
2. To estimate the quality of forages from small research plots in
terms of jin vitro digestion and chemical composition.
3. To improve prediction methods by developing more accurate and
rapid laboratory procedures for use in research and extension
forage testing and evaluation.
EVALUATION WITH ANIMALS
The variety of soils and climates in Florida makes it necessary to con-
duct forage evaluation research with animals at several locations in north,
central and south Florida, including Research Centers at Jay, Quincy, Ona, and
Belle Glade, and in the Gainesville area at the Beef Research Unit, Purebred
Beef Unit, Dairy Research Unit, Horse Research Unit, and Nutrition Laboratory.
Grazing trials and feedlot trials are conducted with cattle, and intake and
digestibility trials are conducted with cattle and sheep.
Permanent Grasses
Bahiagrasses , bermudagrasses , stargrasses, limpograsses (Hemarthria) ,
digitgrasses , St. Augustinegrass , and paragrass are the primary permanent
grasses under evaluation. There have been three releases in recent years:
McCaleb stargrass, Slenderstem digitgrass, and Transvala digitgrass. Cattle
grazing tropical grasses during the summer exhibit "summer slump", a period of
low average daily gains due to low intake of forage. Studies of the effects
of maturity have shown that after 8 weeks regrowth, voluntary TDN intake was
below the maintenance requirement. Grain supplementation reduced intake of
immature bermuda (substitutive) but had no effect on intake of mature bermuda
(additive) .
In the Everglades on organic soils, St. Augustinegrass was shown to be
superior to bahiagrass and although paragrass was superior to both of the
others, it was frost sensitive. Pastures and a high water table may be nec-
essary to prevent subsidence of the soil and to maintain agricultural produc-
tion in the Everglades. Pelleting of St. Augustinegrass and paragrass in-
creased voluntary intake due to an increase in rate of passage.
30
Temporary Grasses
Oats, ryegrass, wheat and triticale have been evaluated as temporary
winter pastures, and sorghum and millet are being studied as pasture and as
haylage in comparison to corn silage. With small grains, wheat was superior
to rye and triticale, and supplemental feeding on pasture was not always
profitable. Mixtures of forages including crimson clover lengthened the
grazing season and increased beef production. Several ryegrass varieties in-
cluding a tetraploid are being evaluated for intake and digestibility. The
summer annuals were found to have a short growing season and in some cases,
supplement was profitable. Corn was superior to sorghum as a silage crop and
millet haylage was not as profitable as millet pasture.
Legumes
Aeschynomene , alfalfa, clovers, perennial peanut, and Desmodium have been
evaluated. Florida 66 alfalfa, a variety developed for Florida, and a new
perennial peanut currently being evaluated, were shown to have high voluntary
intake. The perennial peanut is being released for use in permanent pastures.
Mature Aeschynomene haylage requires supplemental energy for growing steers
because it has high fiber and low digestibility. Desmodium heterocarpon grows
well in south Florida pastures and is currently being released.
Sugarcane
Sugarcane whole plant, tops and bagasse are being evaluated as animal
feed sources in the Everglades. Cane tops are suitable as a roughage source
for finishing cattle and as a supplement to winter pasture for cows. The
sugar content of whole cane depresses the digestibility of fiber and the rate
of passage from the rumen. Sugarcane bagasse may be improved by sodium
hydroxide treatment. Whole cane is being evaluated.
Aquatic Plants
Water hyacinth and hydrilla, weeds which infest Florida’s waterways, have
been evaluated as feed sources for cattle. When incorporated in complete
rations at the rate of 33% of the total organic matter, these plants were equal
to bermudagrass as a source of nutrients. However, harvesting and storage
problems limit the use of these materials at the present time.
ROUTINE LABORATORY EVALUATION
The forage evaluation laboratory in the Agronomy Department provides a
service to forage researchers throughout the state. The major techniques are
in vitro digestion and nitrogen analysis. The Ln vitro procedure involves
two-stage organic matter digestion and has a capacity of 300 tubes per week.
The nitrogen technique is automated and has a capacity of 200 determinations
per day. Phosphorus is also determined by the automated procedure and cations
are determined in the Soil Science Laboratory. The extension service provides
a forage testing and evaluation program for farmers and ranchers in cooperation
with the State Department of Agriculture and Consumer Services. Crude protein
and crude fiber are used to estimate digestible protein, TDN and net energy.
31
The in vitro procedure is the most reliable predictor of forage quality
now available, although there is a discrepancy in the in vitro and jin vivo re-
lationship with bahiagrass. Nevertheless, the technique has been useful in
comparing introductions, breeders lines and management treatments. It was
successful in predicting seasonal gains by steers grazing small grain pastures.
PREDICTION RESEARCH
Standard chemical analyses have been unacceptable as predictors of forage
quality (intake of digestible organic matter) across a wide range of tropical
grass species. Present research involves the development of rational mathe-
matical models which describe digestion and passage, and the determination
of forage characteristics which have cause-effect relationships with para-
meters in the model. Several forage characterization techniques including
physical, anatomical and chemical methods are being evaluated. Infrared re-
flectance spectroscopy is being tested to determine if it has potential for
making the numerous analyses necessary to improve acceptability of routine
forage tests.
SUMMARY
Forage evaluation research is being conducted at nine units from north
Florida to the Everglades. The wide range of climate and soil makes it
necessary to evaluate a wide range of forages and non-conventional forage
crops. A complete scope of analytical techniques is involved including animal
performance trials on pasture and in feedlot, intake and digestibility trials,
and routine in vitro and chemical analyses. Attempts are being made to im-
prove the acceptability of predictions of forage quality using laboratory
techniques .
32
N2-F I XAT I ON RESEARCH WITH TROPICAL GRASSES
By K. H. Quesenberry, R. L. Smith, S. C. Schank
The indication that significant levels of ^“fixation occur under tropical
grass cover was suggested by nitrogen balance observations carried out by
Dobereiner, 1961, 1966; Moore, 1963; and Joiyebo and Moore, 1963- Most of the
world paid little attention to this research, until the energy crisis of. the
1970's, when renewed interest in biological ^ fixation arose because of the
tremendous increases in the price of n i t rogen rert i 1 i zers .
In Brazil in 197^, Drs. Rex L. Smith and S. C. Schank saw the potential of
nitrogen-fixing associations between bacteria and tropical grass roots, partic-
ularly on 'Transvala' digitgrass. Dr. Rex Smith brought a culture of the sus-
pected nitrogen fixing microbe, then called Spi r i 1 1 urn 1 ipoferum, to Florida
and immediately began some exploratory experiments on inoculation of this bac-
teria onto the roots of several tropical grass species.
The results of these experiments raised sufficient interest at Florida in
1975 to stimulate the organization of a research team of plant breeders, physi-
ologists, and microbiologists to study this associative system.
Results of the 197^+ field inoculation experiment were verified in 1975,
with more extensive experiments which showed that yield increases were possible
at certain fertility levels on several of the tropical grasses. Data from the
1976 and 1977 inoculation experiments also showed similar trends, but a severe
drought was experienced in early summer (1977) and few statistically signifi-
cant yield increases were obtained from 1977 experiments. Since field results
have been erratic, more controlled laboratory and greenhouse experiments have
been conducted in an effort to better understand the system.
One greenhouse experiment with several genotypes of bermudagrass showed an
apparent grass genotype-bacteria strain specificity. This result supported 2
year field testing of pearl millet genotypes which produced increased yields
from inoculation of 1 Gah i a- 3 1 but not from the inoculation of its parents.
Additional experiments are underway to further study this possible genotype in-
teract i on .
We have utilized the acetylene reduction assay as a measure of potential
fixation by grass-bacteria systems. Our research has shown that the rates
are erratic and can be influenced by environmental conditions of the plants as
well as altered conditions in the assay procedure. Higher levels of acetylene
reduction were obtained in reduced oxygen environments. Acetylene reduction
rates generally did not correlate with increased yields.
Dr. M. H. Gaskins, a plant physiologist on the N research team, has shown
that Azospirillum brasilense produces growth regulating compounds. He has sug-
gested that the yield increases observed in field experiments may be due in
part to these growth substances. Dr. Gaskins has also shown that the quantity
of exudate from roots of small plants in sterile solution culture would not
support high rates of N fixation. These findings have not been tested on
plants grown under field conditions, but genetically altered bacteria strains
are being produced which should allow field testing of these findings.
33
Research is currently in progress to study environmental factors which
may influence the establishment and continuation of an associative nitrogen
fixing system. The effect of growing plants in a reduced 0 root environment
with Azosp i r i 1 1 urn inoculum is being studied. Preliminary results from this
study suggest that higher acetylene reduction rates are obtained in lower 0 .
Other studies are being planned to alter the photosynthate supply to the roots
by shading.
SUMMARY
Inoculation of certain tropical grasses with Azospirillum brasilense can
result in a significant yield increase. Most increases have been on the order
of 15~20% over uninoculated controls. Response to inoculation is often erratic
and unrepeatable, but there are some indications of a plant genotype-bacteria
strain interaction. Although Azosp i r i 1 1 urn is a nitrogen fixing microbe, it
also has been shown to produce growth regulating substances which may account
for some of the observed yield responses. The effects of various environmental
factors on the association are being studied.
[The references cited in this paper were not
received for publication. --Publisher . ]
34
SYSTEMS FOR MAKING, HANDLING, STORING
AND FEEDING LARGE HAY PACKAGES
By B. L. Bledsoe
Scarcity of labor for timely harvest — and hay quality losses from
weather damage or from excessive mechanical manipulation — are haymaking prob-
lems which have plagued farmers for years. In the early 1970's mechanical
large-package haymaking developed as one method for more timely harvest with
fewer personnel. Systems of machines were introduced to allow one person
working alone to conduct all operations necessary to harvest, transport, store,
retrieve and feed hay. However, shapes and sizes of the large packages created
problems for inside storage. Quality deterioration from outside storage caused
concern — especially for high-value legume hays commonly used for dairy opera-
tions in the humid Southeast. Consequently, experiments at various locations
have attempted to determine the extent of losses caused by large package hay-
making, storage and feeding methods, and to define new methods for reducing the
losses .
This report describes results from experiments with large-package haying
systems at The University of Tennessee and compares them with findings of other
research efforts in the Southeast and in some other regions of the nation.
The Tennessee experiments were accomplished cooperatively by the Depart-
ments of Agricultural Engineering, Plant and Soil Science, and Animal Science.
The experiments were at Ames Plantation, Grand Junction, at the Dairy Experi-
ment Station, Lewisburg, and on two private farms, one in East Tennessee and
one in Middle Tennessee. The studies emphasized machines requiring low initial
investment such that results would be applicable to small farms (less than
100 ha).
CUTTING, CONDITIONING, CURING BEFORE PACKAGING
To reduce chances for weather damage, hay should be cut and dried to the
moisture content required for packaging as quickly as possible. Conditioning
— crimping, crushing, or abrading plant stems and leaves — will hasten drying
(1,6,7,10) of both grass and legume hay. For small stemmed grasses, like the
bermudagrasses , Hellwig (7) concluded that the fluffy windrows left by con-
ditioning machines — altering the way the hay lies on the ground — had a
greater influence on improved drying rates than did the physical alteration of
the grass stems and leaves by the conditioning rolls. In criteria for an im-
proved hay conditioner for the temperate, humid climate of the British Isles,
Klinner (10) stressed the formation of a low density swath or windrow that
resists settling and is deposited on a uniform stubble capable of supporting
the cut crop to optimize air circulation.
The horizontal rotary-head tedder (Figure 1) is widely used in humid areas
of Europe as a hay conditioning device. Barrington and Bruhn (1) found that
alf alfa-brome hay tedded with this machine immediately after cutting dried
faster than untreated swaths but not so fast as hay crushed by conditioning
35
Figure 1. — Horizontal rotary-head tedder used in swath-drying studies.
o'
C
c
o
O
CD
3
73
O
CDST CDST
9/12/77 9/13/77
Figure 2. — Drying curves for five swath-drying treatments, Ames Plantation, 1977.
36
rolls and left in a swath to dry. Hellwig (7) compared a cylindrical reel
tedder with a crushing roll conditioner and found no significant difference in
drying rates for Coastal bermudagrass . He also noted that bermudagrass stems
were not adequately crushed by one pass through the rolls. This observation
led him and others to experiments with a tandem roll mower-crusher (8). Two
passes through the crusher rolls increased the drying rate of Coastal bermuda-
grass hay about 40 percent above that conditioned with only one pass. The hay
in vitro dry matter digestibility was improved significantly by the extra pass
through the conditioner rolls. However, unrecoverable forage yield (due to
breaking of grass stems into small pieces that were lost in the stubble) was
14.3% with the tandem mower-crusher, but only 10.3% with the conventional
mower-crusher; this increased loss was considered excessive.
In the Tennessee experiments, a horizontal rotary-head tedder was used to
form partially dried swaths of conditioned hay into windrows for completion of
drying. The fluffy windrows were expected to dry faster than the denser wind-
rows formed with a side-delivery rake. Three years of data show that the
fluffy windrows (cross-sectional area from 1.2 to 1.8 times that of raked wind-
rows) did not dry faster than raked windrows unless wind velocity was above
6.5 km/hr (4 MPH) and relative humidity was below 50%. Drying rates of the
five treatments compared in 1977 using Midland bermudagrass at Ames Plantation
are shown in Fig. 2. Wind velocity was great enough on September 13 to give
air circulation for faster drying in the tedded windrows, but high humidity
preceding the rainfall on that day offset the drying advantage afforded by the
wind .
Note the one-pass mow-condition-windrow treatment was the slowest to dry
on September 12. That treatment would have been slower on the following day
also, except for the more rapid uptake of moisture from the high humidity air
by the other four treatments. The one-pass mow-condition-windrow treatment is
popular with some farmers because of the economy of machine use (fewer trips
over the field), but it is the slowest way to prepare hay for packaging, as has
been reported by researchers in Wisconsin (1) and Kansas (6) and elsewhere.
In humid areas of Europe, the tedder is used to scatter and fluff hay
immediately behind the cutter. Tedding is then repeated one or two times to
get a homogeneous dry matter content within 2 days if possible (4) . Using the
tedder in this manner will increase hay particles lost in the stubble, but the
loss is considered a minor penalty for the increased drying rate. Tedding
without windrowing will be evaluated in future Tennessee experiments. Another
promising treatment to be evaluated is to partially dry conditioned hay in a
thin, wide swath, then to invert the swath without bunching or windrowing to
expose the bottom of the swath to sunlight for completion of drying.
FORMING HAY INTO LARGE PACKAGES
A wide choice of hay packaging machines is available. High density roll
balers, producing packages of 360 kg (800 lb) and 680 kg (1500 lb) with mean
wet weight density of 150 kg/m^ (9.4 lb/ft^) are the most popular machine types
used by smaller-farm operators in Tennessee. Low density roll balers making
540 kg (1200 lb) packages of 80 kg/m^ (5 lb/ft^) density and 1000 kg (1.1 ton)
compressed stack machines are other machines in use. Many larger-farm opera-
tors prefer large compressed stack machines, making stacks containing 2700 kg
(3 tons) or 5400 kg (6 tons) of hay. These large stacking units provide
efficiency in packaging and handling large amounts of hay but have purchase
prices 1.6 to 2.5 times those of the smaller stacker.
37
TABLE 1. Mean packaging capacities for three machines used with Midland
bermudagrass and Kobe lespedeza at different moisture levels
Moisture Packaging
Machine Hay Type Content Capacity*
%
1000 kg/h
r
ton/hr
Vermeer-605C
Bermudagrass
18.5
&
24.4
11.283
U
—
12-43b
Hawk- Bilt -480
Bermudagrass
18.5
&
24.4
22.73
—
25.06
Stakhand-10
Bermudagrass
18.5
6
24.4
6.30C
—
6.94C
All
Bermudagrass
24.4
15.21®
—
16'77b
All
Bermudagrass
18.5
11 . 67°
—
12.86
Vermeer-605C
Lespedeza
12.3
&
21.4
6.63a
7.31*
Hawk Bilt-480
Lespedeza
12.3
&
21.4
18. 47^
—
20.36
Stakhand-10
Lespedeza
12.3
&
21.4
4.03°
—
4.44°
All
Lespedeza
21.4
13*66b
—
15.06a
All
Lespedeza
12.3
5.76b
—
6.35b
Vermeer-605C
Both
10 0
8.96*
9.88*
Hawk Bilt-480
Both
1 ^ • J }
9 1 /.
C
J-O . J ,
20.60
—
22.71
Stakhand-10
Both
ZI . 4
Cz
Z 4 . H
5.17C
—
5.70C
All
Both
21.4
&
24.4
14'45b
15-93h
All
Both
12.3
&
18.5
8.71b
—
9.60b
All
Bermudagrass
12.3,
18.5,
13-44b
—
14*82b
All
Lespedeza
21.4
&
24.4
9.71b
—
10.70
*Means within each category having similar superscripts are not
significantly different at a = 0.05.
Data from Robertson et^ _al. , 1976 (21)
Tennessee studies compared a high-density roll baler producing twine-
wrapped rolls of 680 kg (1500 lb) (Vermeer 605C) , a low-density roll baler pro-
ducing 540 kg (1200 lb) rolls not wrapped with twine (Hawk Bilt 480) and a low-
density compressed stack machine producing stacks of 1000 kg (1.1 ton) (Hesston
StakHand 10) . Mean packaging capacities observed for these machines during one
series of experiments are listed in Table 1 (21) . Windrows for the packaging
capacity experiments contained hay from 4.3 m (14 ft)-widths of a Midland
bermudagrass field yielding 850 kg/ha (2.3 ton/ac) and from a Kobe lespedeza
field yielding 650 kg/ha (1.7 ton/ac). Operating conditions were ideal and
allowed the skilled operators to attain near maximum capacity for the machines.
The time required to wrap the high-density rolls with twine reduced packaging
38
capacity as compared to the non- twine-wrapping low-density roll baler. However,
the high density rolls could be moved from the field immediately , whereas the low-
density rolls and stacks needed to remain in the field where discharged from the
machines for a minimum of 24 hours to allow the herbage to settle and coalesce
into packages stable enough for handling.
Bale chamber losses were not evaluated in these tests. However, other
investigators have shown that large-package machines have losses greater than
conventional balers because the hay is more severely manipulated for a longer
period of time (15) . Losses of large package machines also are highly
dependent on moisture content of the hay, especially leguminous hays subject to
much leaf shattering when dry. Losses in conventional balers vary from 2 to
5% regardless of windrow size or hay moisture content, but bale chamber losses
in large-package machines vary, depending on moisture content, from 5 to 15%
with alfalfa hay. For round balers, heavy windrows of hay at maximum moisture
content for safe storage are recommended to reduce bale chamber losses. This
requirement is just opposite that for a dense roll with maximum water-shedding
ability. A denser roll develops from use of a small windrow giving more layers
or wraps per roll. A dense roll sheds water better than a looser one but pre-
vents air circulation necessary for curing hay baled at moisture content above
20 to 25% (21).
MOVING HAY PACKAGES TO AND FROM STORAGE
Various means by which one person can handle and transport large hay pack-
ages up to 1000 kg are listed in Table 2. The handling capacity (1000 kg/hr)
depends on transport distance and safe travel speed as well as on time required
for loading and unloading. Twine-wrapped rolls can be handled and transported
more expeditiously than loose rolls or stacks. When packages are moved from
storage to the feeding area, the part of the package that contacted the ground
is usually partially decayed and tends to fall off if packages are handled
roughly. Multiple-roll bale movers which rotate bales in handling — and dis-
charge them with a different surface in contact with the ground than existed in
storage — tend to result in a significant loss of hay (20) .
Renoll et al . recommended using a self-loading 2 -wheel trailer mover towed
by a pickup truck for moving single rolls distances greater then 1.6 km (1.0 mi).
However, an on-farm case study in Middle Tennessee (14) showed that the tractor
-mounted single-roll mover had greater handling capacity with less cost for
distances under 3.2 km (2 mi) than the trailer-type mover. Evidently topo-
graphy and field and road conditions have a strong influence on handling and
transport capacity (Table 3).
STORAGE OF HAY PACKAGES
A number of experiments has confirmed that inside storage of hay packages
with moisture content below 20% results in good hay quality preservation (5,15,
21). However, well-formed stacks with no depressions in the top surface^ anc}
rolls of grass hay can be stored outside on sunny, well-drained surfaces with
only small dry matter and quality losses. The packages should be spaced at
least 0.3 m (1 ft) apart for air circulation to remove moisture accumulations
after rain. Dry matter loss is dependent on type of hay, climatic conditions,
package density and moisture content of the hay when packaged.
In Missouri (5) alfalfa rolled into large bales at 36% moisture content
and stored outside lost 30% dry matter but only 19% when the rolls were stored
39
TABLE 2. Methods for handling and transporting hay packages
Description
Approximate
Handling Capacity^
Approximate
Price
1000 kg/hr
$
Trailer type mover for single roll
bale; manually operated winch
1.8
600
Tractor-mounted (3-point hitch) mover
for single roll bale
4
250
Tractor-mounted (front-end loader
attachment) mover for single bale
4
250
Tractor-mounted (3-point hitch) mover
for 1-ton stacks
6.5
900
PTO-driven roll bale pickup and trans-
port trailer (3 to 4 roll capacity)
6.5-8
4500
Average transport distance of 1.3 km (0.8 mi) calculated from data in
references (3) and (20).
TABLE 3. Capacity of low-cost, one-roll transport methods
Method
Capacity for
Different Haul Distances
0.8 km ^
1.6 km^ 3 . 2 km +
1000 kg/hr
3-point hitch or front
end loader attachment
for tractor
6.5
2.2 1.6
Truck towed 2-wheel
trailer mover
2.7
1.8 1.5
^Data from Merritt, 1978 (14); 4-wheel drive pickup truck used.
•^Data from Renoll et_ aH, 1977 (20).
1 km = 0.62 mi
1000 kg = 1.1 ton
40
Outside Storage
46.5% Initial Moisture Content
TIME (DAYS AFTER PACKAGING)
Figure 3. — Change of internal temperature with time of high-initial-moisture
Midland bermudagrass hay in high-density rolls.
inside for 6 months. Peak measured internal temperature after the 7th day of
storage for rolls stored inside on end with 2 m (6.6 ft) center-to-center
spacing was 61 C (142 F) and temperatures above 38 C (100 F) persisted for 80
days. Rolls stored outside had peak internal temperature of 67 C (153 F), but
temperatures above 38 C (100 F) persisted for only 74 days. Digestible protein
content of the hay decreased rapidly during the first 6 days of storage, when
bale temperatures — indicative of microbial activity — were highest, then
stabilized. The digestible protein decrease for hay in rolls stored inside was
3% (from 14 to 11%), and in rolls stored outside 4% (from 14 to 10%). In con-
trast to the high moisture alfalfa, fescue hay baled at 24.5% moisture had dry
matter losses of 3.3% in rolls stored inside and 13.9% in rolls stored outside.
In Nebraska (23) experiments indicated the nutritive value of alfalfa hay
could be maintained in compressed stacks (74 kg/nT (4.6 lb/ft3) dry matter
density) when packaged at moisture contents up to 40%. In Montana (12) alfalfa
hay was formed into 2700 kg (3 ton) and 5400 kg (6 ton) low-density compressed
stacks at moisture contents ranging from 18 to 53% and into 500 kg (0.6 ton)
high-density rolls at moisture contents ranging from 14 to 39%. The packages
were stored for 3 months and monitored for hay quality changes. The results
indicated storage losses were less at higher moisture but lower density.
41
An Iowa experiment (15) with mixed alfalfa-clover hay determined that dry
matter loss increased with an increase in initial moisture content of large hay
packages, but packages stored outside had dry matter losses of less than 5%
when initial moisture content was no greater than 40%. Dry matter loss
increased markedly when package maximum temperature exceeded 49 C (120 F) .
After a six-month storage, large rolls of hay with plastic caps over the upper
2/3 of the surface contained the best quality hay.
In the more humid climate of Alabama, Renoll et_ al . (18) found that low-
density compressed stacks had dry matter losses of 14%, but a large part of the
loss was due to decay of hay in contact with the ground during storage.
Similar results occurred with storage of high-density roll bales (19).
In an Indiana experiment (17) outside storage of hay packages on a 15 cm
(C in) layer of crushed stone resulted in 10% less storage loss than when the
packages were stored on sod.
Initial experiments in Tennessee with large package haymaking (1972-73)
indicated that quality of high moisture (22-30%) Midland bermudagrass hay was
preserved better in low-density than in high-density packages (9) . Outside
storage of high-moisture packages led to better quality than inside storage
where rolls were closely spaced in the barn. Bale internal temperatures of
high-density rolls packaged at 46.5% moisture content are compared for inside
and outside storage in Fig. 3. Air circulation around packages stored out-
side resulted in more rapid initial cooling.
In later experiments (1973-74) large packages of Midland bermudagrass and
Kobe lespedeza (21) were compared. At equal initial moisture contents, the
lespedeza hay packages had greater internal temperatures than the grass hay —
indicative of greater microbial activity. Effect of initial moisture content
on package internal temperature for lespedeza hay is shown in Fig. 4. Those
lespedeza packages made from hay of 23% initial moisture content had internal
Figure 4. — Curing temperatures for high-and low-moisture lespedeza hays at sev-
eral package densities.
42
Figure 5. — Mean curing and ambient air temperatures for three package types of
of bermudagrass and lespedeza high-moisture hays.
O
UJ
GO
cn
LU
iD
c
LU
O
cn
LU
Q_
Figure 6. — Percentage of hay refused from three package types when fed in slid-
ing gate feeders.
43
temperatures above 49 C (120 F) for 3 days, whereas internal temperatures for
packages made from hay with 15% moisture content never exceeded 38 C (100 F).
A comparison of the mean curing temperatures of bermudagrass and lespedeza
hays at 23% moisture content shows the effect of package density on curing
rate (Fig. 5). Internal temperatures of the low-density packages responded to
marked changes in ambient air temperature; high-density package internal tem-
peratures did not. This difference resulted from air flow through the more
permeable low-density hay.
A waterproof thatch was not formed readily on the outer surface of the
lespedeza packages, unlike in grass hay packages. Thus lespedeza hay was pre-
served better in high-density packages than in low-density ones. Quality was
preserved better with inside storage of lespedeza packages than with outside
storage (Fig. 6).
Three storage methods — inside, outside on automobile tires, outside on
ground — were compared for alf alf a-orchardgrass hay in high-density rolls at
the Dairy Experiment Station (2). Mean initial moisture content of the hay
was 11.5% and package dry matter density was 120 kg/m3 (7.6 lb/ft3). Consump-
tion of hay by lactating Jersey cows for each storage method is summarized in
Table 4. Note the advantage in dry matter preservation resulting from placing
rolls on automobile tires for outside storage. Weathered hay for the rolls
stored outside extended 20 cm (8 in) radially inward from the surface. Peak
package internal temperature for rolls stored outside was 52 C (125 F) and 54 C
(129 F) in rolls stored inside.
FEEDING LARGE HAY PACKAGES
Large hay packages offered unrestricted to cattle in the open field
resulted in excessive losses — up to 45% of package wet weight (18) . The use
TABLE 4. Dry matter losses in high-density rolls of alfalfa-
orchard grass hay
Dry Matter
Stored
Stored
Outside
Inside
On Tires
On Ground
%
Losses in Storage
3.4
11.9
16.0
Losses from Refusal
and Waste
3.7
14.1
17.4
Apparent Consumption
92. 9a*
74. 0b
66. 6b**
^Difference in values followed by the same superscript
are not significant at a = 0.05.
**Difference between rolls stored on tires and on ground
was significant at a = 0.10.
Data from Baxter, al. , 1978 (2).
44
TABLE 5. Feeding losses from large rolls of sorghum-sudangrass
hay fed with and without circular panels
Treatment^
Dry Matter Feeding Losses
By Refusal
From Trampling
Total
%
No panel, roll axis horizontal
24.3
3.6
27.9
Panel, roll axis horizontal
6.5
2.9
9.4
Panel, roll axis vertical
5.4
2.7
8.1
+500 kg (1100 lb) rolls of
density of rolls when baled was
34.5% moisture
84.7 kg/m3 (5.
content when baled;
3 lb/ft3); dry matter
dry matter
loss
during 6-month storage was 14.2%.
of feeding panels, bunks, or racks for feeding large hay packages can reduce
these losses. Parson et al. (17) noted that unrestricted feeding of large
grass hay packages to beef cows required 10.9 to 12.9 kg (24 to 28 lb) of dry
matter/cow day. With racks the hay requirement dropped to 9.2 kg (20 lb) dry
matter/cow day.
The type of feeding equipment required depends on climate. Where feeding
areas are dry (or frozen) fields, panels that cattle can push toward the hay
package as they eat are required for large stacks. For roll bales, either
circular or rectangular fixed-geometry panels that encircle the bale are satis-
factory for dry feeding areas. Slanted-bar access openings keep cattle from
backing away from the racks while eating and pulling hay ouside where it can be
trampled. Dry matter losses when feeding sorghum-sudangrass hay in large rolls
to non-lactating dairy cows on a private farm in East Tennessee (22) with
feeding-panels were one-third those measured when feeding rolls without
panels (Table 5) .
In muddy feeding areas and during rainy weather, trampling losses with
floored and covered feed bunks were kept below 5% during feeding trials con-
ducted during the rainy month of December, 1974 at Ames Plantation (21).
FUTURE DEVELOPMENT IN HAYMAKING
Large hay packages can be made, handled and fed efficiently by one person.
However, with hay of low moisture content, excessive losses occur from manipu-
lation of the hay by the packaging machine pickup and bale chamber mechanisms.
To overcome this problem, two approaches have been proposed by investigators
and machinery manufacturers: (1) make large rectangular balers with hay manip-
ulation mechanisms similar to those of small rectangular balers, or (2) make
large rolls and stacks from high-moisture hay (35 to 45% wet basis) to prevent
leaf loss during manipulation. To preserve the high moisture hay, addition of
chemical preservatives (11,13), ventilation of the package, or drying with
heated air have geen suggested.
45
SUMMARY
Large package haymaking allows one person, with suitable equipment, to
carry out packaging, handling, storing, and feeding. With such a system,
accelerated drying of the hay in the swath before packaging is still important
to avoid weather damage to the hay.
Storage losses associated with use of large package hay depend on climate,
type of hay, package density, and moisture content of the hay when packaged.
In humid climates, such as in Tennessee, grass hays can be packaged into low-
density rolls or stacks at moisture contents in the range of 20 to 30% (wet
basis) with low dry matter and quality losses when stored outside. Leguminous
hays required high-density rolls or stacks at moisture content below 20% for
quality preservation when stored outside. Storing packages on crushed stone
or on old automobile tires to avoid contact with the soil will reduce decay and
dry matter losses in the package.
Transporting large hay packages with minimal losses is best done with
machines that do not rotate the package and that deposit it in the same posi-
tion relative to the ground after transport as it was before the move. For
small-farm operators, roll-bale mover attachments for tractor 3-point hitch or
front-end loader are more economical for haul distances up to 3.2 km (2 mi)
than self-loading trailer movers. The trailer movers, however, are more
economical for distances greater than 3.2 km (2 mi).
To avoid losses from leaf shattering during the prolonged and aggressive
manipulations characteristic of present large hay-packaging machines, manufac-
turers and investigators are developing large rectangular balers and means for
either drying or using chemicals to reduce bacterial action in large packages
of high-moisture hay.
REFERENCES CITED
1. Barrington, G. P., and H. D. Bruhn. 1970. Effect of mechanical forage-
harvesting devices on field curing rate and relative harvesting losses
Trans. ASAE. 13:874-878.
2. Baxter, H. D., B. L. Bledsoe, M. J. Montgomery, and J. R. Owen. 1978. ,
Comparison of methods of handling orchardgrass hay on storage losses and
milk production of Jersey cows. Paper presented at the Amer. Dairy Sci.
Assn. Annual Meeting. East Lansing, MI, July 9-13.
3. Bledsoe, B. L. , H. A. Fribourg, J. B. McLaren, J. M. Bryan, J. T. Connell,
K. M. Barth, and M. E, Fryer. 1973. A comparison of the harvesting
characteristics of large hay packages with those of conventional bales.
ASAE Paper No. 73-1576.
4. Bosma, A. H. , F. Coolman, and M. G. Telle. 1977. Mechanization and
automatic control in forage handling. Proc . Intern. Grain Forage Harv.
Conf. ASAE Pub. 1-78:239-241.
5. Currance, D. H. , S. W. Searcy, and A. G. Matches. 1976. Large bale
storage losses. ASAE Paper No. 76-1510.
6. Fairbanks, G. E. and G. E. Thierstein. 1966. Performance of hay condi-
tioning machines. Trans. ASAE. 9:182-184.
46
I
7. Hellwig, R. E. 1965. Effect of physical form on drying rate of Coastal
bermudagrass . Trans. ASAE. 8:253-255.
8. Hellwig, R. E. , J. L. Butler, W. G. Monson, and P. R. Utley. 1976. A
tandem roll mower-crusher. Trans. ASAE. 20:1029-1032.
9. Kilgore, W. L. 1973. Moisture level effects on three packaging and
handling systems for Midland bermudagrass hay. Unpublished M.S. Thesis
The University of Tennessee, Knoxville, TN, 37916.
10. Klinner , W. E. 1976. A mowing and crop conditioning system for temperate
climates. Trans. ASAE. 19:237-241.
11. Klinner, W. E. and M. R. Holden. 1977. Advances with chemical preserva-
tives for hay. Proc. Intern. Grain Forage Harv. Conf . ASAE Pub. 1-78:
303-307.
12. Larson, W. E. , and R. L. Ditterline. 1978. Storage properties of large
package hay systems. ASAE Paper, Montana State University, Bozeman, MO.
13. Lechtenberg, V. L., M. R. Buettner, D. A. Holt, C. B. Richey, and
S. E. Parsons. 1977. Hay preservation by anhydrous ammonia treatment.
Proc. Intern. Grain Forage Harv. Conf. ASAE Publ. 1-78:327-328,338.
14. Merritt, M. T. 1978. Comparison of two low-cost single unit large bale
movers. Unpublished Special Problem Rep. Agric. Eng. Dept., The Univer-
sity of Tennessee, Knoxville, TN 37916.
15. Marley, S. J. , C. Wilcox, and M. M. Danley. 1976. The storage charac-
teristics of large round bales. ASAE Paper No. 76-1509.
16. PAMI Evaluation Tests Nos. ED-176 A, B, C. 1977. Prairie Agricultural
Machinery Institute, Humbolt, Saskatchewan, SOK 2A0, Canada.
17. Parsons, S. D. , V. L. Lechtenberg, D. C. Petritz, and W. H. Smith. 1977.
Storage and feeding of big package hay. Proc. Intern. Grain Forage Harv,
Conf. ASAE Pub. 1-78:290-292,
18. Renoll , E. S., W. B. Anthony, L. A. Smith, and J. L. Stallings. 1971.
Comparison of baled and stacked systems for handling and feeding hay.
Auburn Univ. Agric. Exp. Sta., Prog. Rep. No. 97.
19. Renoll, E., W. B. Anthony, L. A. Smith, and J. L. Stallings. 1976. Hay
in round packages and in conventional bales. Trans. ASAE 19:448-459, 454.
20. Renoll, E. L., A. Smith, J. L. Stallings, and D. L. Hess. 1977. Machine
systems for handling and feeding round bales. Proc. Intern. Grain Forage
Harv. Conf. ASAE Pub. 1-78:296-299.
21. Robertson, D. R. , B. L. Bledsoe, J. B. McLaren, H. A. Fribourg,
J. M. Bryan, and J. T. Connell. 1976. A comparison of lespedeza and
Midland bermudagrass hays when harvested, handled and fed in large pack-
ages. Paper presented ASAE Southeast Region Meeting, Mobile, AL .
47
22.
Walton, D. C. Jr. 1978. A comparison of feeding systems for use with!
large round bales of sorghum Sudan hay. Unpublished Special Problem
Report. Agric. Eng. Dept., The University of Tennessee, Knoxville,
TN 37916
23. Weeks, S. A., F. G. Owen, and G. M. Petersen. 1975. Storage charac-
teristics and feeding value of mechanically stacked loose hay, Trans .
ASAE. 18:1065-1069.
I
48
EVALUATING FORAGE CHARACTERISTICS USING A DYNAMIC MODEL OF FIBER DISAPPEARANCE
IN THE RUMINANT
By D.R. Mertens and L.O. Ely
INTRODUCTION
The objective of many forage evaluation programs in animal science and
agronomy is to assess forage quality from data on chemical and physical
characteristics of the feed. Although many factors have been suggested and
evaluated as determinants or indicators of forage quality, most have been
discarded or found to be of limited use when used as the sole index of
forage nutritive value. This suggests that accurate assessment of forage
quality must include the interactions of the animal and its microorganisms
with the chemical, morphological and physical properties of forages and the
end-products resulting from their utilization.
Since it may not be feasible to measure and evaluate all relevant factors
and interactions involved in forage quality in a single experiment, it was
concluded that modeling and simulation can offer an excellent opportunity to
delineate the role of animal and plant characteristics in forage fiber diges-
tion. A model of forage fiber digestion could provide information about di-
gestibility, intake, end-product production and nutrient utilization. Digest-
ibility can be easily related to the digestive mechanism because it is a
function of the kinetics of digestion and passage (3,29,46). Intake of forages
is related to fiber digestion because it is limited by the rate of disappear-
ance of material from the digestive tract (11,16,17,29,39,45). Recent re-
search suggests that rate of digestion or passage influences the proportion of
end-products (volatile fatty acids) produced during fermentation in the rumen
(23).
A dynamic, mathematical model was developed to include the kinetics of
passage, particle size reduction and digestion to describe the disappearance
of forage fiber from the digestive tract of ruminants. The objectives of
model development were: (1) to determine if current theories of digestion,
passage and particle size reduction could be described adequately by mathemat-
ical equations and combined into a model to estimate fiber disappearance from
the digestive tract; (2) to identify aspects of ruminant digestion and forage
characterization where current concepts or data are inadequate; and (3) to
test hypotheses regarding plant and animal factors influencing forage quality.
The model will be described and used to assess quantitatively the factors
affecting the digestion of alfalfa and Coastal bermudagrass .
MODEL DEVELOPMENT AND PARAMETER ESTIMATION
The model was developed by deriving a series of differential equations
that described theoretical relationships concerning digestion, passage and
particle size reduction. Each submodel (digestion, passage or particle size
reduction) was developed to represent, as simply as possible, current concepts
49
of animal physiology and plant characteristics; yet to include the features of
applicability, accomodation, manageability, and output comparability suggested
by Baldwin et ad. (5) . The model was implemented on the computer using the
Continuous System Modeling Program (CSMP) . The model was verified to assure
the accuracy of mathematical formulation and computer programming in implement-
ing the model and was validated by comparing model output to research observa-
tions .
Passage Submodel
The basic submodel is a sequential compartmental system proposed by
Blaxter et_ _al. (9) and Brandt and Thacker (10). This model assumes that
Rk^.lk£b»F5 where F is material excreted in the feces and R and I are digestive
compartments in the animal. Coombe and Kay (15) and Grovum and Williams
(20, 21) suggest that the I compartment is the large intestine and kg repre-
sents the rate of passage of material from the large intestine to the feces,
leaving compartment R to represent the rumen and k7 to represent the rate of
passage (or escape) of material from the rumen to the large intestine. The
passage of material through the omasum, abomasum and small intestine is assum-
ed to be a linear process that has no first-order kinetic properties. Data
of several researchers (9,15,20,21,22,27,34) were combined and interpolated
to obtain ruminal escape and large intestine rates of passage.
Particle Size Reduction Submodel
It is evident that when long forages are fed particle size reduction
must occur before fiber particles escape from the rumen. Ulyatt e_t al_. (41) ,
Troelsen and Campbell (40) and Van Soest (44) showed that average particle
size decreases as material passes from feed to rumen contents to abomasal con-
tents or feces. Although it may be possible to describe fiber particles in
the rumen by a normal, or log-normal, distribution, observation of stratifica-
tion of matter in the rumen suggests that the rumen is not a homogenous mass
of fiber particles (13) . In addition, the observation that large particles
do not pass out of the rumen suggests that the rumen must contain at least
two pools of fiber particles — one pool of large particles that must be reduced
in size before passage and another pool of small particles that can escape
the rumen.
The basic rate of passage submodel was modified by dividing the rumen
compartment (R) into large (RL) medium (RM) and small (RS) particle subcom-
partments. Three subcompartments were chosen based upon the research of
Matis (27) which indicated that fecal marker excretion was most accurately
predicted when three subcompartments were used. In addition, Ulyatt et al .
(41) and Evans et_ aT. (18) reported similar trimodal distributions of particle
sizes in rumen contents. The inclusion of a medium size particle subcompart-
ment also permits the passage of some particles that are larger than those in
small particle pool. Van Soest (44) reported that mean fecal particle size
increases with increasing intake in dairy cows. Incorporation of this con-
cept in a two subcompartment system would require the possibility that very
large particles escape the rumen.
Particle size reduction between compartments was assumed to follow first
order kinetics RL^4-»RM^5->RS . The model was further modified to allow feed
entering the rumen to enter RL , RM, or RS depending upon the proportion of
50
the feed that was of large, medium or small size. In addition, some medium
particle (RM) material was allowed to escape from the rumen but the rate was
very slow. The data of Evans et: al. (18) were used to determine rate of parti-
cle size reduction and the relative distribution of the three subcompartments
in the rumen.
Digestion Submodel
The basic model for rate of digestion was first described by Waldo (29),
who postulated that forage fiber could be divided into digestible and indiges-
tible fractions and that rate of digestion of the digestible fraction might
exhibit first-order kinetic behavior. Although the concept of an indigestible
fiber fraction is not accepted by all researchers, several in vitro and in
vivo experiments indicate that digestion reaches a maximum that does not equal
100% (6,29,36,45,49) and that probably at least the lignin component of fiber
is not completely digested in ruminants.
Smith et_ al_. (35,36) used 72 hr in vitro indigestibility to estimate the
indigestible fraction and determined rates of neutral detergent fiber (NDF)
digestion in several forages. Mertens and Van Soest (30) observed that some
digestion occurs beyond 72 hours; thus the 72 in vitro estimate will overes-
timate indigestibility. Although the mean time that material remains in the
rumen is 40-60 hours, approximately 10-25% of forage fiber remains in the
rumen for more than 70 hours. When the maximum extent of digestion is deter-
mined and used to define the indigestible fraction (C) , overall digestion is
more accurately predicted by assuming that the digestible fraction contains
fast-digesting (A) and slow-digesting (B) compartments. Dividing fiber into
three fractions is supported by the recent research of Akin et al. (1,2),
which suggests that forage plants have three morphological tissue types which
have different rates of disappearance. They observed that mesophyll and
phloem tissue were fast-digesting, bundle sheaths and epidermal cells were
slow-digesting, while lignified vascular bundles and sclerenchyma tissues
were relatively indigestible.
Rates of digestion and proportion of fiber in fast-digesting, slow-diges-
ting and indigestible fractions were obtained from Mertens (29). Since the
effect of particle size upon rate of digestion has not been clearly defined,
it was assumed that digestion rate would be the same for all particle sizes
in the rumen. Although Ulyatt e_t a_l. (42) have suggested that celluloytic
activity in the large intestine is equal to or greater than that observed in
the rumen, the digestion rate of fiber in the large intestine was assumed to
be 90% of that of the rumen because fiber reaching the large intestine would
be more refractory to digestion than that present in the rumen.
Complete Model
The complete model of fiber disappearance from the digestive tract of
ruminants is given in figure 1. Rates of particle size reduction, passage
and digestion have been integrated in a complete model of fiber disappearance.
The model was described by 20 differential equations and implemented on the
computer using CSMP. The output from CSMP gives the pool sizes (amount of
fiber in each subcompartment) and fluxes (amount of material passing between
compartments per unit of time) of fiber as it passes through the digestive
system. Starting with initial estimates of the pool sizes and given rates of
51
CO
w
o
w
p-l
w
23
M
H
c n
W
H
23
M
IS
W
Q
M
cn
O
a
52
Figure 1. Block diagram of the model of fiber dynamics through the entire digestive tract of the
ruminant. Legend: A = fast-digesting fraction, B = slow-digesting fraction, C = indi-
gestible fraction, D = digested, E = consumed, F = feces, I = intestines, L = long,
M = medium, R = rumen, and S = small.
disappearance, the model soon reaches steady state conditions for each set of
forage kinetic characteristics used. At steady state the amount of material
eaten (E) per unit of time equals the amount digested and appearing in the fe-
ces (D + F) per unit of time. The pool sizes at steady state then represent
the average amount of material that would be found in the various segments of
the animal's digestive tract.
The model was evaluated by simulating the effects of feeding a 500 kg
steer at the forage intake level of 2% of body weight per day. Input was pro-
vided as 24 hourly feedings of equal size during each simulated day. Steady
state conditions for fiber content, digestion and excretion pool sizes were us-
ually reached within 1 to 2 simulated days after rates of digestion or propor-
tion of indigestible neutral detergent fiber were changed. Time required for
adaptation of the simulated steer depended upon the magnitude of the change in
diet. Changing complete diets required 2 to 6 simulated days before steady
state conditions were attained, corresponding to times typically needed by an-
imals to adapt to similar changes in rations. All data presented in this paper
were obtained from steady state conditions.
The complete model was used to simulate NDF digestibility (NDF Dig) , per-
centage of total digestion that occurred in the rumen and amounts of NDF in the
various model pools. Rates of passage and particle size reduction shown in
figure 1 were held constant as follows: Particle size distribution; k=.85 or
.00, k2=.05 or .10, and k3=.10 or .90, for long or pelleted forage, respective-
ly: Particle size reduction and passage; k4=.07, k^=.14, k6=.006, ky=.035,
and kn=.08. Dry matter digestibility (DMD) was calculated from the summative
equation of Goering and Van Soest (19) :DMD= . 98(100-NDF)+(NDF Dig) (NDF)-12.9.
Predicted maximum dry matter intake was calculated based upon the assumption
that the maximum rumen fill capacity of a 500 kg steer would be 7.92 kg of NDF
(29) . By simulating total rumen NDF from all pools at various intakes of dry
matter the relationship between total rumen NDF and intake was derived and sol-
ved for 7.92 kg of NDF to obtain the predicted maximum dry matter intake.
Maximum digestible dry matter intake was derived by multiplying the predicted
maximum dry matter intake by the dry matter digestibility coefficient thereby
obtaining an estimate of the maximum amount of available energy that would be
consumed by the animal.
Since rigorous validation of the model was impossible because no data are
available where all, or even a majority, of the variables were measured, the
complete model was validated by comparing model output to several sources of
published research observations. The model was accepted as valid because it
could accurately predict fiber digestibility, fiber and lignin contents of var-
ious gut segments, lignin turnover times, rate of passage and dry matter intake
(3,4,7,8,11,12,24,25,26,28,31,33,37,38,43,47,48). Acceptance of the model was
supported by the observation that the original estimates of differential equa-
tion coefficients, which were obtained from a variety of ini vitro and iri vivo
experiments, required very little fine tuning to obtain output comparable with
experimental observations.
FACTORS AFFECTING FORAGE QUALITY
Two forages, alfalfa and Coastal bermudagrass , were selected for simula-
tion to assess the factors affecting forage quality. The composition and ki-
netic values presented in table 1 represent the average of 39 alfalfa and nine
Coastal bermudagrass samples (29). The crude protein and neutral detergent
53
TABLE 1. CHEMICAL COMPOSITION AND KINETIC CHARACTERISTICS OF
TYPICAL ALFALFA AND COASTAL BERMUDAGRASS FORAGES USED
IN SIMULATION EXPERIMENTS
CHARACTERISTIC
COASTAL
ALFALFA BERMUDAGRASS
Crude protein (% dry matter)
18.5
16.6
Neutral detergent fiber (% dry matter)
46.6
70.0
Acid detergent fiber (% dry matter)
36.3
34.7
Permanganate lignin (% dry matter)
9.7
5.4
Fast-digesting fraction (% NDFa)
42.4
51.7
Fast-digesting rate (hr--*-)
.1012
.0919
Slow-digesting fraction (% NFDa)
9.6
15.2
Slow-digesting rate (hr--*-)
.0190
.0224
Indigestible fraction(% NFDa)
48.0
33.1
Percentage of the neutral detergent fiber.
54
fiber (NDF) contents of these forages indicate they are high quality (14) .
The primary differences between alfalfa and Coastal bermudagrass are in NDF and
lignin contents and the proportion of NDF that is slow-digestiing . Alfalfa
contains less NDF than Coastal bermudagrass but the NDF is more lignified and
contains a smaller slow-digesting fraction.
Effect of Physical Form of the Forage
The effect of processing forages to alter physical form by grinding and
pelleting is shown in table 2. The model predicts that digestibility of both
alfalfa and Coastal bermudagrass are decreased by grinding and pelleting. This
effect observed by many researchers (3,7,8,24,25,26,31,33,38,45,48), has been
attributed to reduced retention time in the rumen, i.e., increased rate of pas-
sage out of the rumen. This hypothesis agrees with the model which predicts
that NDF and lignin turnover or retention times in the rumen are decreased by
pelleting. Dry matter digestibility was decreased to a greater extent by pel-
leting Coastal bermudagrass then by pelleting alfalfa. This result could be
due to differences in NDF content between the forages. Alfalfa contains less
NDF than Coastal bermudagrass and the use of the summative equation of Goering
and Van Soest (19) to predict DMD permits changes only in the fiber portion of
the forage to alter DMD while the non-NDF fraction is held constant at 98% di-
gestibility. However, the difference between alfalfa and Coastal bermudagrass
in digestibility depression due to processing could be due to differences in
quality between the forages (31) .
Processing forage also alters the site of fiber digestion. The model pre-
dicts that approximately 93% of the digestion of long forage fiber occurs in
the rumen. This agrees with reported ruminal digestions of NDF or cellulose
fed as long forage that range from 85 to 100% alfalfa (24,26,38) and 81 to 94%
for grasses (8,26,43). The model predicts that 84% of the pelleted forage fi-
ber is digested in the rumen which compares favorably with reported values of
60 to 94% for alfalfa (24,26,38) and 75 to 89% for grasses (8,26,43).
As shown in table 2, model simulation indicates that pelleting these for-
ages results in less fiber fill in the rumen which permits greater maximum
dry matter intake if rumen volume were the factor limiting intake, Simulation
results also suggest that the amount and proportion of fiber in the intestines
increases when forages are pelleted, agreeing with the observations of Hodgson
(25) and O'Dell et. aH. (33) which suggest that capacity of the lower digestive
tract does not limit the intake of long forage.
Increased intake appears to be the major factor in improved performance
observed when roughages are ground and pelleted (7). Although it is generally
accepted that less response is expected from pelleting a high quality forage
than a low quality one, simultion results suggest that alfalfa has a larger
intake response (1.41 units) than Coastal bermudagrass (1.02). There is little
data supporting the generally accepted concept that pelleting high quality for-
ages obtains less response than low quality forages (7) although many of the
small responses from pelleting high quality forages can be explained by intake
limitations imposed by energy demands of the animal. The data of Minson and
Milford (31) and Weston and Hogan (48) support the results of model simulation
that intake of high quality forages is improved to a greater extent than low
quality forages. Weston and Hogan (48) observed that intake was increased 1.16
units for alfalfa and .68 units for wheaten hay when the forages were pelleted.
55
TABLE 2. EFFECT OF PHYSICAL FORM OF FORAGES UPON THE DIGESTION, FIBER
TURNOVER TIMES, FIBER CONTENTS OF THE DIGESTIVE TRACT AND
MAXIMUM DRY MATTER INTAKE DETERMINED BY SIMULATION
Variable3
ALFALFA
Long Pelleted
COASTAL
BERMUDAGRASS
Long Pelleted
NDF^ Digestibility (%)
46.3
41.8
58.9
52.8
NDF^ Digestion Occurring in Rumen (%)
93.7
84.0
93.0
83.2
Dry Matter Digestibility (%)
61.0
58.9
57.7
53.5
Rumen NDF^ Content (kg)
5.51
3.70
7.01
4.82
Rumen NDF^ Turnover Time (hr)
28.4
19.1
24.0
16.5
Rumen Lignin Turnover Time (hr)
45.8
29.4
45.8
29.4
Intestinal NDF^ Content (kg)
1.30
1.42
1.50
1.74
Maximum Dry Matter Intake (% BWC)
2.87
4.28
2.26
3.28
Max. Dig. Dry Matter Intake (%! BW^)
1.75
2.52
1.30
1.75
aAll values except intake were simulated for a 500 kg steer consuming
10 kg of forage dry matter daily
^Neutral detergent fiber
Percentage of body weight consumed daily by a 500 kg steer.
56
Effect of the Indigestible Fraction of Forages
Understanding the plant characteristics that influence digestibility and
intake is important in developing new methods for evaluating forages and im-
proving their utilization. Lignin is generally accepted as the primary anti-
quality factor that inhibits the utilization of fibrous carbohydrates in for-
ages (32). Recently, Smith ct al. (36) and Mertens (29) observed that lignin
content of the plant is most highly associated with the indigestible fraction
of NDF. If this relationship is causal, the effect of lignin upon animal per-
formance can be demonstrated by changes in the indigestible fraction of NDF.
Table 3 presents the simulation results when the indigestible fraction of
NDF was increased or decreasd 8.1% for alfalfa and 21.1% for Coastal bermuda-
grass. As expected, increasing the indigestible fraction decreased digesti-
bility. It also increased the contents of NDF in the rumen and intestines
and resulted in decreased maximum dry matter intake. A 16.2% decrease in the
indigestibility fraction of alfalfa produced a 5.6% increase in digestibility
and 9.8% increase in intake resulting in a 15.4% increase in maximum digesti-
ble dry matter intake. A 42.3% decrease in the indigestible fraction of
Coastal bermudagrass obtained a 18.2% increase in digestibility and a 25.2%
increase in intake which resulted in a 43.8% increase in maximum digestible
dry matter intake. Thus, a one percent decrease in the indigestible fraction
results in a 1.0% increase in maximum digestible dry matter intake.
Effect of Fiber Digestion Rate
Crampton (17) and others (16,39,45) suggested that rate of digestion is
important in assessing forage quality, especially voluntary intake. It was
postulated that increased disappearance of fiber from the digestive tract by
more rapid rate of digestion would free space for additional intake. The ef-
fect of changing rates of digestion were simulated (table 4). Rates of fast-
and slow-digesting fractions were increased or decreased 15% for both alfalfa
and Coastal bermudagrass. A 30% increase in digestion rates resulted in a 1.5
or 3.6% increase in dry matter digestibility, a 4.5 or 7.5% increase in in-
take resulting in a 6.3 or 10.8% increase in maximum digestible dry matter in-
take for alfalfa and Coastal bermudagrass, respectively. Thus, a one percent
increase in digestion rates results in a 0.6% increase in maximum digestible
dry matter intake.
Effect of Rumen Fiber Turnover Time
Retention time or turnover time of rumen contents has been associated
with changes in both digestibility (3,46) and intake (11,39). Comparisons of
NDF and lignin turnover times in tables 2,3 and 4 provide information about
factors affecting turnover and variables influenced by changes in turnover.
Since the rate constants for passage and particle size reduction were held
constant for long hay, the turnover time of lignin, which can disappear only
by passage, is constant (45.8 hrs) . However, the turnover time of NDF fed as
long forage varies from 21.1 to 29.8 hrs. Although the turnover time of a
digestible component such as NDF represents the total effect of disappearance
from the rumen (39) it provides little insight into the mechanism affecting
disappearance because digestion, passage and particle size reduction are con-
57
TABLE 3. EFFECT OF THE PROPORTION OF THE NEUTRAL DETERGENT FIBER THAT IS
INDIGESTIBLE UPON THE DIGESTION, FIBER TURNOVER TIME, FIBER
CONTENTS OF THE DIGESTIVE TRACT AND MAXIMUM DRY MATTER INTAKE
DETERMINED BY SIMULATION
COASTAL
Variables ALFALFA BERMUDAGRASS
Indigestible fraction (% NDF^)
44.1
51.9
26.1
40.1
NDF^ Digestibility (%)
50.0
42.7
66.4
51.4
NDF^ Occurring in Rumen (%)
93.8
93.6
93.8
93.5
Dry Matter Digestibility (%)
62.7
59.3
63.0
52.5
Rumen NDF^ Content (kg)
5.24
5.79
6.14
7.87
Rumen NDF^ Turnover Time (hr)
26.9
29.8
21.1
27.0
Rumen Lignin Turnover Time (hr)
45.8
45.8
45.8
45.8
Intestinal NDF^ Content (kg)
1.22
1.39
1.23
1.77
Maximum Dry Matter Intake (% B$c)
3.02
2.74
2.58
2.01
Max. Dig. Dry Matter Intake (% BWC)
1.89
1.62
1.63
1.06
aAll values except intake were simulated
kg of forage dry matter dailv
^Neutral detergent fiber
for a
500 kg
steer i
consuming
Percentage of body weight consumed daily by a
500 kg
steer
58
TABLE 4. EFFECT OF RATE OF DIGESTION OF NEUTRAL DETERGENT FIBER UPON
THE DIGESTION, FIBER TURNOVER TIME, FIBER CONTENTS OF THE
DIGESTIVE TRACT AND MAXIMUM DRY MATTER INTAKE DETERMINED
BY SIMULATION
Variable3
NDF*3 Digestion Rate (hr--*-)
ALFALFA
.1163 .0860
COASTAL
BERMUDAGRASS
.1056 .0782
NDF^ Digestibility (%)
47.2
45.2
60.1
57.2
NDF*3 Digestion Occuring in Rumen(%)
94.2
92.9
93.6
92.2
Dry Matter Digestibility (%)
61.4
60.5
58.6
56.5
Rumen NDI^ Content (kg)
5.40
5.66
6.77
7.30
Rumen NDF*3 Turnover Time (hr)
27.8
29.1
23.1
24.9
Rumen Lignin Turnover Time (hr)
45.8
45.8
45.8
45.8
Intestinal NDF*3 Content (kg)
1.28
1.33
1.46
1.56
Maximum Dry Matter Intake (% BWC)
2.93
2.80
2.34
2.17
Max. Dig Dry Matter Intake (% BWC)
1.80
1.69
1.37
1.23
aAll values except intake were simulated for a 500 kg steer consuming
10 kg of forage dry matter daily
^Neutral detergent fiber
cpercentage of body weight consumed daily by a 500 kg steer
59
founded. Comparison of values in tables 2, 3 and 4 suggest that physical form,
indigestibility and digestion rate alter NDF turnover time.
Since the turnover of digestible materials is difficult to interpret, the
turnover of indigestible materials (such as lignin) is more useful in obtaining
insight into the mechanisms affecting digestibility and intake of forages.
However, the turnover of indigestible markers, especially lignin, probably re-
present the upper limit of turnover time for components of digesta. Data
presented in table 2 can be used to assess the effect of turnover time upon
digestion and intake since pelleting reduced lignin turnover time compared to
long forage. A 43.6% reduction in lignin turnover time yielded a 3.4 or 7.3%
decrease in digestion and 49.1 or 45.1% increase in intake for alfalfa or
Coastal bermudagrass , respectively. This resulted in an increase in maximum
digestible dry matter intake of 44.0% for alfalfa and 34.6% for Coastal
bermudagrass. Thus, a one percent decrease in turnover time results in a 0.9%
increase in maximum digestible dry matter intake.
SUMMARY
A dynamic model of fiber disappearance from the digestive tract of rumi-
nants was developed based upon acceptable and defensible concepts of fiber
digestion and passage kinetics, and coefficients obtained from available liter-
ature. The model has applicability, manageability and comparability to experi-
mental observations. Although the model can simulate the effects of some
forage and animal characteristics upon digestion, it should be realized that it
is only the initial component of an overall rumen function model. Specific
limitations of the present model include the aggregation of microbial inter-
actions with fiber and fiber characteristics into the digestion rate constants
and the assumption that fiber digestion is not limited by factors other than
fiber characteristics.
Development and use of the model suggested the need for additional infor-
mation in several aspects of ruminant digestive function. More research is
needed concerning particle size reduction, including: (1) particle size dis-
tributions in feed, digestive tract and feces; (2) changes in particle size in
the rumen associated with rumination and chewing; and (3) description of parti-
cle size reduction as a factor influencing rate of passage. Information is
also needed in describing digestion such as the effect of: (1) particle size;
(2) microbial interaction; and (3) chemical, morphological or physical plant
characteristics upon digestion rate. Additional research is also needed to ob-
tain usable rate of passage coefficients under a variety of animal states and
dietary situations.
Although improvement of the model of fiber disappearance in ruminants will
need to continue as new information is accumulated, it can be used in its pre-
sent form to assess some factors that influence forage quality. Simulation of
the model provides controlled evaluation of the beneficial effect of grinding
and pelleting forages. Analysis of plant and animal characteristics that
influence digestion and intake suggests that the proportion of the NDF in the
indigestible fraction and rate of passage influence the maximum intake of
digestible dry matter more than rate of digestion.
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I
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64
CATTLE CYCLES - RESEARCH RESPONSE
By Marvin E. Riewe
That the cattle cycle exists was confirmed again in the mid 70' s. It is
still a fact of life. The basic phenomenon has not been altered but extenuat-
ing circumstances magnified the effect of the cattle cycle on the economic well
being of the cattle producer in the 70' s.
The cattle cycle has been described as a 10-year poker game. This de-
scription seems apt. The survivors of a cattle cycle remain and get older.
One fourth of the cows in Texas in 1974 were owned by people over 65 years of
age; three fourths were owned by people over 45 years of age (5) . It seems
reasonable to assume that the recent shake out has concentrated the ownership
of cows among older people even more. Many of the losers leave the game. The
turnover rate of people in the cattle business is high. As prices improve on
the upswing in the next cycle, new players are attracted. Many people with few
cows try to play the game. To illustrate, 60% of the cow-calf producers in
Texas owned only 20% of the cows in 1974.
The question I would like to examine today is: Has the forage-beef
cattle research and extension education of the past 25 years largely fed the
idiosyncrasies of the cattle cycle rather than help producers develop a strate-
gy for coping with it?
We could dismiss the question by taking the position that science and
research is amoral. We could argue that we as research and extension workers
have no control over what the producer does. The producer decides how he uses
new technology. If he keeps too many cows, produces more calves than the
market can absorb at an acceptable price, he does so on his own initiative.
Neither research nor extension education is in anyway responsible. To argue
this position is to say, however, that our work has little influence on the
producer. Yet, our operational, tactical and strategic research (4) are spe-
cifically designed, if not explicitly stated, to do just that.
REVIEW
Let us begin by reviewing the scenario of the last cattle cycle, 1965-
1975. Beef calf production was increased from 12,412,000 head to 17,835,000
head in the 13 southern states represented here today, a 44% increase. Out-
side of the South, the remainder of the U. S. increased calf production 32%
during this same period (6) . Much of the research done by people in this group
here today made possible the feed resources that were required to sustain this
increase in calf numbers. The increase in cow numbers probably was not justi-
fied by the more limited increase in feed resources. Some of you have
questioned this too (1) .
65
Table 1. Effect of stocking rate on calf weaning weight, cow gain
on pasture and length of winter feeding, 1976-77 and
1977-78, Angleton, Texas
Stocking rate
expressed as
Ave. wean
. wt.
Cow wt.
No. days
cow-calf pair
per calf,
lbs . a
gain, grazing
winter
per acre
Steer
Heifer
season*, lbs.a
feeding
.5
600
522
236
67
.7
584
528
212
74
.9
538
483
142
110
1.2
501
475
117
114
aAll weights taken after 15-hr. overnight shrink.
t>Full feed sorghum silage (FS-1A) supplemented with urea.
*Grazing season on pasture - late March to December or January
depending on stocking rate.
When prices drop, pounds calf weaned per cow must increase to pay costs.
For example, non-pasture cost of $125 per cow annually can be paid for by 167
pounds per cow with calves selling at $75 per hundredweight. At selling price
of $50 per hundredweight, 250 pounds calf weight per cow is required and 500
pounds calf weight per cow is required with a selling price of $25 per hundred-
weight.
Research has demonstrated that weaning weights can be increased by im-
proved quality of the pasture forage including, in particular, growing a palat-
able legume in the pasture mix, systematic crossbreeding to capitalize on
hybrid vigor, use of bulls of the larger beef breeds and use of dams with po-
tential for increased milk production for the nursing calf. While definitive
weights are difficult to obtain, market weights that are available do not indi-
cate significant increases in weaning weights, industrywide, in the past 25
years. These potential gains in calf weaning weight are apparently being wiped
out by some other factor.
Increasing grazing pressure on pastures is one factor that reduces calf
weaning weights. The effect of increased stocking rate (grazing pressure) on
calf and cow gains is shown with data from a grazing study at Angleton, Texas
involving four stocking rates, each replicated three time on a common bermuda-
grass, dallisgrass, La. S-l white clover pasture fertilized with one hundred
pounds of triple superphosphate per acre annually (Table 1) . Forage availa-
bility was continuously monitored but the data is not presented here. Thus,
it seems likely that the potential for increasing weaning weights through the
use of such things as clover in pastures and crossbreeding was being wiped out
by increasing the grazing pressure on pastures.
In addition, the trend, nationally, in calving percentage was downward
(_2) as cow numbers increased. Grazing pressure was affecting the cow. Since
calf prices were improving during the upswing in the cattle cycle, a feasible
66
method of relieving some pressure on the lactating cow was to wean the calves
at an earlier age, lighter in weight. Dollar return was still acceptable to
many producers.
It is at this point that the subordination of planned research to the
idiosyncrasies of the cattle cycle are most apparent. As the effect of graz-
ing pressure exerted upon the brood cow became apparent in the late 60 ’s and
early 70' s, research was initiated in such subject matter areas as management
of light, early weaned calves (grain was cheap) and reproductive physiology.
Prices rose dramatically during the first half of 1973, and then, just as
dramatically, dropped the last half of 1973. The decline in prices continued
through 1974 into early 1975. A freeze on beef prices, an embargo on oil, and
high-price grains aggravated the situation, but these were not the causative
agents. Excessive number of cows producing calves was the cause. Now, weaning
weights were too light to spare the cow man of heavy losses.
WARNING SIGNALS
The National Cattlemen's Association has offered seven recognizable
danger signals to warn of trouble ahead in a cattle cycle (3) . Three indi-
cators come from the size of the cattle herd - (a) the annual growth rate of
the total cattle inventory exceeds 2%, (b) the annual growth rate of the cow
herd exceeds 2% and (c) the number of heifers in the current calf crop saved
for replacement exceeds 21% of the number of cows in the national herd.
Slaughter rate indicators of trouble are (a) less than 35% of the January 1
inventory are slaughtered during the year, (b) annual female slaughter as a %
of steer slaughter is less than 80%, (c) annual slaughter in numbers is less
than 80% of the previous year’s calf crop and (d) actual number of cattle
slaughtered is 2 million head per year less than that required to maintain a
stable inventory.
Historically, when three or more signals are "flashing red", some adjust-
ment is likely. Six of these signals were "flashing red" in 1952 (those who
remember will recall a major adjustment), and five were "flashing red" in 1963.
The adjustments made in the mid 1960 *s in cattle numbers and price were strain-
ing but not necessarily severe. And that apparently lulled some, even eco-
nomists, to sleep. Then again in 1972, five signals were "flashing red" and
all seven were "flashing red" in 1973.
The problem is that the warning signals start "flashing red" when prices
are high. No one wants to believe them. Perhaps this is what is meant by
"blinded by greed." On the other hand, it is difficult to fault the producer
when one reads in the Southern Cooperative Series Bulletin 186 (publication
date, March 1974) "With beef prices at the 1973 level, beef is a more profit-
able enterprise (than) in 1968 and based on projected conditions is expected
to remain in a profitable position for several years."
When the bubble burst, the cow-calf producers were weaning calves too
light. Even when the market was signaling the producer not to send any more
light calves to market, most did anyway. Many either could not or would not
wean heavier. Presumably, they could not. The seriousness of the situation is
shown in an analysis of saleable receipts June, 1975 through May, 1976 for one
67
Southeast Texas livestock market using the Packers and Stockyards Administra-
tion "model" (second week of each month) (2) . The market was clearly signal-
ing that the light calves were not wanted, yet 60% of the calves weighed under
400 pounds (Table 2). (It is assumed that only a few calves are in the 551 to
800 pound group and that these are more than offset by light cows in the 400-
550 pound group) . There has been little improvement in weight during the year
just ended, June, 1977 through May, 1978 (Table 3).
If our research is not to be subordinate to the peculiarities of the
cattle cycle, then the priority for our research and extension education effort
would seem to be to provide the Southern producer the technology that allows
him to develop a system of management for marketing heavy calves; say, a mini-
mum of 550 to 600 pounds. This is necessary to reduce risks to producers
incurred during the liquidation phase of the cattle cycle. To reduce the risks
associated with the liquidation phase means that producers will resist certain
temptations to maximize profits during periods of peak prices and excessive
risk.
PROBLEMS TO OVERCOME
As people involved in forage-beef cattle research and extension educa-
tion, we have some in-house problems to overcome to make our efforts more use-
ful to the producer.
First, we must understand the industry and the producers we serve. The
technology we develop must be acceptable to the user. If in the user's view,
he must incur considerable risk in adopting the new technology, he will likely
not adopt it. "True risk", given adequate data, can be estimated. But, "true
risk", as far as the producer is concerned, does not count. Rather it is the
risk as the user of technology perceives it that matters. One function of
extension education might be to reconcile the producer’s perceived risk with
"true risk."
Having said this, I am left with a paradox. It seems difficult to re-
concile the apparent willingness of many producers to accept the excessive risk
associated with increasing numbers and yet not accept the lesser risk associ-
ated with managing the cow herd and pasture in a manner necessary for heavier
weaning weights and reduced losses in the liquidation phase of the cycle.
Perhaps it is that for most producers, probably 90% or more, cattle are not a
primary source of income. Perhaps, the cattle business, for many producers, is
even more like a poker game than we care to admit.
A second problem is false notions we harbor that increasing the carrying
capacity of a pasture is of itself a worthy goal and that maximizing live-
weight gain per acre also maximizes profit per acre. The non-pasture costs of
maintaining an animal are paid for by production or gain per animal. In this,
production or liveweight gain per acre does not count. We must become more
sophisticated in our economics. This kind of thinking does indeed subordinate
our work to the eccentricities of the cattle cycle. Risks in the cattle cycle
are reduced by paying strict attention to the production or gain per animal
with the view of getting the job done with the fewest animals possible. Get-
ing the job done is balancing the risks involved with appropiate opportunities
for profit.
68
Table 2. Composition of saleable receipts at one Southeast
livestock market, June, 1975 through May, 1976
Texas
Class, weight-
■lbs
•
Sample
Number Percent
Average
$/cwt
Baby calves,
150
&
less
479
1.5
17.15
Calves ,
151
-
250
2,713
8.4
20.45
Calves ,
251
-
400
12,404
38.3
24.25
Cows /Calves ,
401
-
550
8,847
27.3
27.61
Cows /Calves ,
551
-
800
4,534
14.0
22.29
Cows ,
801
&
up
3,175
9.8
21.11
Cow-calf pairs
70
.2
22.96
Bulls
176
.5
26.43
Total in sample
32,398
100.0
25.12
Table 3. Composition of saleable receipts at one Southeast
livestock market, June, 1977 through May, 1978
Texas
Sample
Average
Class, weight-
■lbs
•
Number
Percent
$/cwt
Baby calves.
150
&
less
233
.7
25.57
Calves ,
151
-
250
2,143
6.7
40.16
Calves ,
251
-
400
11,065
34.7
38.71
Cows /Calves ,
401
-
550
8,793
27.6
37.73
Cows /Calves ,
551
-
800
5,305
16.6
29.86
Cows ,
801
&
up
3,984
12.5
26.92
Cow-calf pairs
89
.3
36.06
Bulls
268
.9
33.97
Total in sample
31,880
100.0
33.63
Another notion needs to be re-examined. "Minimal cost of beef comes from
a 1,000 pound animal. In order to market the calf, then we must carry the calf
on to about 1,000 pounds slaughter weight." I am aware of the classical
studies which show that with the calf continuing to grow at a creditable rate
and taking into account the maintenance requirement of the cow, the energy
required to produce a pound of beef is minimal at slaughter weights of about
1,000 pounds. The problem is that the source of the energy is not taken into
account. With the feed resources commonly available in the South, we can,
without great difficulty, wean calves weighing in excess of 500 pounds.
Programs heavily dependent upon warm season perennial grasses grown with a
compatible clover have been designed which will produce calves weaning at
weights of 600 pounds or heavier. Yet calves grazing these same pastures post-
69
weaning will not gain at a generally acceptable level unless they first endure;
a period of undemutrition to provide opportunity for compensatory growth. We
need to examine the question of what is an optimal slaughter weight given the
resources we have available, or are likely to have available, in the South.
A third problem of some concern is parochialism. By parochialism, I
mean aspiring to develop production programs where we do not and likely will
not have a competitive advantage. To illustrate, we are not likely to produce
Choice grade slaughter beef- in large numbers in the South unless Southwestern
and Midwestern feeders first fail because of high grain prices. To attempt to
capitalize on their failure would still leave us vulnerable with respect to
competing for such inputs as nitrogen fertilizer. We would be much less
vulnerable if we develop those areas where we have a competitive advantage
such as cow-calf programs and then extend this to the production of slaughter
animals grading less than Choice or Good.
RESEARCH NEEDED
What kind of research and extension education effort is required to
develop strategy for coping with cattle cycles? Cow-calf programs are funda-
mental to the beef cattle industry in the South. Heavier weaning weights are
extremely important in providing some degree of economic stability for our
producers. This, then, suggests the following areas of priority research and
extension education efforts.
A major effort is required to extend the use of palatable legumes in
Southern pastures. The question regarding the need for legumes in Southern
pastures should be resolved in most minds by now. Legume yield and persistence
in pastures should be increased. Learning to effectively manage and utilize
legumes in pastures is paramount.
The improvement of quality of warm season perennial grasses through
breeding and/or management without sacrificing ease of establishment, per-
sistence, cold tolerance, disease and drouth resistance is priority research.
Increasing the genetic potential for gain in the Southern cow herd is a
prerequisite to coping with the cattle cycle. Research and extension education
in this area must continue.
Each of you, I am sure, can suggest other areas of priority research.
The point is that those things that make it possible to have more cattle with-
out improving production or gain per animal tend to feed the idiosyncrasies
of the cattle cycle. On the other hand, those things that improve production
or gain per animal allow for development of a strategy for coping with the
cattle cycle.
To have a stable beef cattle industry in the South, our producers must
achieve economic maturity. The charge to research and extension education is
to help our producers reach that maturity.
70
LITERATURE CITED
1. Taylor, T. H. and W. C. Templeton, Jr. 1971. Legumes in perennial cool-
season grass sods. Proc. 28th Southern Pasture and Forage Crop Improve-
ment Conference, Stillwater, Oklahoma.
2. Sartwelle, J. D. 1978. Personal communication.
3. Welch, John. 1978. Early warning signals - To help you cope with the
cattle cycle. Mimeographed Paper. Texas Animal Agriculture Conference.
4. Wortman, Sterling. 1976. The world food situation: a new initiative.
Rockefeller Foundation Working Paper.
5. U. S. Bureau of Census. 1977. Census of Agriculture, 1974. Vol. 1,
Part 43, U. S. Dept, of Commerce, Washington.
6. U.S.D.A. 1972-77. Western Livestock Roundup. Monthly issues for 1972-77.
71
GRAZING SUBTROPICAL PASTURES - COMPONENTS AND SYSTEMS
By Elver M. Hodges
One of the first sources of improved pasture in south-central Florida
was common bermudagrass that grew in garden and farm areas in response to
cultivation and increased fertility. Planned development of better grazing
for cattle centered around carpetgrass and common bahiagrass. Low input and
low productivity values were associated with both varieties. Improved pasture
fertilization for the 1940 decade consisted of 500 pounds per acre of 6-6-6,
once annually, with a ton of dolomitic or calcic limestone added on a once-in-
severa 1-years basis. The latter half of the 1940's saw extensive plantings
of Pangola digitgrass and Pensacola bahiagrass along with increases in
fertilization rates. Legumes on the flatwoods lands were limited to white
clover, Hubam sweet clover, and a little black medic; some alyceclover was
grown on soils with better drainage and higher fertility. These cool-season
legumes were erratic in production but yielded dramatic increases in cattle
gain per acre when all factors were favorable. It was demonstrated in the
early 1950's that irrigation could be used to make white clover a reasonably
reliable crop when managed intensively. Yield relationships between ordinary
grass pastures and a highly successful clover-grass pasture ranged from less
than 100 pounds per acre on carpetgrass and 300 pounds on Pangola to 800 pounds
on irrigated white clover-grass. The need for consistent, high level manage-
ment plus the water requirement placed a continuing limit on the acreage of
white clover. During the era of moderate fertilizer costs it was observed
that Pangola digitgrass responded strongly to increased rates of fertilization.
Nitrogen levels of 100, 200 and 300 pounds per acre annually, applied in split
applications, produced warm season per acre animal gains of 300, 468, and 568
pounds respectively.
Annual ryegrass (Lolium multiflorum) has been planted in lawns in
peninsular Florida for many years. Its value for pasture was limited by rust
damage, low soil fertility and dry weather. The development of rust-resistant
varieties and a better understanding of plant food needs made ryegrass a useful
possibility for winter and spring grazing. Sorghum-sudan hybrid forages have
had value on better drained areas but ordinary flatwoods sites are too
susceptible to extremes of drought and wetness.
Two annual warm season legumes. Hairy indigo (Indigo fera hirsuta) and
Aeschynomene (Aeschynomene americana) , became available during the 1950 's and
were grown in combination with various perennial grasses. Hairy indigo proved
to be less palatable than Aeschynomene and more emphasis has been placed on
the latter variety.
72
'
TABLE
1 . --Hay consumption, weaning rate and weight, and calf production per
acre on eight forage and supplement systems. ARC, Ona, 5 years!/
Hay
Weaning
Weaning
Calf
System
per cow
rate
weight
production
lbs. annual
7,
lbs.
lbs/acre
Grass
485
67
481
213
Grass
+ molasses
331
77
483
244
Grass
4- Hubam
706
68
467
213
Grass
+ Aeschynomene A
573
82
474
224
Grass
+ Aeschynomene B
639
75
434
205
Grass
+ whi tec lover
529
69
483
221
Grass
+ ryegrass
154
72
507
218
Grass
+ ryegrass + sorghum
154
82
501
255
+ whi tec lover
1 J E. M. Hodges, F. M. Peacock, H. L. Chapman, Jr., and R. E. L. Greene.
1974. Forage and supplement systems for beef cows in south-central
Florida. Proc. Soil & Crop Sci. Soc. of Fla. 33:pp 56-59.
TABLE 2. --Hay supplement, weaning percentages, weaning weight, and weaned calf
production on four forage systems at ARC, Ona , 1973-1976 —
Forage
System
Supplements 1
hay per
cow, annual
Weaning
ra te
Weaning
weight
Calf
production
lbs.
%
lbs .
lbs/ acre
1. Grass
315
80
481
237
2. Grass + extra N
185
88
505
278
3. Grass + ryegrass
423
80
505
252
4. Grass + ryegrass
362
88
503
273
+ clover
1/ E. M. Hodges, F. M. Peacock, H. L. Chapman, Jr., and D. Crane. 1978.
Forage systems for cow-calf herds in south-central Florida. Proc.
Soil & Crop Sci. Soc. of Fla. in press.
73
A series of mini- forage systems were established at ARC, Ona , beginning
in 1967 and weaning percentage, weaning weight, and calf data from this
experiment appear in Table 1. Seven systems were established with breeding
herds of 25 cows on 40-acre units and continued year-long. One unit, consis-
ting of perennial grass supplemented with molasses, was stocked with 30 cows
on 40 acres. The perennial grass was fertilized twice annually with 50-25-25
pounds per acre of N, P2O5, K2O. The legumes received no nitrogen and ryegrass
received additional N as conditions indicated. The molasses-supplemented
perennial grass and the ryegrass-clover-sorghum systems produced the most calf
poundage per-acre. Calf weaning weights were excellent on all treatments.
A second trial, covering four years, was established with four treatments,
each of which included 50 breeding-age females. It was observed in the first
system series that N was constantly in short supply and, accordingly, the base
rate was adjusted to include two annual applications of 64 pounds/acre N in
the second experiment. In addition, one treatment received 50% more N annually
in a third application which was spaced between the early spring and the fall
dates. The annual legumes were omitted from the second trial, not for lack of
value but because of the limit on variables that could be handled.
The herds in the second experiment received only limited amounts of hay
in some years. Data in Table 2 show weaning rates ranging from 80 to 88
percent with no statistically significant difference. These values represent
a range substantially higher than in the preceeding trial. Weaning weights
were similar for all treatments and only slightly higher than those observed
in the first trial. Production per-acre on the basic grass system was 11
percent above the earlier value, 237 pounds vs 213 pounds while the nitrogen-
fertilization rate was 28 percent higher in the second trial.
The similarity of results between systems indicates that orderly manage-
ment can combine a number of different components into workable herd production
systems. It has been a continuing observation that the intensive grazing
systems require a reserve of stored forage to allow adjustment to wide fluc-
tuations in weather and the consequent changes in forage supply.
74
LOOKING TO THE FUTURE IN FORAGE-ANIMAL PRODUCTION
by R. E. Blaser
Concerning this topic, it is precluded that the paper should deal with the
animal-forage complex. However, the future progress depends on professional-
ism in research, teaching, and service. In the broadest sense, we profession-
als are charged with responsibilities for developing and implementing princi-
ples to manage the soil-biotic-climatic complex so farmers may encounter less
risk and potentially more profit from ruminants. Consumers would also benefit.
I begin with praise for our many excellent accomplishments in a wide array
of interplaying factors to advance ruminant production. A long list of varied
citations would be very impressive, commendable, but incomplete. However, when
compiling all costs for professional, technical, and semi-technical personnel,
operations, etc. as compared to our accomplishments as individual professionals
we would likely be either depressed or surprised. Have we professionals
achieved high potentials of service and knowledge to advance forage and rum-
inant production?
We dislike evaluation, don’t we? Each one of us should be required to
evaluate our individual accomplishments yearly, writing out what new principles
have been established that have advanced knowledge or been implemented into
practice. Listing the accomplishments during the past five years and projected
programs for the next five years could concurrently point out weaknesses and
strengths and serve to stimulate new creativity and innovations for progress
along with the joy of serving in our professions to benefit mankind through
research, teaching, and service. A strong, continued, and dynamic professional
growth to improve knowledge and services should be our mission.
At our university, promotions and salary increases depend on annual eval-
uations - assistant professors may draw higher salaries than professors. The
drawing of large salary increases by proficient faculty and no increases by
"nonperformers" is endorsed. After being asked how to develop a strong Insti-
tute of Research in Chile by Director Ellguetta, I suggested that salaries not
be paid on the basis of age, sex, color, family name, degree, but on the basis
of accomplishments substantiated by annual self-evaluations by each profession-
al. After adopting this recommendation, Mr. Ellguetta was pleased to report
that self-evaluations stimulated new innovations and improved the amount and
quality of research by more than 30%.
We often "rehash" old work or pursue research where the results can be
predicted. Many projects will have little impact on the livestock industry.
Paper presentations often give little new information. The free and fixed so-
called "hard" state and federal funds are assigned irrespective of accom-
plishments. Funding for salary, rank, and operations should be based on the
effectiveness of our professional contributions, be they research, teaching,
extension, or business pursuits. Would this stimulate creativity and perfor-
mance? Some professionals have become "freeloaders" at state and federal
levels .
75
Unless evaluations of professionals are sharpened, there will be a con-
tinued decline in proficiency and this is partly responsible for inflation and
other problems in our society. In contrast, the so-called "soft" contract
funds for research, teaching, and extension are in reality "hard" monies.
Such funds awarded to innovative projects must be justified by meaningful inter-
pretations of findings and recommendations for implementation.
In my opinion, protectionisms such as tenure and state and federal person-
nel acts, unions, and civil service concepts have promoted or tolerated medio-
crity. Socialization is a serious deterrent to professional growth and ser-
vice. To fulfill a pledge of reorganizing federal bureaucracies for efficiency,
President Carter began by making all positions secure. Socialization contin-
ues with the federal law that allows persons to work until they are 70. We
oldsters should be replaced by qualified young persons.
Lowering the standards for student enrollment and for professionals to
accommodate minority groups is of grave concern. Historically and generally,
the advancements in the United States in medicine, agriculture, industry, and
other arenas have been directly associated with excellence in professionalism.
Supporting roles are very important; thus, individuals with sub-professional
qualifications, regardless of race, sex, or creed, can perform very useful
services in such areas. Indeed, persons not qualified for the high standards
of professionalism will undoubtedly be more contented and mentally stable in
supporting roles.
It is noteworthy that there is little criticism about fairness in pro-
fessionalism in male athletic programs. For example, the winning basketball
teams at many institutions are allied with the excellent black professionals.
No one is complaining when all persons on an athletic team are black, unless
they lose. Competency should be of highest priority from the viewpoint of
new innovations for continued advancements in society. Professional qualifi-
cations are not saddled with sex, race, or creed. Talents differ; we must
recognize that supporting and leadership roles are always components of
societies. Service, concern, and love should be interplaying ingredients
among persons, all areas of employment being important.
Although it has not been true in the past, I believe the doors are now
open for qualified professionals in any arena. Concerning women, we welcome
them as co-professionals. About 1/3 of the students in my senior and grad-
uate course in forage ecology and utilization are females, many being top "A"
students and highly qualified persons.
At all levels, creativity, originality, and quality and quantity of out-
put by professionals is often impaired by "overadministration" which depresses
funds and productivity because of useless paperwork. Administrative confusion
is of concern in many federal areas and entanglements in state and federally
administrative programs often discourage professionalism. Strong extension
specialists should be employed with freedom to do their "thing"; instead, the
top and sub-sub-lines of administrators inhibit the quality of professionalism
and progress by regimentation of programs. Will administrative arenas be re-
duced and simplified and a "professional trust" be reestablished?
RUMINANTS AND FORAGES
Ruminants of paramount economic importance since biblical times will con-
tinue to make formidible, economic contributions for food and clothing. As hu-
man populations increase, the best tillible soils will have first priority for
76
producing legume and grain cereals for direct human consumption. The nutri-
tional aspects of cereals will be improved genetically or further fortified to
satisfy the needs of human nutrition and health. However, rolling topographies
make it necessary to use perennial grass-legume associations alone or in rota-
tions to maintain or improve soil structure and organic matter, all serving to
increase water infiltration to reduce erosion and improve fertility. Pending
on costs of nitrogen and crop pest control, perennial grasses and legumes may
again be used in rotations. Marginal stony and shallow soils will be used
exclusively for forages. Ruminants will be used extensively for converting
crop residues and animal wastes to food and other products. Financial or
cyclic risks among cattle producers and a poprly informed public are serious
unsolved problems.
Ruminant Efficiency
Unfortunately, there is little specific information on the possibilities
of developing races of ruminants that are efficient converters of forages to
animal products. Letter queries seeking data on this topic have generally
been tabled. The general opinion from replies state that ruminants with the
highest feed conversion from grain-forage rations are also most efficient for-
age converters. Large "growthy" ruminants are generally superior to smaller
compact types. Breeders and geneticists see little chance for improving the
efficiency on forage diets since the lifetime diet of beef cattle is generally
70-80% forage. Unfortunately, registered and unregistered young bulls in test-
ing programs are invariably fed high grain rations to measure genetic poten-
tials and to promote sales.
With female cattle replacements, a reasonable goal is to select replace-
ments restricted to forages, excluding corn silage. At Middleburg, females
not fed grain since 1951 have averaged over a 90% weaned calf crop on herba-
ceous forages. Cows without a calf during any year go to the butcher. Longe-
vity and productivity of our cows have been excellent, 12 calves during the
life span being common. As compared to other herds, we do not know whether the
Middleburg herd is more or less efficient on herbaceous forage diets. Appar-
ently, buffalo and buffalo crosses have forage conversion rates similar to
those of cattle. Apparently, there is no breed or type best for all condi-
tions (_8) . The possibility of developing special cattle races highly efficient
in converting forages is an important unanswered question and apparently of no
immediate concern to animal breeders. Can intake of forage and digestibility
in the rumen be augmented? Such high risk research should be investigated as
an increase of 1 percentage unit in ingested digestible energy (IDE) of any
forage would be of national and international importance for increasing pro-
duction efficiency.
PROBLEMS AND NEEDS
We have prepared 5 review interpretations (JL, 2_, _3, 4 , and 5) with many
references dealing with principles and philosophies for managing animal-forage
systems. Thus, statements herein are not substantiated by references and I
will discuss only a few of many factors dealing with ruminants in grazing
regimes.
Insufficient ingested digestible energy (IDE) by ruminants from the sum-
mer growth of most perennial forages deters economic production of ruminants
with high energy requirements. The efficiency of energy conversion from
77
forages for growing or finishing meat producing animals and lactating cows
increases sharply as IDE is elevated. Supplementary grain feeding (energy)
with herbaceous forages invariably increases rates of gain or milk production,
but may or may not be economical. The need of supplementing energy to her-
baceous forages depends on species, season, stage of growth, grazing pressure,
and the ruminant category. Silages of grain varieties of corn and sorghum need
not be supplemented with IDE. Conversion efficiencies of such silages are
high, daily gains exceed 2 pounds and choice carcasses are commonly produced.
Ingested digestible protein, even for high producing lactating cows, is
usually adequate with good management of temperate annual and perennial grasses
and legumes.
The need for high yields, longevity, and high IDE of temperate grasses
and legumes is critical. Because of new diseases and insects, the new varie-
ties are superior but have generally maintained yield levels of varieties of
several decades ago when some of the present pests were absent. The IDE val-
ues, under controlled management for old and new varieties of temperate spe-
cies, are similar. There have been marked increases in IDE and yields of some
semitropical forages.
Because of pest problems, the acreages of alfalfa in the South have
declined and yields stagnated. A decade ago, some plant breeders under the
auspices of industry indicated an early availability of high yielding hybrid
alfalfas. Where are such hybrids? Working with temperate perennials embodies
"tough" genetic problems requiring the best in new innovations. Natural selec-
tion processes have produced good varieties of tall fescue, orchardgrass ,
timothy, bromegrass, red clover, alfalfa, bluegrass, and perennial ryegrass.
Hopefully, some of the turf type bluegrass and ryegrass varieties might be used
in forage systems. As long as 10 years of research to isolate superior varie-
ties of different species have often failed. To obtain superior varieties, it
might have been more innovative and productive to seed potentially adapted spe-
cies on many farms in different environments under judicious grazing. During
10 years, this would have resulted in rigorous natural selection for disease
tolerance and other adaptive factors from multimillion populations and multi-
environments. Alfalfa varieties were seeded on a given soil (6J) : a) where
alfalfa had never been grown; and, b) immediately after alfalfa. Yields are
substantially higher on the "new" land, many varieties being extinct where
alfalfa followed alfalfa. This indicates that plant breeding should be con-
ducted on "dirty" land to obtain disease and insect resistance. Germplasm from
temperate forages should be sought with enthusiasm from various "old" field
environments. This is not sophisticated, so it will likely not be pursued,
even though nature has been more successful in developing turf and forage
varieties than some plant breeders.
Perennial ryegrass in mixtures is the key to successful grassland farming
in many countries with temperate environments. It was accepted that perennial
ryegrasses were not adapted to humid, eastern USA. Bluegrass has been con-
demned, disced, burned, killed with herbicides, and replaced by taller grasses
and clover. Yet, in the mid-Atlantic region, bluegrass-clover mixtures produce
animal gains and products similar to those for tall grass-clover associations.
Turf agronomists have found persistent bluegrass and ryegrass strains in
"nature". Are there forage types of these two and other species in nature
waiting to be made useful? Farmers need better bluegrasses, perennial rye-
grasses, and reseeding annual ryegrasses to plug into forage systems for rum-
inants having high IDE requirements and for lengthening the grazing seasons.
Alfalfa with rhizomatous or proliferating roots are needed for 12-month
78
forage systems. Such morphological types would invade and regenerate stands
after mismanagement or pest epidemics. Also, morphological branching roots
would make alfalfa adapted to semi-poorly aerated soils.
In forage management and physiology, there are serious shortcomings. We
need to investigate species and genotypes under flexible managements to lengt-
hen grazing seasons, improve mid-season production in year-round grazing pro-
grames with minimum harvesting. New work indicates that alfalfa and red clo-
ver may be grazed during early spring and stockpiled with grasses for winter
grazing, in functional systems. For spring seedlings, autumn simulated graz-
ing of red clover has not depressed stands nor dry matter yields. Tall fescue,
thought to be too aggressive for alfalfa, appears promising, but in new seed-
ings, alfalfa subdues fescue. We have obtained 2 tons of stockpiled tall fes-
cue during late August-November from nitrogen transfer from alfalfa.
Tall fescue is a fantastic plant, broadly adapted, suitable for flexible
management and uses - turf, erosion control, and in forage systems. Highly
rhizomatous genotypes with high fructosan contents and yield potentials that
maintain chlorophyll and cell structure for photosynthesis and retention of
soluble carbohydrates and proteins during low winter temperatures are needed.
As cells rupture during winter, fructosans (nearly 100% digestible) leach,
causing declines in digestibility from around 70% in November to 45% in March.
Simultaneously, it is very important to develop tall fescue free of toxicity
syndrome (s) that will also improve IDE during summer. Steers grazing N fer-
tilized Ky 31 fescue during the spring-fall season averaged 0.91 lbs daily as
compared with 1.70 lbs during the autumn-winter season.
Declines in daily gains during the summer season with controlled grazing
pressures occur with temperate and semitropical species. Can legumes, man-
agement, other species, or varieties arrest such declines in animal production?
The best IDE and outputs per ruminant from herbaceous species in the
Southern region occurs during the late autumn-early spring season from winter
annual grasses and legumes and possibly tall fescue. Can the risk of poor
growth and seasonal distribution be subdued?
In the southern region, the maintenance of legumes is a serious economic
problem. There has been excellent legume renovation research; however, better
economic methods of regenerating and maintaining legumes in temperate grasses
and establishing winter growing grasses and legumes in semi-trapical grasses
are needed for forage systems. Can we find red and ladino clover varieties
and managements for natural reseeding and regenerating as with white clover?
Is it possible to maintain temperate perennials or volunteer winter annuals
and semitripical species in association for year-round grazing?
COOPERATION
Concerning the forage-ruminant complex, cooperation has often been deter-
red by departmentalization. Strong departments with highly qualified profess-
ional personnel are essential. However, departmentalization is not functional
in nature. Natural or artificial soil-biotic-climatic complexes demand multi-
disciplinary analyses and action programs for economic ruminant enterprises.
As professionals in different departments, we should cooperate and direct our
efforts to advance ruminant production in various environments. Thirty years
ago, in Virginia, a written cooperative dairy-agronomy grazing project with
milk cows stated that the agronomy department would furnish the Ky 31 fescue
seed. It is different today. However, there is often only superficial co-
operation; personnel in few states and federal organizations have
79
model cooperative team research among professionals to serve the broad complex
for economic production of ruminants. Cooperation for enjoyable progressive
programs cannot be made functional with an "administrative hammer". However,
administrators should employ professionals with vision and cooperative apti-
tudes .
Can we listen and hear each other in developing relevant research in the
broad arena of ruminant production unselfishly? Not yet! In environments of
professional diversity, where ruminants are departmentalized, do we invite
cooperating scientists to discuss and debate vigorously and openly? I am con-
vinced that advancements in ruminant production depend on wholesome cooperation
among scientists in various disciplines. Farmers want ideas, the departmental
source is not important. However, cooperation will not assure relevance in
research or extension; dynamic creativity, idea sharing, and free debate among
each professional is essential. Progress and quality depend on ideas. In
cooperative endeavors with complex systems, full agreement among the diverse
scientists should not be anticipated nor required.
VISION, SYSTEMS, AND PHILOSOPHY
To speed up economic advancement of ruminant production, extension and
industrial personnel should assemble known principles into forage-animal man-
agement systems of production for economic evaluation. Many known principles
are not being implemented by extension and industrial personnel. Many farmers
will cooperate and such results should be published. This may serve as an im-
petus for researchers to develop forage- ruminant systems. Developing systems
and obtaining new information is not a research responsibility per se. Ideally
a team of persons in research, extension, and industry might plan forage-animal
management systems for economic evaluation on farms. For example, an extension
consultant, Jorge Zubizarreta in Argentina, has implemented principles from
our work into systems of many large farms. When calling at my office and
referring to Research Bulletin 45 to discuss principles, he closed the booklet
stating, "No, I know what's in there and we use it - what have you that’s new
that can be incorporated into forage-animal systems?" Farmers he advises are
using the principles of creep feeding, creep grazing, and first and last
grazing in management systems.
At a session of this group about 18 years ago, Brady Anthony referred to
a publication (7) which stated that 4 month old calves restricted to the dam’s
milk gained .33 lbs as compared to 2 lbs when calves had milk and feed. This
important factor to be plugged into systems has generally been ignored. Why
have animal scientists generally not accepted or disproved this very important
principle? But listen to a paragraph in a letter from Anthony,
"I have made rather extensive calculations on the milk produc-
tion of beef cows relative to calf performance. Our data show that
the nursed beef calf must receive an outside source of nutrients
equal to its caloric intake for milk at 90 days of age if it is
to continue to grow at a rate of approximately 1.7-2 lbs daily.
After 90 days of age for the rapidly growing calf, the percentage
of its daily feed supply from milk rapidly declines. This situation
holds for all beef cows nursing calves. This means that after the
calf is 90 days of age, its performance is primarily conditioned by
the source of food other than milk."
80
We would be critical of published concepts and statements in the forage-
animal complex. It is easy to be wrong in this complex enterprise. Defying
that weaning weights of calves depend on the dam's milk supply and the bull
has opened new horizons. Defying that silage must be at least 65% moisture
and making 40 to 50% dry matter silage has led to high quality energy silages
from com and grain sorghum. Such energy silages with only urea-protein meal
supplements are forage-animal systems for weaned calves, fattening and lac-
tating cows. Beef cows do not deserve such energy forages. Many texts still
refer to all silages as roughages.
Fixed and Managed Experiments
Persons in departments with responsibilities and concerns to improve
ruminant production should pursue objectives in the following areas:
1) Plant Phases, Ruminants Not Needed as Testers: Dedicated efforts to
develop simple forage systems for various environemnts for year-round grazing
and minimum harvesting that provide the nutritional needs for different classes
of ruminants and cycles of production economically.
2) Ruminant Phases: To develop desirable ruminants for various environ-
ments (long-lived, high levels of health and reproduction, disease and pest
resistance, efficient in forage conversion, desirable marketing qualities)
through genetics and a broad spectrum of ecological sciences or factors.
3) Animal-Plant Phases: To develop and evaluate simple and economic
ruminant-forage management systems for various environments for entire cate-
gories of production such as calf production through weaning, growing phase,
fattening or milk production. The systems with beef cattle should embody
year-round grazing with a minimum of harvesting, mechanization, and hand
feeding.
These research areas provide opportunities for personal professional
development through individual, intra-departmental or interdepartmental
research. The missions are to obtain relevant findings to be plugged into ani-
mal-forage management (phase 3). Assembling factors and managing them in sys-
tems to establish principles and economic potentials on farms has generally
been ignored. Farmers hunger for such operational packages.
The research philosophy for these phases embodies two categories: a)
classical designs with fixed variables; and, b) managed variables. The
classical experiments with fixed variables are relatively simple to conduct.
They are said to be objective because judgement is excluded during the conduct
of the experiment. The findings are usually narrow in scope, pertaining to
fragments of the broad complex of ruminant production. Such experiments are
replicated, analyzed statistically giving probabilities, and published in
elite peer review journals. Many experiments in this category are useful, but
discussions to advance knowledge and implementation are usually weak.
Designing experiments with managed variables requires dynamic judgement
while experiments are in progress. Since judgement is exercised, managed
experiments are said to be subjective, unreliable, biased. A farmer is a
manager; he makes decisions daily on wise compromises for producing desirable
products profitably. When pocketed dollars increase because of management, is
this objective? The point is that most of us can be complacent; we are not
stressed or possibly we are not as well versed as a good farmer. We tend to
abhor management in experiments. Listen to three Georgians. McCormick, Hale
and Southwell (9) were disappointed with fixed objectives when fattening steers
on small grains. Listem to them, "The conditions followed in conducting the
81
3 phases of this study were necessarily fixed; whereas, commercial feeders may
adjust operations and ultimately realize more profits." Wisely, they pointed
out weaknesses in their data and elaborated on managements that farmers might
have used. Note this was published in a bulletin, not in an elite journal.
The writing of a strong bulletin showing how to implement findings into farm
practices requires highly versatile and knowledgeable professionals. One rel-
evant publication in this area may be equivalent to several publications in
elite journals with fragmented data. If you believe this, tell your dean and
peers, - I have.
McMeekan researched fat lamb and milk production in New Zealand. Liter-
ature reviews credit him with evaluating rotational with continuous grazing
under constant stocking rates. McMeekan actually imposed managements to
vary the nutrition needed for classes of ruminants for various cycles of pro-
duction through pasture management. Stocking rates for rotational and con-
tinuous grazing were constant but varied within each to allocate the needed
nutrition. He did not compare rotational versus continuous grazing per se -
he imposed harvesting and management. Further, in "control grazing", he did
not use a given number of days grazing and resting within a paddock. Cows
were shifted from a rotationally grazed pasture when judged that IDE became
inadequate for lactation. McMeekan also stressed ruminants during certain
reproductive cycles rather than pastures. Thus, McMeekan' s subjective
(managed) experiments were highly objective, based on their worldwide in-
fluence on economic production of ruminants.
In year-round forage-ruminant systems to produce ruminant products profit-
ably, management is important. At Middleburg, experiments with forage-cow-
calf systems investigated raising beef calves through weaning. Given cows
were restricted to each of 10 systems for 4 years. The production goals of
weaning calves at 550 lbs, a 90% calf crop, and high calf production/A were
realized. Two reasonably high stocking rates with year-round grazing for sev-
eral systems were compared with grazing-hay feeding systems. For simplicity,
there were only 3 fields in a system. Each system was managed independently
to realize the highest and practical potential of the systems.
Grazing pressures ranging from low to high at a given moment mean ranges
of high to low nutrition (energy and protein intake) . The continuously high
nutrition requirements of calves were maintained by opening gaps to a fresh
pasture (creep grazing) whenever grazing pressures of pastures grazed by
cows and calves become high. When the residual pastures grazed by cows become
extremely short (very heavy grazing pressure and plant stress) , the cows were
shifted in with the calves cn the creep grazed pasture. The cows and calves
then grazed together until judgement (management) indicated that the grazing
pressure again deterred calf growth. At this point, the creep grazing gap in
the next fresh pasture was opened, cows again grazed the residue, etc. This
alternate creep grazing and no creep grazing is managed to maintain low graz-
ing pressures for calves to achieve high growth rates and weaning weight goals.
Conversely, grazing pressures of cows vary sharply - a medium grazing pressure
during a few weeks before c alving until calves are 3 or 4 months old to provide
milk and to stimulate estrus for early conception. Such grazing pressure-nu-
tritional control for allocating quality forage to calves instead of cows is
economic, allowing high stocking to increase calf gains/A without sacrificing
gains/ calf.
Creep grazing or creep feeding is of no value under low stocking-low gra-
zing pressure regimes unless forage is of poor quality. The Alabama findings
show better calf gains from bermudagrass-clover mixtures than from bermuda-
82
grass; the differences were not attributed to milk production. Calves, about
3 months old, require quality forage or grain along with milk from their dams
for high IDE.
With managed forage systems, cattle can be finished to good and choice
grades without grain; likewise, beef cows, ewes, Stockers, and replacements
do not need grain nor protein supplements with managed forage systems.
When evaluating varieties, it is often recommended to use 3 stocking
rates and several replications. Management in such experiments can save
space, time, and money. For example, when ascertaining milk production po-
tentials from Ky 31 versus Kenwell fescue or liveweight gains from Ky 31
versus Kenhy tall fescue, one controlled (managed) grazing pressure was ade-
quate for evaluation and to show severe fescue foot of cattle grazing Kenwell
and Kenhy varieties at Middleburg.
Usually, in research and service, farmers get fragments of information.
We need to help them by planning forage-ruminant management systems for en-
tire economic phases of ruminant production. Managing the interplaying fac-
tors and controlling and allocating IDE to appropriate ruminants has tre-
mendous economic potentials. Managements should be planned to recycle
animal excreta to increase forage yields. Also, cows during certain stages
of reproduction may be used to replace "machines" as for grazing rather than
mowing weeds, and very high grazing pressures to reduce grass competition when
reestablishing legumes.
83
REFERENCES
1. Blaser, R. E. , D. D. Wolf, and H. T. Bryant. 1973. Systems of grazing
management. Forages , The Science of Grassland Agriculture. The Iowa
State University Press.
2. Blaser, R. E. , H. T. Bryant, and R. C. Hammes, Jr. 1969. Managing forages
for animal production VPI & SU Res. Div. Bulletin number 45.
3. Blaser, R. E. , R. C. Hammes, Jr., J. P. Fontenot, C. E. Polan, H. T. Bryant,
and D. D. Wolf. 1976. Forage-animal production systems on hill land
in the Eastern United States. International Hill Land Symposium. In
pres .
4. Blaser, R. E. , E. Jahn, and R. C. Hammes, Jr. 1976. Evaluation of forage
and animal research. Systems analysis in forage crop production and
utilization. Crop Science Society of America. Special publication
number 6.
5. Blaser, R. E., W. C. Stringer, E. B. Rayburn, J. P. Fontenot, R. C. Hammes,
Jr. , and H. T. Bryant. 1977. Increasing digestibility and intake
through management of grazing systems. Forage-Fed Beef: Production
and Marketing in the South. Symposium. Bulletin 220, Southern Coop-
erative Series.
6. Blaser, R. E. 1977. Forage systems for fattening steers with a minimum
of grain feeding — new grazing research. Northern Virginia Forage
Conference. March 10.
7. Hammes, R. C. , Jr., R. E. Blaser, C. M. Kincaid, H. T. Bryant, and R. W.
Engel. 1959. Effect of full and restricted winter rations on dams
and summer dropped suckling calves fed different rations. J. Ani.
Sci. 18:21-31.
8. Hill, J. R. 1978. Interrelations of animal genetics and forage quality.
Advances in hay silage and pasture quality. American Forage and
Grassland Council. 62-65.
9. McCormick, W. C. , 0. M. Hale, and B. L. Southwell. 1958. Fattening steers
on small grain pastures. GA Agri. Expt. Sta. Bulletin N. S. 49.
84
BREEDING AND SELECTING LEGUMES FOR
GREATER N2-FIXATION AS SEEN BY
A MICROBIOLOGIST
By Harold L. Peterson
INTRODUCTION
The probability of successfully enhancing biological dinitrogen fixation
by Rhizobium spp in association with plants from the family Leguminosae has
perhaps never been greater than it is today. Our understanding of symbiotic
dinitrogen fixation has expanded tremendously during the last decade. Major
advances in the biochemistry, genetics and physiology of N2-fixing symbioses
have set the stage for significantly increasing dinitrogen fixation.
Recent attention has been focused on the potential of genetic engineering
in Np-fixation (Hollaender, 1977). While this concept is not new, it has
successfully stimulated the imaginations of many persons in the private, busi-
ness and government sectors of society. Indeed, long range improvements in
the N9~fixation process may depend on successful transfer of procaryotic "nif"
genes to eucaryotic organisms. However, immediate and intermediate range
improvements in N2~fixation will certainly depend on accelerated selection and
breeding of rhizobia-legume combinations for increased dinitrogen fixation.
This problem has been addressed since the discovery that bacteria in legume
nodules fixed atmospheric N2 for the plant, but recent progress in several
areas of research may remove some of the obstacles that have hindered develop-
ment of these rhizobia-legume combinations.
This paper will review recent procedures that show promise in helping
plant breeders and rhizobiologists select forage legume-rhizobia combinations
for enhanced dinitrogen fixation. The discussion will concentrate on the
rhizobial aspect of the symbiosis. Special attention will be given the chal-
lenge of establishing superior N2-fixing combinations of Rhizobium spp and
forage legumes in the field, and how selection and breeding can contribute to
successful establishment.
RHIZOBIUM - THE N2-FIXING MICROSYMBIONT
Characteristics
Bacteria belonging to the genus Rhizobium Frank (kingdom Procaryotae,
Division Bacteria, Order Eubacteriales , Family Rhizobiaceae) are differentia-
ted because of their ability to nodulate leguminous plants, and presumably fix
N2 within these nodules. These small, motile, pleomorphic rods are non-spore
forming and gram-negative. When grown on media containing substantial amounts
of carbohydrate, Rhizobium often produce a great deal of extracellular polysac-
charide (slime) and may develop cytoplasmic inclusions of poly-B-hydroxybuty-
rate. They are aerobic, but can tolerate 02 tensions less than 0.01 atm.
Optimum temperature for growth varies from 25 to 30 C, and pH from 5. 0-8. 5
85
(Buchanan and Gibbons, 1974) .
Rhizobia are often separated into two groups according to growth rate on
yeast-extract containing media, and the type and number of flagella. The fast
growers form distinguishable colonies on yeast extract - mannitol (YEM) agar
in 3 to 5 days; numbers of flagella vary from 2 to 6, and occur at lateral
positions on the bacterium (peritrichous) arrangement. Species within this
group are R. leguminosarum Frank, R.. phaseoli Dangeard, R. meliloti Dangeard
and R. trif olii Dangeard. Fred et al. (1932) indicated that Rhizobium
leguminosarum usually form nodules with species of Pisum, Lathyrus , Vicia ,
Lens and Cicer . Rhizobium phaseoli nodulate species of Phaseolus , and R.
meliloti species of Medicare, Melilotus and Trigonella. Rhizobium trif olii
form nodules on Trifolium spp .
The slow growers typically form colonies < 1mm in diam on YEM agar in 5
to 10 days; a single flagellum (monotrichous) may be present at polar or
subpolar sites on the bacterium. Two species are recognized: Rhizobium
j aponicum (Kirchner) Buchanan and Rhizobium lupini (Schroeter) Eckhardt.
Other strains of Rhizobium, mostly slow growing, are combined in a composite
group called cowpea rhizobia. Glycine spp are usually nodulated by R.
j aponicum, whereas R. lupini nodulates species of Lupinus and Ornithopus .
Cowpea rhizobia nodulate many genera of legumes such as Acacia , Arachis ,
Baptistia, Cassia , Caj anus , Crotalaria , Desmodium, Dolichos , Genista,
Lespedeza , Phaseolus , Pueraria , Stizolobium and Vigna (Fred et al., 1932).
Vincent (1977) has recently reviewed the characteristics and complexities
of Rhizobium, and the reader is encouraged to consult his paper for an excel-
lent and comprehensive discussion.
Isolation
The procedures used to obtain strains of rhizobia usually involve isola-
tion from legume nodules. Although selective media have been reported for
direct isolation of rhizobia (Greig-Smith , 1912; Graham, 1969), attempts at
direct isolation from soil have failed.
Vincent (1970) summarized the general procedure for isolation of rhizobia
from soil. Briefly, a legume is grown in contact with a selected soil and
nodules are allowed to develop. Representative nodules are removed from the
roots, surface-sterilized, and tissue containing rhizobia is transferred
aseptically to petri plates containing a sterile agar. ' Rhizobia-like ’ colonies
are cloned by repeated transfer until representative isolates from single-
cells are presumably obtained. These colonies are transferred to slants and
maintained in a fresh and highly viable condition. Finally, isolates are
verified as rhizobia by inoculating the host legume and growing the legume
under rhizobially controlled conditions, examining for the formation of root
nodules. New isolates of Rhizobium are characterized bacteriologically and
catalogued for further use.
The time involved from initial isolation through characterization can
involve as few as 10 weeks with R. trif olii to 6 months with slow growing
cowpea rhizobia, assuming of course that everything goes according to plan.
Unfortunately, problems with rhizobial contamination, growth chamber failure,
leaky greenhouses etc. can double or even triple the amount of time required
to obtain a new strain of Rhizobium.
Unfortunately, current isolation procedures are very inefficient in
86
obtaining strains of Rhizobium differing markedly in ^-fixation. For example,
we obtained 195 isolates of ' rhizobia-like ' bacteria from nodules for Trifolium
pratense L. CV. 'Kenland' , Trifolium incarnatum L. CV. 'Tibbee' , and Trifolium
vesiculosum Savi. , CV. ’Meechee’. All isolates were cloned and reinoculated
on the host legumes, yielding 129 strains of R. trifolii. Analyses of plant
dry matter and acetylene reduction (still in progress) suggest that N2-
fixation by only three strains differed significantly from the overall mean.
All three of these strains are ineffective.
Strains of Rhizobium vary considerably in a wide range of characteristics,
including morphology, physiology, serology and ecology. Many studies have
reported variations in these characteristics (Vincent, 1977). A detailed
reiteration is not within the scope of this paper, and the reader is referred
to the review by Vincent (1977) for further details.
GENETIC VARIABILITY
The nodulation process is controlled genetically by both the leguminous
plant and the rhizobia, with the plant exerting perhaps the greater controlling
influence (Nutman, 1969). Despite the abundant phenotypic evidence implying
extensive genetic variability within natural populations of rhizobia, little
progress has been made in genetic mapping of Rhizobium spp , especially in
relationship to nodulation and N2~fixation.
Genetic variability among rhizobia would seem to be partially responsible
for the host-plant specificities that have been noted in many of the forage
legumes. In the light of Vincent’s (1977) discussion, it seems probable that
this specificity occurs in many, if not all, of the steps involved in the
nodulation process.
Certainly, the stimulation of Rhizobium spp in the rhizosphere of legumi-
nous plants has been documented (Nutman, 1965, 1969; Vincent 1974; Dart, 1974,
1977; Parker et al. , 1977). However, the biochemical (not to mention genetic)
explanation is lacking for the preferential stimulation of certain strains in
the rhizosphere. Rhizobia compete with other soil microorganisms (including
other rhizobia) for available organic and inorganic nutrients in soil. Legume
root exudates enhance the growth of Rhizobium spp in the rhizosphere (Dart,
1974). Parker et al. (1977) have shown that coldwater extracts of soil can
support the multiplicaton of R. trifolii and _R. lupinj^ from an initial density
of 1CP viable cells/ml to a final density of 2-4 x lO^/ml . These extracts
were obtained from a 1:1 water-to-soil ratio (v/w) . Competition is important
in suppressing rhizobial growth and may be very intense in soils of the south-
ern U.S. where numbers of rhizobia rarely exceed 10^/g (Peterson, unpublished).
The infection process is another area where genetic variability among
strains of Rhizobium influences the processes of nodulation and N2~fixation.
Nutnam (1953) found that strain C13R of R. trifolii lost the ability to nod-
ulate TL pratense . Purchase (1953), Purchase and Nutman (1957) used a non-
nodulating strain of R.. trifolii to inhibit nodulation of red clover by a
normal virulent strain.
Trifolium ambiguum is another interesting example involving a host-strain
interaction limiting nodulation. Parker et al. (1949), Parker and Allen
(1952) found that T_. ambiguum rarely forms nodules with most strains of R.
trifolii . Hely (1957) found that strains of R. trifolii from Turkey were much
more efficient in nodulating _T. ambiguum than strains of R. trifolii isolated
from soil in New Zealand.
More recent work may be providing an explanation for the inabiltiy of
certain strains of Rhizobium to infect leguminous plants. Dazzo and Hubbell
(1975) established that cross-reactive antigens were present in cell walls of
compatible combinations of R. trif olii and T_. repens CV. 'Louisiana Nolin' and
X* f ragif erum L. CV. 'Salina' . If a strain of R. trif olii lost infectiveness,
a portion of the antigenic homology was also lost. Antigenic homology was
absent between T_. repens and isolates from the other Rhizobium spp.
A clover lectin was isolated that would bind infective but not noninfec-
tive strains of R. trif olii . The lectin facilitating the agglutination is
sensitive to acid, alkali, pronase, trypsin, periodate and urea, suggesting
that the material is protein (or glycoprotein) .
Dazzo, Napoli and Hubbell (1976) found that noninfective strains of R.
trif olii and strains of R. melioti are absorbed in similar yet small numbers by
T_. repens root hairs. However, infective R. trif olii cells were absorbed in
numbers nearly five times greater. A 2-deoxyglucose-sensitive receptor site
was implicated as the molecular point of coordination present in both clover
roots and rhizobial cells. Further verification of these findings has been
provided by Dazzo and Brill (1977).
Genetic variability within the legume host and rhizobia is probably also
expressed in the formation of infection threads. Work by Lim (1963) indicates
that infection is proportionally related to the number of rhizobia present in
the rhizosphere. However, when the first nodule is formed, an increased
number of bacteria are required to promote futher infection. Purchase and
Nutman (1957) noted that formation of the first nodule in T_. pratense resulted
in much larger numbers of rhizobia being required for the formation of addi-
tional nodules. The reasons for inhibition of further nodulation are unknown.
Hubbell et al. (1978) found that strains of Rhizobium spp that typically
infect the legume root via root hairs can produce low levels of pectinolytic
enzyme activity. This finding is very important since it reinforces Nutman' s
(1956) "invagination" hypothesis of infection. It also represents another
source of variablity, and may explain why some infection threads abort. If the
outer cell-wall of a root hair must be removed enzymatically in close coordi-
nation with the growth of the infection thread, variation in pectinase activi-
ties of the rhizobia may be very important in determining whether or not the
infection thread will reach the root cortex. This may explain the observation
of Nutman (1949) that infection threads do not form if rhizobia penetrate the
lumen of the root hair.
Once the nodule has formed, genetic factors in both rhizobia and plant
govern the effectiveness of the ^-fixation process. Holl and LaRue (1976)
have listed the plant genes known to regulate N2~fixation in several legumes,
including _T . pratense . Within natural populations of Rhizobium, individual
organisms vary considerably in ^-fixation capacity. In R. trif olii , Bergersen
et al. (1971) found significant variation among isolates in effectiveness of
N2~fixation with sampling areas and sampling years. The effectiveness of most
R.. trif olii isolates from three of four sites in southeastern Austrailia on T_.
subterraneum was only 70 to 85% as great as the control (strain TA1) . Approxi-
mately 57 of 420 isolates exceeded TA1 in effectiveness of N2~fixation as
determined by dry-matter accumulation. The remaining isolates were only 20-90%
as effective. Natural isolates of _R. trif olii from 7 locations were only 78%
as effective in fixing N2 as strain TA1. Gibson et al. (1975) found substan-
tial variability in effectiveness of R. trifolii isolates from eight regions of
southeastern Australia over a five year period. As in the work reported by
88
Bergersen et al. (1971) most isolates were inferior to TA1 in fixing N2.
Despite abundant phenotypic evidence implying extensive genetic varia-
bility to nodulation of Np-fixation within rhizobia, little progress has been
made in genetic analysis and mapping of Rhizobium spp . The main handicap to
understanding the genetics of ^-fixation is a lack of techniques for analyzing
phenotypic expression by rhizobia without using leguminous plants (Swinghamer,
1977). This restriction may soon be removed, because Tepkema and Evans (1975),
Pagan et al. (1975), Kurz and LaRue (1975) and McComb et al. (1975) have ob-
tained ^-fixation (or C2H2 to C2H4 reduction) in pure cultures of several
Rhizobium spp. The stage has been set for some very exciting and important
breakthroughs in biological ^-fixation by the Rhizobium-legume symbiosis.
SCREENING STRAINS OF RHIZOBIUM FOR N2-FIXATION
WITH LEGUMINOUS PLANTS
Classical tests for compatibility between rhizobia and leguminous plants
are based on the extent of plant growth when inoculated with a strain of
rhizobia and grown in a nitrogen-free media. Usually these tests are conducted
in the greenhouse or growth chamber under ' rhizobially-controlled ' conditions.
An effective strain of rhizobia is usually included as a positive control so
that the relative capacity for ^-fixation can be established by the unknown
strain(s) . This type of test is more valuable for forage than grain legumes
because N-content and dry matter production are more closely related in forage
legumes (Erdman and Means, 1952), and the onset of seed production in forage
legume does not seem to dominate plant activities as extensively as in grain
legumes (Burton, 1976).
Screening can be carried out in a variety of containers such as tubes,
crocks, bottomless-bottles (Burton, Martinez and Curley, 1972; Gibson, 1963)
and plastic pouches (Weaver and Frederick, 1972). Unfortunately, determining
the N2~fixation potential of a strain requires that growth continue until
significant differences appear in nitrogen content or dry matter production
among plants. The time required for these differences to appear varies con-
siderably among legume species. Gibson et al. (1975) were able to separate R.
trif olii isolates using T_. subterraneum CV. 'Bacchus Marsh' at 31 days after
planting. Large-seeded legumes may require more time to overcome the initial
influence of nitrogen in the seed.
An important new screening technique was introduced by Wacek and Brill
(1976). They developed a rapid assay for screening ^-fixation ability of
soybean cultivars and rhizobia. Inoculated seeds are planted in 20 ml serum
bottles containing sterile vermiculite and plant growth solution. A sterile
plastic bag is placed over each bottle and loosely fastened to permit gas ex-
change. After 14 days growth, the shoot of the plant is removed and the
container stoppered. N2~fixation is then measured via an acetylene- to-ethylene
reduction procedure. The technique has recently been applied to screening
forage legumes and strains of Rhizobium for effectiveness of N2~fixation
(Maier and Brill, 1976).
Plant tissue culture is another system that may be applicable to rapid
screening of rhizobia for N2~fixation. Child and LaRue (1976), for example,
developed a tissue culture system that was used to determine nitrogenase acti-
vity of rhizobia within 14 days of inoculation. Interestingly, Child and LaRue
see little advantage in using tissue culture for routine screening analyses.
They indicate that more time, expense and energy were involved with tissue cul-
89
I
ture than in standard grow-out procedures, an assertion that may be somewhat
debatable .
Pierce (1978) has described work of Dr. Don Barnes and colleagues on
improving ^-fixation by Medicago sativa L. and Rhizobium meliloti . Dr. Gary
Heichel is developing a new growth chamber system for simultaneous, non-de-
structive, whole-plant studies on photosynthesis and N2~fixation. It is hoped
that characterization of CO2 exchange, acetylene-to-ethylene reduction and
uptake will help define the relationship between the photosynthetic capacity of 1
legumes and the ^-fixation capacity of rhizobia. This should lead to improved
legume-rhizobia combinations that are capable of enhanced N2~fixation and
protein production.
We have developed a plastic-pouch procedure that can be used to measure
N2~fixation (C2H2 to C2H4 reduction) activity of nodulated forage legumes
(clovers) (Peterson, in preparation) . The technique involves growing inocu-
lated plants in plastic pouches similar to those described by Weaver and
Frederick (1972). A vacutainer needle is placed in the open end of each pouch.
The pouch is then sealed to the stems of the plants (and vacutainer needle)
using a material developed for sealing automobile windshields. Air is removed
from the pouch and a known volume of a 90:10 mixture of (Ar + O2) and (C2H2) is
injected into each pouch. Ethylene production is determined using a gas
chromatograph with C2H2 serving as an internal standard. The principal advan- 1
tages of the technique are that it requires very little growth chamber space,
contamination by exogenous rhizobia is reduced, and plants may be analyzed
repeatedly without apparent damage to either the plant or rhizobia in the
nodules .
THE ULTIMATE TEST - ESTABLISHING SUPERIOR RHIZOBIUM-LEGUMINOUS
PLANT COMBINATIONS IN THE FIELD
Laboratory and greenhouse screening can be used to select rhizobia-
leguminous plant combinations with greater potential for ^-fixation. But
until we produce forage and grain legumes on a commercial basis in greenhouses,
the ultimate test is the ability of a selected combination to perform in the
field (Burton, 1976; Date, 1976; and many, many others).
Soil, unfortunately, is a rather inhospitable environment for both legumi-
nous plants and rhizobia. Factors that effect the survival of both plant and
rhizobia include soil temperature, moisture, pH, drainage, nutrient availa-
bility, pesticides and other additives, pathogenic and antagonistic microorga-
nisms, presence of beneficial microorganisms, management, and time. Each of
these factors has received considerable attention in recent reviews (Gibson,
1976, 1977; Mulder et al., 1977; Parker et al., 1977, Munns, 1977; Sprent,
1976) .
Perhaps our concept of centers of excellence in research may need a minor
modification. Plant-rhizobia combinations that prove successful in one region
of the United States may fail in another region. This shortcoming can be
avoided if the scientists performing the greenhouse and growth chamber screen-
ings will employ conditions that represent the extremes encountered by the
plant in its cultivation throughout the country. Also, as combinations are
developed, field testing should be conducted at representative sites where the
legume is grown and not confined to the region where the combination was
developed .
90
In our work with annual clovers, three problems are receiving priority.
The first problem is isolating and collecting strains of R. trifolii that are
compatible with lines of T_. incarnatum, T_. vesiculosum and T.. subterraneum
being developed by Dr. W. E. Knight. This involves requisitioning cultures
from throughout the world using the literature as a guide for strain selection,
and the soon-to-be-revised IBP World Catalogue of Rhizobium Collections (Allen
and Hamatova, 1973) as a source index. Strain isolation has proven a time
consuming and f rustratingly inefficient process. Work is underway to develop
improved procedures for isolating superior ^-fixing strains of R. trifolii
from natural populations. Hopefully, a new procedure will be perfected soon
for use in the isolation process.
The second problem is coupling the legume-rhizobia selection process
(winter annuals) with the reality of a field management system that usually
requires incorporation of a cool-season grass with the legume for adequate
late-fall and winter grazing. Strains of Rhizobium must be selected that will
nodulate clover in the presence of nitrogen fertilizer (ie. 20-60 kg N/ha) used
to promote early growth of the grass.
The third problem is developing inoculation materials and procedures that
will insure maximum nodulation in the field by the superior strains of
Rhizobium. On the surface this problem seems so basic that most people assume
it has been solved. However, Weber (1977) has recently pointed out that the
technology has not been perfected that will insure nodulation by an inoculated
strain in soils already containing a population of host-infective rhizobia.
The problem is aggravated in Mississippi because winter-annual clovers are
usually planted during late August or early September. Soils are usually dry,
and seeds may be subjected to temperatures of >40 C during a 1 to 2-week period
after planting. Seed-borne rhizobia die very rapidly when exposed to tempera-
tures greater than 40 C (Kremer and Peterson, unpublished).
Much work remains to be done. Hopefully through close cooperation between
plant breeders and rhizobiologists , superior ^-fixing Rhizobium- legume com-
binations can be obtained to help provide the high quality forages necessary
for production of animal protein.
SUMMARY
Close cooperation between legume breeders and rhizobiologists should
result in the development of plant-rhizobia combinations that can fix greater
amounts of N2 from the air. In achieving this goal, the breeder and rhizo-
biologist must continually interact in the selection process. New, more rapid
and sensitive screening procedures being developed hold great promise in al-
lowing efficient and rapid selection of superior N2~fixing combinations. Field
testing is the final and perhaps most important step before a plant-rhizobia
package can be recommended for adoption by producers. The main problem with
field inoculation of legumes (following nearly 80 years of work) is lack of an
inexpensive, dependable inocula to insure nodulation by the inoculated strain
(s) , especially in thermic soils that already contain less-effective, infective
rhizobia. The current emphasis on genetic engineering for improved N2~fixation
will be an exercise in academic futility unless efforts are made to concur-
rently develop improved inoculation procedures and improved understanding of
the ecology of rhizobia in soil.
91
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Burton, J. C. , C. J. Martinez and R. L. Curley. 1972. Methods of Testing
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Dart, P. J. 1974. The infection process. Ln A. Quispel, ed . The Biology
of Nitrogen Fixation. pp 381-429, American Elsevier, New York.
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Gibson, A. H. 1976 a. Recovery and compensation by nodulated legumes to
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William E. Newton and C. Y. Nyman, ed. Proceedings of the 1st
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of Rhizobium trifolii associated with Trifolium subterraneum L. pastures
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Holl, F. B. and T. A. LaRue. 1976. Genetics of legume plant hosts. Ln
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93
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mutant strains of Rhizobium japonicum. J. Bact. 127:763-769.
McComb, J. A., J. Elliott and M. J. Dilworth. 1975. Acetylene reduction by
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Mulder, E. G. , T. A. Lie and A. Houwers. 1977. The importance of legumes
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A Treatise on Dinitrogen Fixation, Sect. IV. pp 221-242. Wiley-
Interscience , New York.
Munns, D. N. 1977. Mineral nutrition and the legume symbiosis, jin. R. W. F.
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Parker, D. T. and 0. N. Allen. 1952. The nodulation status of Trifolium
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Weaver, R. W. and L. R. Frederick. 1972. A new technique for most-probable-
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p 433. Pleunum Press, New York.
95
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
INTRODUCTION: COMPLEXITY AND CHALLENGES
By Pryce B. Gibson
Our panel is concerned with the forages that are grown in mixed stands.
Usually these mixed stands are harvested by grazing livestock. Therefore, we
are concerned with a plant community instead of one species and we are con-
cerned with an important biological entity--the grazing animal. Obviously,
the plant community and the grazing animal contribute variables to research
involving the crops. I believe it is self evident that the complexity of
research usually increases with the addition of variables and, therefore,
research on the forage crops used in mixed stands is more complex than
research on the crops used in pure stands.
Most mixed stands of forage crops involve a grass and a legume. The two
species are intimately associated, mutually affect the microclimate, and
compete for the essentials for growth. Consequently, the ecological inter-
actions of a mixture are more complex than those of a monoculture. Contribu-
tions of the partners to the environment and the performance of the mixture
are partly competitive and partly comp! ementary . Legumes supply biologically
fixed nitrogen, increase the quality of the forage, and may improve the
seasonal distribution of production. Grasses supply fiber that is needed in
the ruminant's diet, reduce the chance of bloat, reduce trampling damage,
provide the legume some protection from low temperatures , and may, by serving
as a trap crop, reduce the number of some nematodes. The complicated ecolog-
ical interactions of mixed stands indicate that the true test of a cultivar
is its performance in a mixed stand that is subjected to the stresses and
interactions caused by normal use. Obviously, the relative importance of
testing a cultivar in a mixed stand rather than in monoculture may vary with
annuals, perennials, cool season crops, warm season crops, location and
management.
The success of a grass-legume mixture depends upon the mutual compati-
bilities and contributions of the two species. The two are a team and each
species should have characteristics compatible with the needs of the other. A
draft horse and a race horse make a bad team regardless of the fine breeding
of each because the members of the team are not compatible. Maximum aggress-
iveness that may be a desirable attribute of a forage for growth in a mono-
culture may be objectionable for growth in a mixture. The success of a
mixture depends on the breeder of each species considering the characteristics
needed for success of the mixture, not for supremacy of his species.
I have encouraged panel members to comment on the following statements
and questions: (1) "Forage breeders should make more selections and conduct
more strain tests in mixtures as the crops are used, thereby testing the
96
compatibility of the entries and the ability of the legumes to supply nitrogen
for both crops". (2) "Should breeders of pasture species use grazed areas in
lieu of cultivated space planted nurseries and by so doing evaluate plants
under actual pasture conditions?" This approach would substitute the grazing
animals for some labor and is particularly applicable to breeding for improv-
ed persistence of stands under grazing. Unfortunately , implementing this
approach is difficult and the plant breeder must control time of grazing.
However, once implemented this approach may be more efficient than tradition-
al methods. Also, I have suggested that each plant breeder include remarks
on:
1. Extent of crop use in mixture vs in pure stands.
2. Advantages and problems of mixtures vs pure stands from the
standpoint of forage production and utilization.
3. Comments relative to breeding and testing (e.g.: What are the
plant characteristics and other components that affect the
success of the mixture and the species in the mixture? What
consideration of compatibility for growth with other species
should be included in the breeding program?).
Partly because forage research involves several species and several
variables, procedures and priorities used in forage breeding vary. Conse-
quently, differences in opinions exist and probably will surface in our
presentation. Although the make-up of our panel is diverse, our topic should
be of interest to all concerned with forages. If alloted time permitted we
logically should have included an entomologist and a plant pathologist to
discuss insects and diseases in mixtures vs in pure stands. Because our time
is limited, we are depending upon our crop ecologist and other panel members
to consider insects and diseases.
97
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
SUMMARY OF ECOLOGICAL CONSIDERATIONS
IN RELATION TO THE BREEDING AND DEVELOPMENT OF
LEGUME CULTIVARS WHICH CAN BE GROWN IN GRASS-LEGUME MIXTURES
By 0. Chari es Ruel ke
Ecological considerations are the first and probably the most important
considerations in breeding legumes which can be grown successfully in grass-
legume mixtures. Until specific species of legumes and grasses are found
which are compatable in mixtures, efforts to improve either the legume or
grass have little chance for success. However, breeding for compatabil ity and
persistence of legume and grass species which have a potential in mixtures,
can greatly enhance the performance of each species and result in far better
production from the grass-legume mi>aure than from either species grown alone.
Many factors of the environment need to be considered when establishing
grass-legume mixtures. First, and most important, is the temperature factor.
No single species of grass or legume can be expected to be productive in the
middle of the hot summer and also the middle of the cold winter. However,
with proper selection of certain perennial s and or self-seeding annuals,
maximum production is possible, either during the warm or during the cool
season. It is also possible to select species to produce alternately, namely,
bahiagrass in the warm season and white clover in the cool season. Many
combinations can and need to be considered.
Proper soil moisture like temperature can be the critical and or deciding
factor in selecting and breeding grasses or legumes for mixtures.
Soil fertility often limits certain species from mixtures and the competi-
tion between species for the nutrients often determines if or which species
will persist.
Light intensity and photoperiodic response are also very important from
the standpoint of establishment of the reseeding species as well as to whether
an established species will flower and make seed.
The biotic factor including the harvesting by man, animals, caterpi 1 1 ars ,
or parasitism by plant diseases are factors of significant importance
Ultimately, it is the effects of one plant on another that limits the
production of a mixture. It is this effect that the breeder must deal with.
In pure stands of a single species, most of the plants are bred to germin-
ate and emerge at the same time. In mixtures one species may germinate or
resume growth earlier than another, thus taking up the moisture and nutrients
or forming a canopy to reduce the light on the other species.
Plant growth habit, which may be erect to prostrate, can be altered by
breeding so that species compete more or less. Leaf angle, which may be acute
or obtuse, can be altered which may increase the efficiency of use of light.
Presence or absence of pubescence or waxy leaf coat can be altered by breeding
which could alter water loss rates, or insect and disease resistance. These
are but a few examples of ways the plant breeder could alter legumes for use
in mixtures.
Finally, the growth habit, growth rate, and recovery rate of any one of
the species in a mixture can be altered by management. Therefore, the testing
98
of any new breeder lines in mixtures should be done by clipping trials, to
simulate use as green chop or hay, as well as by grazing animals to evaluate
the response under grazing.
99
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
IMPORTANCE OF MIXED STAND EVALUATION IN BREEDING
AND VARIETY DEVELOPMENT- -ANNUAL LEGUMES1
By W. E. Knight
In I960,. Henson and Hollowell listed over 40 species of
winter annual legumes adapted to the South. A number of these
species that were of economic importance between 1945-1955 are no
long available commercially.
Most annual legumes grow well in pure stands or in mixtures.
The winter annual clovers are grown primarily in mixtures with
ryegrass and/or cereals on prepared seedbeds and overseeded on
permanent grass sods. Vetches may be grown in mixtures but have
been used primarily as cover crops. The lupines are used for
grazing and soil improvement and are usually grown in pure stands.
When grown for grazing, they may be seeded alone or in mixtures
with cereals.
At one time, an estimated 6-7 million acres of annual
lespedezas were grown in the region. Most of this acreage was
in mixed stands with summer perennial grasses.
Results of a survey completed in 1977 indicate a renewed
interest in legumes and an increased breeding effort (Table 1).
This survey indicates breeding or selection in 16 annual legume
species .
According to Johnson and Byer evaluation of forage species
to be grown in mixtures is complex and the researcher is faced
with the problem of breeding for compatibility. A multidiscipli-
nary approach to breeding and evaluation is necessary for rapid
progress and essential to produce the forage legumes needed in a
grass-legume system. The present demand for, and potential use
of, improved forage legumes demands the initiation of coordinated
improvement programs among plant breeders, pathologists, entomolo-
gists, microbiologists, soil scientists and seedsmen to meet the
forage legume needs of the livestock industry. There is a lack
of definitive information on fertilizer requirements of grass-
legume pastures as related to persistence, quality, and inter-
actions of applied nitrogen with legume Rhizobia including the
interactions of sulphur and molybdenum as related to rhizobium
ef f iciency .
The evaluation phase of the breeding program should seek
answers to the following:
1. What management practices are necessary for establishing and
maintaining grass-legume mixtures?
1/ Cooperative investigations of the Mississippi Agricultural and
Forestry Experiment Station and the Plant Science Laboratory,
SEA, FR, U.S. Department of Agriculture, Mississippi State,
Mississippi 39762.
100
Table 1. Forage legume species in public improvement programs in the Southeastern United States 1/
CQ
CQ
PS
CQ
PS
PQ*'
CS
CQ~
PS
pq~
CQ
CQ
CQ
PS
CQ
PS PS
PQ W CQ
PS
cq~
PS PS PS
PQ CO CO
CQ
PS PS
CQ CO
CQ
PS
CO
PS
CO
CQ
CQ
CQ
CQ
PS
CQ CQ"
PS
cq~
CQ
PS
CQ CO CO
PS PS
CO CO
CQ
CO
PS
TO W CQ PQ
CQ
PS
ccf
PS
CQ CQ~
PQ
PS
CQ1
PS
PQ~ CQ
t>
t>
03
r— 1
a
M
•H
cc
T3
CD
CD
cs
+->
P 0
CD
P -H
i — l
CS -P
!
o
CS CD
•H ( — 1
CD
CD
S C/5
P TS
QJD
O 03
U
cs cs
, o
b £ -h
CS P>
•H cS
"d d
Q> rH
CD o3
iS >
CQ W
II II II
CQ CQ PS
101
Release probably within 5 years.
2 .
Can minimum tillage practices be used successfully to
establish new stands and reestablish clovers when stands are
lost? (Non-point pollution).
3. What soil fertility management is necessary for optimal
nutritional forage quality including fertility interactions
as related to legume survival and rhizobial efficiency?
4. What are the causes of stand failures and lack of persis-
tence (insects, diseases, nematodes, etc.)?
5. What is the potential of supplemental water as related to
maintaining production, quality, and persistence and in
regard to timely establishment of fall seeded crops?
6. What is the potential for reseeding as compared to maximum
utilization and annual reseeding?
7. What is the economic advantage, if any, of a harvested seed
crop from a grass-legume system?
REFERENCES
Adams, W. E., and McCreery, R. A. 1959. What are the fertility
needs of crimson clover when grown with Coastal bermudagrass and
Coastal bermudagrass grown alone? Better Crops Plant Food.
43(4): 6-15.
, and Stelly, M. 1958. A comparison of Coastal and
common bermudagrass (Cynodon dactylon (L) Pers.) in the piedmont
region: Yield response to fertilization. Agron. J. 50: 457-459.
Allen, 0. N. 1973. Symbiosis: Rhizobia and leguminous plants.
In Maurice E. Heath, Darrel S. Metcalfe, and Robert F. Barnes
(eds.), Forages: The Science of Grassland Agriculture, pp. 98-
104. Iowa State University Press, Ames.
Dawson, M.D. , and Bhella, H. S. 1972. Subterranean clover
( Trifolium subterraneum L. ) yield and nutrient content as in-
fluenced by soil molybdenum status. Agron. J. 64:308-311.
Dillard, J. G. 1972. The place for annual legumes in the
Southeast: An economist viewpoint. Rep. 29th South. Past. For.
Crop Impr. Conf., Plant Sci. Res. Div. , Agric. Res. Ser. , U. S.
Dept. Agric. (Rep.) PSR-47-71, pp . 105-111.
Erdman, L. W. 1959. Legume inoculation: what is it - what it
does. U. S. Dep . Agric. Farmers Bull. 2003, 16 pp .
Henson, P. R. and Hollowell, E. A. 1960. Winter annual legumes
for the South. USDA Farmers Bulletin No. 2146, 24 pp .
Jacobs, V. E. 1973. Forage production economics. Chap. 3. I_n
M. E. Heath, D. S. Metcalfe, and R. F. Barnes, Forages. Iowa
State University Press. Ames, Iowa.
102
Johnson, I. J., and Beyer, E. H. 1973. Forage Crop breeding.
In M. E. Heath, D. S. Metcalfe, and R. F. Barnes (eds.), Forages:
The Science of Grassland Agriculture, pp . 114-125. Iowa State
University Press, Ames.
Knight, W. E., Palmertree, H. D. and Watson, V. H. 1976.
Growing subterranean clover in Mississippi. Miss. Agric. Exp.
Sta. Inf. Sheet 1268, 2 pp.
, and Hoveland, C. S. 1973. Crimson clover and
arrowleaf clover. I_n Maurice E. Heath, Darrel S. Metcalfe, and
Robert F. Barnes (eds.), Forages: The Science of Grassland
Agriculture, pp. 199-207. Iowa State University Press, Ames.
Leffel, R. C. 1973. Other legumes. ^n. Maurice E. Heath,
Darrel S. Metcalfe, and Robert F. Barnes (eds.) Forages: The
Science of Grassland Agriculture, pp. 167-176. Iowa State
University Press, Ames.
Offutt, M. S., and Baldridge, J. D. 1973. The lespedezas. I_n
M. E. Heath, D. S. Metcalfe, and R. F. Barnes (eds.). Forages:
The Science of Grassland Agriculture, pp. 189-198. Iowa State
University Press, Ames.
Templeton, W. E., Jr., and Taylor, T. H. 1975. Performance of
bigflower vetch seeded into bermudagrass and tall fescue swards.
Agron. J. 67:pp. 709-712.
Wade, R. H. , Hoveland, C. S., and Hiltbold,. A. E. 1972. Inoculum
rate and pelleting of arrowleaf clover seed. Agron. J. 64:481-
483.
103
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
BREEDING ANNUAL GRASSES FOR USE IN
GRASS-LEGUME MIXTURES
By C. E. Watson, Jr.
Cool-season annual grasses, including ryegrass, wheat, oats, rye, and
triticale, are widely used for winter pasture in the southeastern United
States. Annuals provide an excellent source of high quality forage during
periods when warm-season perennials are dormant. These species are grown
alone or in combination with legumes on prepared seedbeds or permanent grass
sods. Annuals are very aggressive species and are highly competitive with le-
gumes in mixed swards.
ADVANTAGES OF MIXED SWARDS
Several benefits are realized by growing annual grasses with legumes.
These include:
1. The legume component can fix nitrogen symbiotically .
2. The inclusion of a legume provides improved forage quality over pure
grass .
3. There is less chance of bloat.
4. The fibrous grass root system makes for better footing, less tram-
pling damage, and may prevent some heaving damage to the legume.
5. The legume reduces the tetany potential.
6. There is a better seasonal distribution of yield.
DISADVANTAGES OF MIXED SWARDS
Among the disadvantages associated with grass-legume mixtures are:
1. A higher level of management is required to maintain the botanical
composition. Fertility and liming practices, seeding rates, fre-
quency and height of defoliation, and choice of species are critical
factors in the establishment and maintenance of a desired botanical
composition.
2. Weed control is more difficult, particularly with annuals.
3. Disease problems may be more severe in mixed stands.
BREEDING FOR COMPETITIVE ABILITY
Breeding programs for species that will be used in mixtures should in-
clude mixed stand evaluations during some phase (s) of the programs. However,
there are a number of problems regarding mixed stand evaluations which the
breeder must consider in selecting genotypes or cultivars for competitive
ability.
The question arises as to whether mixed stand evaluations should be in-
cluded in the selection phase or only in the testing phase of the breeding
program. To date, mixed stand evaluations have generally been carried out
104
only in the later stages of breeding programs to cut down on the number of
plants and the amount of time, labor, and land involved. However, to relegate
mixed stand evaluation to the testing phase alone, with no prior selection for
competitive ability, may result in little or no improvement in competitive
ability. Reports vary as to the correlation between performance in pure stand
and performance in mixed swards (13,14,16).
Several planting arrangements have been used to evaluate forages in mixed
stands. These include broadcast, alternate row, and mixed row plantings.
Broadcast and mixed row plantings have generally resulted in higher yields
than alternate row plantings (5,9,18,22), although Hanley et al. (11) found no
differences between alternate and mixed rows. Lack of uniform competition may
pose a problem with broadcast and mixed row plantings. If alternate or mixed
row plantings are used attention must be given to the distance between rows,
as the effects of competition decrease rapidly with increasing distance be-
tween rows or plants within rows (9,22). The use of alternate plants of
grasses and legumes or spaced grass plants surrounded by legumes offer alter-
native planting arranagements , but involve more time and labor.
The performance of forages tested in mixed swards may differ under graz-
ing and clipping. Forages tested under grazing are subject to trampling, soil-
ing, and selective grazing, which are not accounted for under clipping.
Bryant and Blaser (4) noted that estimating grazing yields from clipping data
may lead to inflation of yields. The bunchy growth habit of annual grasses
may cause selective grazing problems in mixed swards (2). To minimize this
problem all species included in a mixture should be highly palatable. If plots
are to be grazed, frequency and height of defoliation and stocking rates must
be closely monitored. As a general rule, frequent low defoliation and high
stocking rates leads to clover dominance, while infrequent higher defoliation
and lower stocking rates results in grass dominance (2,8,19). However, species
vary in their response to grazing (4,15,19).
The nature and level of competition in mixed stands can be manipulated by
management practices. The breeder may use optimal management practices where
there is only competition for light or he may elect to limit additional fac-
tors, such as nutrients and water, in selecting for competitive ability. Le-
gumes have a higher nutrient requirement for potassium, phosphorus, and sulfur
than do grasses (2,19). Grasses are highly competitive for these elements,
particularly potassium, and deficiencies lead to grass dominance (1,2,8,19).
Grasses are generally more tolerant of excesses and deficiencies in soil mois-
ture (2). Rossiter (19) noted that dry years resulted in a higher percentage
of grass and wet years resulted in a higher percentage of clover, particularly
if rainfall occurred at the time of seeding. High seeding rates of aggressive
annual grasses will lead to grass dominance (3,5).
Grass cultivar x legume cultivar (arid species) and mixture x environment
interactions have been reported for mixed stand evaluations (4,7,9). The grass
breeder is faced with question of how many legume varieties and species, years,
and locations to use in mixed stand evaluations to provide reliable estimates
of competitive ability. This can become very expensive in terms of time,
labor, and land, particularly with annuals which must be reseeded each year.
The breeder should consider the specific factors which cause the decline
of a species in mixed stands, such as competition for water, light, or nu-
trients. Many of these problems may be easier solved with pure stands.
Several characteristics of annual grasses might be manipulated in pure stands
to improve their performance in grass-legume mixtures.
105
Blaser et al. (1) suggested the use of less vigorous grasses to maintain
legumes in mixed swards. Jennings and Aquino (12) stated that characteristics
that increase size and vigor early confer competitive ability in rice. Annual
ryegrass seedlings are extremely vigorous and aggressive compared to other
grasses (1,2, 3, 6). The rapid germination time and seedling growth rate of an-
nual ryegrass give it an early advantage and may cause it to become the ag-
gressor in mixed swards (2,6). The breeder might consider selecting annual
grasses with slower rates of germination and seedling growth, for use in mix-
tures. Seedling growth characteristics show variation among species and
varieties within species (3,6).
A reduction in the capacity of grasses for luxury consumption of potas-
sium would also help to maintain legumes in mixtures (8). Grasses are more
competitive for potassium than legumes, although their potassium requirement
is lower (1,8,9,19). If grasses germinate faster or initiate growth earlier
in the spring, they may cause a potassium deficiency in the legume and thus
become the dominant species. Fyfe, and Rogers (9) found differences between
varieties of tall fescue for their ability to take up potassium.
Alteration of the morphology of the grass plant may offer some possibili-
ties in selection for competitive ability. Jennings and Aquino (12) found
that tiller and leaf number, leaf length, spreading growth habit, leaf area
index, dry weight, and height were greater in strong competitors. Tall erect
bunch grasses tend to be more aggressive than prostrate types under infrequent
defoliation (2,8,17). Prostrate types are more competitive under frequent
defoliation, probably due to the fact that they are not completely defoliated.
Rhodes (17) suggested the development of cultivars with erect tillers and long
rigid leaves for systems of optimum defoliation (95-100% light interception).
For systems of frequent defoliation he recommended cultivars with prostrate
tillers and short leaves. However, Sakai (20) noted that it was difficult to
relate competitive ability to any single morphological trait.
Disease resistance is an important trait in breeding annual grasses for
use in mixtures. Templeton et al. (21) reported that the environment near the
ground in mixed swards was ideal for the development of disease. The resistant
species in a mixture will become the aggressor.
Genetic variation for competitive ability exists among species, varieties,
and genotypes within varieties (2,3,9,20). Donald (8) noted that competitive
ability as an aggregate character is lowly heritable, but that selection for
individual factors influencing competitive ability may show much higher herita-
bilities. Hamblin and Rosielle (10) found that estimates of heritability and
genetic variances from mixed stands tended to be unreliable due to competition
effects. The breeder who is selecting for annual grass genotypes that will
perform well in mixtures is faced with a complex problem. He must decide on
the nature and extent of mixed stand evaluations in the selection process,
realizing that many factors can influence the performance of mixed stands.
REFERENCES
1. Blaser, R. E. and N. C. Brady. 1950. Nutrient competition in plant as-
sociations. Agron. J. 42:128-135.
2. Blaser, R. E. , W. H. Skrdla, and T. H. Taylor. 1952. Ecological and
physiological factors in compounding forage seed mixtures. Adv. Agron.
4:179-219.
106
3. Blaser, R. E. , T. H. Taylor, W. Grlffeth, and W. H. Skrdla. 1956. Seed-
ling competition in establishing forage plants. Agron. J. 48:1-6.
4. Bryant, H. T. and R. E. Blaser. 1968. Effects of clipping compared to
grazing ladino clover-orchardgrass and alfalfa-orchardgrass mixtures.
Agron. J. 60:165-166.
5. Chamblee, D. S. and R. L. Loworn. 1953. The effect of rate and method
of seeding on the yield and botanical composition of alfalfa-orchardgrass
and alfalfa-tall fescue. Agron. J. 45:192-196.
6. Chippindale, H. G. 1949. Environment and germination in grass seeds.
J. Brit. Grassland Soc. 4:57-61.
7. Clay, R. E. and R. W. Allard. 1969. A comparison of the performance of
homogeneous and heterogeneous barley populations. Crop Sci. 9:407-412.
8. Donald, C. M. 1963. Competition among crop and pasture plants. Adv.
Agron. 15:1-118.
9. Fyfe, J. L. and H. H. Rogers. 1965. Effects of varying variety and
spacing on yields and composition of mixtures of lucerne and tall fescue.
J. Agric. Sci. 64:351-359.
10. Hamblin, J. and A. A. Rosielle. 1978. Effect of intergenotypic competi-
tion on genetic parameter estimation. Crop Sci. 18:51-54.
11. Hanley, F., R. H. Jarvis, and W. J. Ridgman. 1964. The effects of
nitrogenous manuring, inter-row distance and method of sowing on the
yields of a lucerne-cocksfoot ley. J. Agric. Sci. 62:425-431.
12. Jennings, P. R. and R. C. Aquino. 1968. Studies on competition in rice.
III. the mechanism of competition among phenotypes. Evolution 22:529-
542.
13. Jennings, P. R. and J. DeJesus. 1968. Studies on competition in rice.
I. competition in mixtures of varieties. Evolution 22:119-124.
14. Jensen, N. F. and W. T. Federer. 1964. Competing ability in wheat.
Crop Sci. 5:449-452.
15. Jones, M. B. and R. A. Evans. 1960. Botanical composition changes in
annual grassland as affected by fertilization and grazing. Agron. J.
52:459-461.
16. Knight, W. E. 1953. Breeding ladino clover for persistence. Agron. J.
45:28-31.
17. Rhodes, I. 1973. Relationship between canopy structure and productivity
in herbage grasses and its implications for plant breeding. Herbage
Abstr. 43:129-133.
18. Robinson, R. G. 1969. Annual legume-grass mixtures for forage and seed.
Agron. J. 61:759-761.
19. Rossiter, R. C. 1966. Ecology of the mediterranean annual-type pasture.
Adv. Agron. 18:1-56.
20. Sakai, K. 1955. Competition in plants and its relation to selection.
Cold Spring Harbor Symposia in Quantitative Biology 20:137-157.
21. Templeton, W. C. , Jr., T. H. Taylor, and J. R. Todd. 1965. Comparative
ecological and agronomic behavior of orchardgrass and tall fescue. Ken-
tucky Agric. Exp. Stn. Bull. 699.
22. Tewari, G. P. and A. R. Schmid. 1960. The production and botanical com-
position of alfalfa-grass combinations and the influence of the legume on
the associated grasses. Agron. J. 52:267-269.
107
PANEL DISCUSSION:
BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
PERENNIAL LEGUMES
By W. A. Cope
White clover is an important component of pasture in the USA wherever
soil fertility and moisture are adequate. Possibly fifty million acres of
pasture have varying amounts of white clover. Red clover and alfalfa are
increasingly being used in short term pasture rotations in the upper South.
White clover is used almost exclusively in mixture with grasses, while al-
falfa and red clover are used predominantly in pure stand for hay.
Basic Requirements of a Competitive Legume. Persistence of the legume in
mixture with grass is a major problem. The build-up of disease and insect
pests with extensive legume use seems to be the one most significant factor in
limiting persistence. However, the basic competitive ability of the legume
is important. The giant (ladino) white clover, introduced about three decades
ago, is more competitive with the robust pasture grasses than the small white
clovers. The term "pasture type" has long been used to distinguish legumes
with growth habit conducive to compatability with pasture grasses. Decumbent
and small growing types possibly are more tolerant to the selective grazing
to which legumes are subjected.
Growth Habit and Pasture Use. Forage legumes differ widely in growth
habit. White clover has almost unlimited potential for vegetative reproduction
by rooting of stolons. Red clover and alfalfa depend on maintenance of healthy
crowns for stand persistence. Birdsfoot trefoil and crownvetch are not ex-
tensively grown in the South, but provide examples of the interaction of
different growth types when grown with and without grass.
Traits associated with white clover's competitive ability with grasses
have been noted by several researchers (1, 5, 11, 12). Gibson (5) summarized
such traits with additions from his research:
1. Foliage density.
2. Amount and time of flowering.
3. Number and size of stolons.
4. Length of internodes.
5. Frequency of stolon branching.
In alfalfa the creeping rooted or broad crowned type has been exploited
to develop grazing varieties for semi -arid areas of North America. Hay types
of alfalfa may not vary enough in growth habit to differ significantly in
grazing performance. In the South alfalfa is used in mixtures with grass only
to a limited extent.
108
Phenotypic variation in red clover has not been extensively used to sel-
ect for competitive ability with grasses.
Crownvetch is strongly creeping rooted and where adapted could become an
important legume. It also varies greatly in stem size and uprightness; these
traits could be exploited for grazing.
Birdsfoot trefoil has "pasture types" that have long been recognized.
'Empire' is a naturalized selection from New York State preferred for its
survival under grazing. It is smaller and less upright than European
varieties .
Interactions: Pure Stand vs Mixed Stand. A number of studies relating
phenotype to pasture type have been made with white clover. Knight (10) ,
Dijkstra and de Vos (4), and Gibson et al. (5) noted a strong correlation
among genotypes for performance in pure stand and with grass. However, the
correlations were not perfect and thus the need for testing genotypes in
mixtures. Atwood and Garber (1) noted that the best sods were formed by
taller, more spreading, and more densely growing clones, but stated that
growth habit of individual spaced plants was not closely correlated with
performance in sod. Gibson et al. (.5) and Dean (3) each concluded that
"non-viney" types are superior in forage production to "viney" types. Gibson
(6) found very little difference in varietal ranking of forage production when
six white clover varieties were planted with and without grass (Table 1). For
individual clones of clover there may be a reversal of performance from pure
stand to mixed stand. However, for a variety comprised of many genotypes
such a reversal would not be expected.
In its area of primary adaptation alfalfa is often grown in mixture with
grass with increased total yield over pure stand. Such plantings may be
either mowed or grazed. In the upper South there is increasing interest in
sod seeding alfalfa in pasture. Hay types are used. In semi-arid areas
broad crowned "creeping" alfalfa is important for grazing. When such types
are compared to hay types in mixtures for grazing and in pure stand for hay
(SO there may be a sharp reversal in ranking for production and for stand
persistence (Table 2). Clearly, the broad crowned types are superior for
grazing.
'Penngift' crownvetch yields less (Table 3) under a hay regime than other
varieties (2) . However, under simulated pasture conditions (7_, <3) it is more
productive and persistent (Table 4). It differs from other varieties in that
stems are smaller and less upright.
'Empire' trefoil is more persistent under grazing than the more robust,
upright varieties which outyield Empire when managed for hay.
Conclusions . Hay types have been described for various forage legumes,
generally in terms of plant morphology. These traits appear to relate pri-
marily to potential for vegetative reproduction--regeneration of independent
plants or broadening of crowns. To a lesser extent they relate to tolerance
of selective grazing. At present it appears that legume breeders depend to a
large extent on selecting in pure stand for traits that contribute to good
109
Table 1.
Yield
grass
and rank of white
clover varieties grown
with and without
White clover
Wi thout
grass
With
grass
variety
Yield
Rank
Yield Rank
XPT-1
393
1
646
1
Ladino
373
2
596
2
Regal
368
3
596
3
Espanso
363
4
546
5
XPT-2
348
5
548
4
La. S-l
250
6
512
6
From
Gibson, Crop Sci„ 4:344
Table 2.
Stand of alfalfa varieties grazed
cut for hay in pure stand. Final
after five years
in mixture with bromegrass or
stand in percent of original
Final stand in percent of original
Alfalfa
variety
Crown
type
With brome
grazed
Pure stand
Hay
Exp. 37
b
105
111
Nomad
b , n
77
106
Rhizoma
b
77
102
Rambler
b , cr
100
90
Buffalo
n
15
100
Grimm
n
16
100
Ranger
n
21
100
Vernal
b
42
104
From
Kehr ,
Conard, Alexander,
and Owen,
Neb.
Agr. Exp. Sta. Res. Bull.
211, 1963.
110
Table 3. Forage yield of
Carolina
three crownvetch varieties at Raleigh,
North
Yield, tons p
er acre
Crownvetch
One cut,
Three cuts,
variety
1967
1968
Emerald
0.88
3.99
Chemung
0.87
3.94
Penngif t
0.63
2.73
Table 4. Survival of crownvetch
week intervals for six
varieties
years
grown with
fescue and cut at two
Crownvetch
variety
5 cm
Stubble ht.
10 cm
Penngif t
78
M-2
— crowns M
68
Chemung
51
74
Emerald
10
4
From Hart, Thompson, Hungerford, Agron. J. 69:287.
Ill
performance in mixture with grass. Studies on the performance of single geno-
types and mixtures of genotypes (e.g., the synthetic variety) when grown both
alone and with grass are not very common.
Presently forage legume breeders are faced with the very pressing prob-
lem of developing pest resistance. When such problems diminish, greater
attention can be given to performance of genotypes in mixtures with grass.
REFERENCES
1. Atwood, S. S. , and R. J. Garber. 1942. The evaluation of individual
plants of white clover for yielding ability in association with
bluegrass. J. Am.„ Soc. Agron. 34:1-6.
2.
Cope, W. A.
1968.
Unpublished
Annual
Project Report.
3.
Dean, C. E.
1975.
Evaluation
of two
plant types in white clover (T.
repens) and changes in plant type brought about by natural
crossing. Soil and Crop Sci. Soc. Fla., Proceedings. 34:111-113.
4. Dijkstra, J. , and A. L. F. de Vos. 1972. The evaluation of selections
of white clover (Trifolium repens) in monoculture and in mixture
with grass. Euphytica 21:432-449.
5. Gibson, P. B. , G. Beinhart, J. E. Halpin, and E. A. Hollowell. 1963.
Selection and evaluation of white clover clones. I. Basis for
selection and a comparison of two methods of propagation for
advanced evaluations. Crop Sci. 3:83-86.
6. Gibson, P. B. 1964. A technique requiring few seed for evaluating
white clover strains. Crop Sci. 4:344-345.
7. Hart, R. H. , and A. J. Thompson, III, and W. E. Hungerford. 1977.
Crownvetch-grass mixtures under frequent cutting: Yields and
nitrogen equivalent values of crownvetch cultivars. Agron. J.
69:287-290.
8. Henson, P. R. , L. A. Tayman, and G. E. Carlson. 1968. Performance of
crownvetch varieties and clones under severe defoliation. Second
Crownvetch Symposium, The Penn. State Univ. Agron. Mimeo 6:129.
9. Kehr, W. R. , E. C. Conard, M. A. Alexander, and F. G. Owen. 1963.
Nebraska Agr. Exp. Sta. Res. Bull. 211.
10. Knight, W. E. 1953. Breeding ladino clover for persistence. Agron.
J. 45:28-31.
11. Knight, W. E. 1953. Interrelationships of some morphological and physio-
logical characteristics of ladino clover. Agron. J. 45:197-199.
12. Ronningen, T. S. 1953. Susceptibility to winter injury and some other
characteristics in ladino and common white clovers. Agron. J.
45:114-117.
112
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
BREEDING PERENNIAL GRASSES FOR GRASS-LEGUME MIXTURES
By R. L. Haaland and C. S. Hoveland
Of the many grass species grown in the United States, three cool-season
species (tall fescue, orchardgrass , and Kentucky bluegrass) and three warm-
season species (bahiagrass, bermudagrass , and dallisgrass) are major contri-
butors to the forage economy of the Southeast. The cool-season species,
especially tall fescue, predominate in the Upper South (KY, TN, VA, and NC)
while the warm season species are most important in the coastal plains area.
In the Upper South up to one third of the pastures contain adequate legumes but
in the Lower South legumes make little or no contribution to pasture produc-
tion.
There are several reasons why perennial grass-legume mixtures are scarce
in the Deep South.
PROBLEMS
1. More compatible grasses such as bluegrass and orchardgrass do not persist
in the Coastal Plains.
2. Warm-season grass species usually form very dense sods and are extremely
competitive.
3. The combination of heat stress and multiple pathogen complex severely
limit the persistence of cool-season grass and legumes in the Deep South.
4. The warm-season grasses are more tolerant than legumes to the pathogen
load, heat load, and periodic droughts.
5. The positive energetics of carbon fixation of warm-season grasses and
the negative energetics of N2 fixation in legumes gives the warm-season
grasses a competitive advantage.
6. The grasses can usually withstand overgrazing better than the legumes.
7. Grazing animals will often selectively graze legumes leaving the grasses
to become more competitive.
8. Growing periods of the grasses and legumes often do not nic.
9. Grasses may grow up and over clover when forage is allowed to accumulate.
10. Grasses will tolerate lower soil pH, P and K thus giving them a competitive
advantage over legumes.
Proposed advantages of the grass component of grass legume mixtures have
been discussed for many years. They include:
1. The grass component, in addition to supplying nutrition, results in a pad
for firm footing.
2. The fibrous nature of grass roots improves water penetration and percola-
tion in the soil.
3. Grasses in a mixed sward will reduce bloat potential.
113
SELECTION CRITERIA AND TESTING
Grass-legume mixtures have been evaluated for years and many management
systems have been developed. Little work has been done on developing selection
criteria in grasses to make them more compatible with legumes. Grasses and
legumes compete in a mixed sward for light, water, minerals, and space. En-
virnomental factors limiting both grass and legumes are pathogen load, heat
load and drought. There are many ways breeders might enhance grass compati-
bility with legumes. For example, more upright leaves would decrease compe-
tition for light, pathogen resistance would increase drought tolerance, less
luxury consumption of K+ would be beneficial to legumes, less dense sod (less
tillering) will decrease space requirements for grass and increase amount of
space available to legumes.
For progress to be made in developing grasses that are compatible with
legumes the grass breeder must make the following commitments:
1. Define objectives associated with compatibility
2. Work in close association with legume breeders
3. Work in close association with forage managers
4. Be innovative
114
PANEL DISCUSSION: BREEDING GRASSES AND LEGUMES FOR USE IN MIXTURES
BREEDING FORAGES FOR USE IN MIXTURES WEST OF THE MISSISSIPPI
By Ethan C. Holt
While there are hundreds of native and introduced grasses being used for
forage in the western portion of the region, breeding programs and/or improved
or tame pasture use are limited to relatively few species. Examples of th-ese
are: Grasses- Klein, buffel, bermuda, weeping love, old world bluestem,
switch, dallis, tall fesue; Legumes- alfalfa, white clover, arrowleaf clover,
subterranean clover, sweet clover, crownvetch and vetch.
As the environment (climatic and edaphic factors) becomes less favorable
for plant growth and survival, increasing emphasis in plant improvement pro-
grams is placed on adaptation, longevity, stand establishment, seasonal growth
pattern and forage yield and quality in monoculture. Since essentially no per-
ennial pasture legumes have been developed for the area, no emphasis has been
placed on selection criteria for developing forage plants for compatibility in
mixtures .
There are opportunities and needs for forage plant mixtures in the area
which may consist of perennial grass - annual legumes, perennial grasses and
legumes and mixtures of perennial grass species. Problems of such mixtures in-
clude:
1. Very few adapted, domesticated legumes.
2. Alkaline soils leading to minor element deficiencies (esp. iron)
in many leguminous species and also in grasses.
3. Cotton root rot in many of the central prairie soils, essentially
eliminating tap rooted legume species.
4. Long periods of drouth, winter or summer, to which warm-season
grasses are better adapted than legumes.
5. Differences in palatability between species which lead to selec-
tive grazing pressure on the more palatable component of the
mixture.
6. Different components of the mixture may require establishment at
different seasons, with the additional moisture, light and nutri-
ent stress as contributed by the competing component.
7. Growing periods of components of mixture may not be the same
which may be a problem but also may offer advantages.
Advantages of grass-legume mixtures have been discussed by others. There
may be advantages to mixtures of grasses, not necessarily the same advantages
as for grass-legume mixtures, but with potential needs for screening procedures
for compatibility of such mixtures. Among the advantages usually listed are:
1’. Reduce establishment period prior to utilization.
2. Lengthen grazing period and stabilize production.
3. Improve forage quality through opportunity for selective grazing.
115
4. Better animal performance.
The growth and maintenance of species in mixtures may involve several lev-
els and sources of competition and interacting factors, such as:
1. Moisture and nutrients, including deficiences of both.
2. Physical space, light, temperature, C02.
3. Plant-animal interface including palatability , grazing selectiv-
ity.
4. Plant response to defoliation.
In the Western portion of the Southern Region, the normal rainfall pattern
results in both summer and winter moisture stress periods and the possibility
of drouth stress at any time of the year. Summer drouth limits the production
of tropical legumes throughout the area and winter temperatures result in win-
terkill except for a small area in South Texas. Except for alfalfa, perennial
temperate legumes are limited by summer drouth. The establishment and winter
growth of both perennial and annual temperate species are frequently limited by
erratic fall rainfall and winter moisture stress periods. Calcareous soils
with limited iron availability frequently result in iron chlorosis in legume
species. Thus the first objective in legume breeding programs is adaptation
and survival rather than compatibility of legume-grass mixtures.
The environmental limitations described above suggest primarily the use
of annual temperate legumes in conjunction with either annual temperate or per-
ennial tropical grasses. The development and use of temperate annual legume-
grass mixtures have not encountered any serious compatibility limitations.
However, differences in seedling vigor, rate of growth, response to low temper-
ature, length of growing season and response to defoliation are factors which
require attention as greater specificity in mixtures and site adaptations de-
velop .
Temperate annual legume-tropical perennial grass associations present nu-
merous compatibility and competition problems requiring solution. These prob-
lems are intensified by the extremes in environment encountered in the western
area. Fall establishment of the temperate legume is hampered by competition of
the perennial grass for space, moisture, nutrients and light. Bunch grasses
and open-sod grasses compete less for space and light. Do we breed grasses for
these characteristics and for reduced fall growth? Legumes with increased
seedling vigor and high temperature tolerance in the seedling stage would seem
to be necessary objectives.
T-emperate annual legumes are the most competitive for light, moisture and
nutrients at the time tropical grasses initiate spring growth. One option
would be to develop early maturing legumes or types with open growth to permit
initiation of grass growth in the spring. An early maturing legume would make
no contribution to the forage quality problem encountered in late spring and
summer with tropical grasses. On the other hand, an objective of late legume
maturity may not be compatible with maximum summer forage production under con-
ditions of summer drouth. The type of cattle program may influence the type of
legume growth pattern required for specific situations.
Grass mixtures are used in the drier areas and these present compatibility
problems. Differences in drouth tolerance, earliness, response to defoliation
and palatability influence performance and persistence under grazing.
Numerous factors affecting the relationships between or among species
116
grown in association have been enumerated by individuals on the panel. If
breeding programs are to be effective in selecting for mixture compatibility,
problems with specific mixtures must be delineated and programs with both or
all the species in the mixture coordinated. The question is raised as to
whether plant breeding programs in general are sufficiently advanced, refined
and coordinated for breeding for specific compatibilities. It would seem nec-
essary to test breeding materials in plant associations if the final product is
to be used in mixtures and preferably under grazing.
The development of selection indices for compatibility factors which in
turn are influenced by utilization or management factors imposed simultaneously
will be difficult. Some of the compatibility problems may be more easily
solved by management, especially in situations where intensive management is
practical .
117
I
SCLEROTINXA CROWN AND STEM ROT OF ALFALFA IN NORTH CAROLINA
By Ronald E. Welty and Thad H. Busblce
The earliest report of Sclerotinia crown and stem rot as a disease of
legumes was in Germany in 1857 (8). The fungus was described, a partial host
range, and some control data were published in 1872 (18), but alfalfa was not
included as a host until 1915 (10). The disease cycle was described in 1917
(9) and 1919 (23), but it was not until 1965 (22) that the biology of the
pathogen was carefully studied and described. The pathogen is widely dis-
tributed on forage legumes, but damage to alfalfa is usually less severe than
on Trifolium spp., especially crimson and red clovers. Disease losses occur
mainly during cool, humid seasons in the southeastern, northeastern, and
western United States, and in Britain, Canada, Germany, Norway, and Sweden.
The severity of the disease varies from season to season and is often
scattered within plantings. Losses may involve entire fields or areas as
small as 1-2 cm in diameter. Although plants of all ages are susceptible,
the incidence and severity of the disease is greatest in seedlings.
Causal Organism
The binomial proposed by Eriksson (8), Sclerotinia trifoliorum Eriks.,
is in wide usage today. According to the Sclerotinia species concept of
Purdy (17), the crown and stem rot pathogen is Sclerotinia sclerotiorum (Lib.)
d By. (Syn. S_, trifoliorum Erik.). Korf and Dumont (14) proposed the new
generic name Whetzelinia to replace that portion of the genus which included
Sclerotinia sclerotiorum. In this presentation, the synonym _S . trifoliorum
will be used to designate the causal agent of the disease of alfalfa, and other
forage legumes.
In North Carolina, apothecia usually develop from sclerotia during cool,
wet weather in October and November. Ascospores are carried by wind to
leaves and stems and infection occurs when ascospores germinate and penetrate
the host directly. Throughout the winter and spring, if high moisture and
cool temperatures prevail, secondary infection occurs as mycelium spreads to
other leaves and stems. When the food supply is exhausted or environmental
conditions are unsuitable for continued growth, the fungus produces hard,
black sclerotia on or in stem and crown tissues which remain in soil or on
the soil surface. Sclerotia formed in the spring lie dormant during the
summer. In the fall sclerotia produce one to several apothecia which contain
asci and ascospores. It is generally accepted that mycelium grows only to a
limited extent in soil and new plant infections are rarely initiated by
mycelium from sclerotia (22).
The effect of temperature on growth and pathogenicity of S^. trifoliorum
has been well documented (15) . The optimum temperature for growth in culture
is 15-16 C; the fungus grows between -2 and 27 C and is killed at -24 and
118
42 C. The effect of relative humidity or free water on infection of alfalfa
by J5. trifolio rum has not been studied, but Abawi and Grogan (1) concluded for
_§_• sclerotiorum on snap beans that free water for 48—72 hours is required by
ascospores for infection and lesion development in beans. Further development
of the disease is stopped if the inoculated tissue becomes dry. The same is
likely true for alfalfa.
The host range of _S. trif oliorum is limited largely to forage legumes
and there appears to be little host specificity for isolates. In the green-
house, isolates of S^. trif oliorum from crownvetch and alfalfa are capable of
attacking either host (4); in field studies (3), isolates of _S. trif oliorum
from alfalfa, red clover (Trifolium pratense) , and crown vetch (Coronilla
varia) are equally pathogenic on these same hosts regardless of isolate
source, trif oliorum can infect alfalfa, red clover, Ladino clover (T.
repens) , and crown vetch. Common hosts for sclerotiorum do not appear to
be natural hosts for S_. trif oliorum, however, seedlings of lettuce (Lactuca
sativa) , tomato (Lycopersicon esculentum) , snap beans (Phaseolus vulgaris)
and soybeans (Glycine max) can be infected in the greenhouse when favorable
conditions are provided for disease development.
The disease can be partly controlled by deep plowing to bury the
sclerotia, planting sclerotia-free seed, and maintaining 3-4 year rotations
between forage legumes (21, 22). Penta- and tetrachloronitrobenzene (19, 23)
and benomyl (13) have been applied to red clover to control crown and stem
rot, but the cost of application does not appear to be economical, except
perhaps in fields used for seed production. In this study, we applied single
and multiple applications of benomyl to alfalfa to evaluate disease control
and to better understand the disease cycle. Since it is known that some
alfalfa and clover plants or cultivars sustain less Sclerotinia crown and stem
rot damage than others (2, 5, 6, 7, 11, 12, 16, 20), but resistance of
economic importance is not available (7), we made field evaluations of disease
damage in field plants of selected alfalfa cultivars and breeding lines.
Benomyl application. — ’Team* alfalfa was broadcast seeded on 16 September
1974 on a farm near Raleigh, N. C. After the stand was established, plots
1.5 m x 3 m (5 x 10 ft) were delineated by applying a contact herbicide in
5 cm strips. Six replications of 15 plots were prepared with a 1.5 m border
surrounding the experiment. Treatments were assigned to plots in a randomized
block design and benomyl at 560 g/935 1/ha active ingredient (0.5 lb/100
gal/A) was applied at 17.2 k Pa (25 psi) once, twice, or monthly. Spray
dates were between the 14th and 17th day of each month beginning with October
and ending with February. Crown and stem rot damage was determined by
counting and measuring or estimating the size of the affected areas as they
became visible in each plot. Since 6 plots in each replication were scheduled
for spraying during the spring and summer months, but had not yet been sprayed
when the disease ratings were made, they were included in the analysis as
multiple observations of the nonsprayed controls. Arcsin transformation of
the percent damage was used to stabilize the error variance in statistical
analysis. To determine the influence of monthly sprays on crown and stem rot
damage, the means from the nonsprayed controls were compared with the means
from plots sprayed once (October, November, December, January, and February),
twice (October + December, October + January, and October + February) or
monthly (October through February) . The F values were used to evaluate the
119
TABLE 1. — Incidence of Sclerotinia crown and stem rot after applications of benomyl to fall seeded
alfalfa
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4/ Multiple check is the average of six non-sprayed plots
differences between nonsprayed and sprayed plots at P = 0.05 (*) and 0.01 (**) .
The data in Table 1 are the number of areas and the percent crown and stem
rot damage in the plots. The percentages were transformed from the arcsin
after the analysis.
When symptoms of crown and stem rot were first observed 16 January
1975, damaged areas were 1-2 cm in diameter, and their number and location
among plots and replications were highly variable. Subsequent inspections
at 3 to 7 day intervals between 16 January and 11 February revealed that
the number of circular diseased areas had increased and by mid-February their
diameters had increased to 6-8 cm. Subsequently, the size of the diseased
area per plot was measured or estimated and converted to a percentage of the
plot. The appearance of sclerotia confirmed the damage to have been caused
by S. trif oliorum. By the end of March and early April, warm temperatures
and long dry periods made conditions more favorable for the host than for the
pathogen and regrowth began from nondiseased crown buds.
Significant differences were noted among treatments. The most effective
spray schedule was monthly; the most effective single spray was December,
followed closely by November; the most effective time for double spray was
October + December. Benomyl applied after disease symptoms were observed
(Jan. 16) did not reduce further development of damage. In this study,
December was apparently a key month to spray for disease control. The
relatively high damage on 12 February in plots sprayed in October 4- February
may perhaps be an experimental anomaly because one plot had 60% damage, while
the remaining 5 plots averaged 7% damage.
Applications of benomyl before symptoms appeared suppressed the severity
of crown and stem rot, but applications after symptoms appeared did little to
retard the spread of the disease. Benomyl probably controlled primary
(ascospores) but not secondary (mycelium) infection. We did not establish
that a single application of benomyl in December can be regularly applied to
seedling alfalfa to prevent crown and stem rot, but one or two applications
when apothecia are present might give economical control.
Germplasm evaluations. — Alfalfa germplasm developed in several different
geographic locations were evaluated by establishing plots in the fall of
1973, 1974, and 1977 in a randomized block design near Raleigh, N. C. The
fields were fertilized according to soil test and state recommendations and
seeded at 22.4 kg/ha (20 lbs/A). The plots were three drilled rows, 0.76 x
4.57 m, with 22.8 cm between rows and 30.6 cm between plots. The first culti-
var test contained five replications of 17 entries; the second cultivar test
contained six replications of 23 entries; and the third cultivar test con-
tained six replications of 30 entries. Nine entries were common to the three
tests (Table 2). For statistical analysis the square root transformation of
the percentage of disease damage was used for test 1 and 2.
After crown and stem rot had been identified, the length of the damaged
area was measured in each of the three rows of each cultivar on 8 March 1974
in test one, on 28 March 1975 in test two, and on 15 March 1978 in test
three. The amount of damage is expressed as a percentage of the plot. Dis-
eased stems were either cultured or incubated and the development of sclerotia
in the stem tissue confirmed the presence of J3. trif oliorum. Closely related
121
TABLE 2. — The amount of Sclerotinia crown and stem rot in several alfalfa
cultlvars measured in March in three replicated field experiments
Percentage
of plot damaged by
Sclerotinia
Entry
1974
1975
1978
Liberty (Syn 1)
0.2
8.4
13.4
Liberty (Syn 2)
0.7
8.5
5.4
Arc
2.3
6.8
5.7
Team
1.0
7.7
10.2
NCMP 2 (b Syn 1)
0.7
3.3
10.7
NCW 21 (a Syn 1)
0.5
8.9
13.5
Williamsburg
3.2
9.2
12.9
Weevlchek
2.8
13.2
19.8
Kanza
5.7
19.5
21.6
Apalachee
1.1
3.1
-
Victoria
3.9
29.5
—
LSD 0.05
2.87
6.51
10.85
CV (%)
54
31
75
entries are grouped to show similarities in disease incidence. The cultivars
tested included the most advanced breeding material in the North Carolina
germplasm collection and some were more tolerant to crown and stem rot than
others.
To determine whether the apparent tolerance observed in the field could
be shown in the greenhouse, 14-day-old seedlings of Apalachee and Victoria,
cultivars with the widest range in disease tolerance in 1974 and 1975 (Table
2) , were inoculated with oat grains infested with JS. trif oliorum. Tolerance
was not demonstrated because all plants died from the disease.
The development of cultivars of forage legumes that are tolerant or
resistant to J3. trif oliorum has been difficult because of the nonspecific
character of the pathogen, the lack of a form of resistance easily identified
by plant breeders, and an inability to create consistently, in greenhouse and
field experiments, epidemics that are similar to those in nature. The nature
of the tolerance observed was not determined, but the study does indicate that
germplasm adapted to the southeast has morphological or physiological
characters that are absent in varieties selected elsewhere. Perhaps
tolerance is related to individual plant vigor, as reported for Ladino
clover (11) .
122
LITERATURE CITED
1. Abawi, G. S., and R. G. Grogan. 1975. Source of primary inoculum and
effects of temperature and moisture on infection of bean by
Whetzelinia sclerotiorum. Phytopathology 65:300-309.
2. Allison, J. L. , and C. H. Hanson. 1961. Methods for determining patho-
genicity of Sclerotinia trifoliorum on alfalfa and Rhizoctonia solani
on Lotus. Phytopathology 41:1 (Abstr.).
3. Cappellini, R. A. 1960. Field inoculations of forage legumes and
temperature studies with isolates of Sclerotinia trifoliorum and
Sclerotinia sclerotiorum. Plant Dis. Reptr. 44:862-864.
4. Carroll, R. B., F. L. Lukezic, and J. M. Skelly. 1970. Evidence iso-
lates of Sclerotinia trifoliorum from crownvetch and alfalfa are not
specific for either host. Plant Dis. Reptr. 54:811-814.
5. Cormack, M. W. 1942. Varietal resistance of alfalfa and sweet clover
to root- and crown-rotting fungi in Alberta. Sci. Agric. 22:775-786.
6. Elgin, J. H., and E. H. Beyer. 1968. Evaluation of selected alfalfa
clones for resistance to Sclerotinia trifoliorum Erikss. Crop Sci.
8:265-266.
7. Elliot, E. S., R. E. Baldwin, and R. G. Carroll. 1969. Root rots of
alfalfa and red clover. West Virginia Agr. Exp. Stn. Bull. 585T.
32 p.
8. Eriksson, J. 1880. Om klofverotan med sarskilt afseende pa dess
upptradande ivart fadernesland aren 1878-1879. Kongl. Svensk
Landtbr. Akad. Handl. och. Tidsskr. Nr. 1 1880 (Abstract in Bot.
Centbl. 1:296).
9. Gilbert, A. H., and C. W. Bennett. 1917. Sclerotinia trifoliorum,
the cause of stem rot of clovers and alfalfa. Phytopathology 7:432-
442.
10. Gilbert, A. H. , and D. S. Myer. 1915. Stem rot of clovers and alfalfa
as a cause of clover sickness. Kentucky Agr. Exp. Stn. Circ. 8:46-60.
11. Hanson, A. A., and J. H. Graham. 1955. A comparison of greenhouse and
field inoculation of ladino clover with Sclerotinia trifoliorum.
Agron. J. 47:280-281,
12. Hanson, A. A., J. H. Graham, and K. W. Kreitlow. 1953. The isolation
of ladino clover plants resistant to Sclerotinia trifoliorum.
13. Jenkyn, J. F. 1975. The effect of benomyl sprays on Sclerotinia
trifoliorum and yield of red clover. Ann. Appl. Biol. 81:419-423.
14. Korf, R. P. and K. P. Dumont. 1972. Whetzelinia, a new generic name
for Sclerotinia sclerotiorum and _S . tuberosa. Mycologia 64:248-251.
15. Kreitlow, K. W. , and V. G. Sprague. 1951. Effect of temperature on
growth and pathogenicity of Sclerotinia trifoliorum. Phytopathology
41:752-757.
16. Niemann, E. 1962. Testing red and white clover for rot resistance.
NachrBL. PflSch Dienst., Stuttgart. 14:5-9.
17. Purdy, L. H. 1955. A broader concept of the species Sclerotinia
sclerotiorum based on variability. Phytopathology 45:421-427.
18. Rehm, Emil. 1872. Die Entwicklungsgeschichte eines die Kleearten
zerstorenden (Peziza ciborioides) ♦ Journ. Landw. 20:151-178.
123
19.
Sundheim, L. 1973. Control of the clover rot fungus and residues in
red clover hay following fall application of quintozen. Norwegian
Plant Protection Institute, Vollebekk, Norway, pp. 331-335.
[Abstract in Review of Plant Pathology 52:422],
20. Valleau, W. D. , E. Y. Fergus, and L. Henson. 1933. Resistance of red
clover to Sclerotinia trifoliorum Erikss., and infection studies.
Kentucky Agr. Expt. Stn. Bull. 341.
21. Wells, J. C., and R. T. Sherwood. 1961. Save forages from disease.
N. C. State Univ. Ext. Circ. No. 361.
22. Williams, G. H., and J. H. Western. 1965. The biology of Sclerotinia
trifoliorum Erikss. and other species of sclerotiorum-f orming fungi.
Ann. Appl. Biol. 56:253-260.
23. Wolf, F. A., and R. 0. Cromwell. 1919. Clover stem rot. North Carolina
Agr. Expt. Sta. Tech. Bull. 16.
24. Ylimaki, A. A. 1955. On the effectiveness of penta- and tetrachloro-
nitrogenzenes on clover rot (Sclerotinia trifoliorum Erikss.).
Acta Agralia Fennica 83:147-158.
124
BREEDING FOR PEST RESISTANCE IN RED CLOVER
By N. L. Taylor and R. R. Smith
Red clover ( Trifolium pratense L.) generally has been protected from
pests by the use of resistant cultivars. Consequently, much breeding research
has been directed by this approach to develop disease resistance and indirect-
ly, to improve yield, quality and longevity. It is the purpose of this paper
to examine progress that has been made particularly in the last two decades.
Problems and opportunities for further breeding will be elucidated.
RESISTANCE TO DISEASES
Southern Anthracnose
One of the first diseases of red clover for which resistance was obtained
was southern anthracnose caused by Colletotrichum trifolii B. & E. This dis-
ease occurs in the warmer regions of North America, Kenya and South Africa.
Lesions occur on leaves, stems and crowns, causing a typical "shepherd's
crook" of the petioles, and eventually resulting in the death of the infected
host. Resistance to one race of the fungus is conditioned by one dominant
gene according to Athow and Davis (1957). However, genetic studies of resis-
tance are generally lacking. Cultivars which carry resistance to the fungus
include 'Kenland' and 'Kenstar'. Perhaps as a result of the use of resistant
cultivars, southern anthracnose ephiphy totics have not been observed for sev-
eral years, at least in Kentucky.
Northern Anthracnose
Northern anthracnose caused by Kabatiella caulivora (Kirch.) Karak. has
symptoms similar to southern anthracnose except that death of plants usually
does not occur directly. The disease is restricted to the cooler sections of
North America, Europe and Asia. In recent cool years, the disease has occured
in the United States at least as far south as Kentucky. Resistance to the
fungus was determined by Smith and Maxwell (1973) to be dominant and controlled
by more than three genes. Sakuma et al. (1973) found the resistance was de-
termined by the complementary action of two dominant genes. Resistant culti-
vars include 'Lakeland' and 'Arlington'. Some of the Northern United States
and Canadian cultivars such as 'Altaswede' have a fairly high level of resis-
tance, apparently naturally selected under field conditions over a long period.
In Europe, some of the tetraploid cultivars have been reported to possess a
higher level of resistance than comparable diploids.
125
Powdery Mildew
Powdery mildew caused by Erysiphe polygon! DC is another disease of red
clover which is controlled by using the resistant cultivars ’Arlington* , 'Lake-
land', ’Orbit’ and ’Tensas’. The disease is prevalent wherever red clover is
grown. The growth of mycelium and powdery appearance of condia give a conspic-
uous white or light-gray cast to the leaves which if infection is severe, turn
yellow to brown. Quality of foliage is apparently decreased, but no evidence
on yield has been obtained. Resistance is dominant in all clones tested, and
for five races, resistance was monogenic. For two other races, resistance
seemed to be controlled by two genes, and for another race, resistance was
inherited in a different manner in different clones. Twelve races of E. poly-
goni have been identified (Hanson, 1966; Stavely and Hanson, 1967).
Rust
Rust, caused by Uromyces trifolii var fallens produces pustules on leaves,
stems and petioles. When infection is severe, pustules are larger and more
numerous, causing death and loss of leaves. Rust occurs widely throughout the
humid and semi-humid regions of the world primarily in late summer or early
autumn. No resistant cultivars are available although breeding for resistance
is underway at the Wisconsin station (Engelke, et al. 1975). Sherwood (1957)
found 14 plants from 34 cultivars which were resistant to five races of the
fungus. Inheritance of resistance was determined by Diachun and Henson (1974a)
to be controlled by a single dominant gene. This source of resistance could
not be used for cultivar development, however, because it was linked with a
seedling lethality factor (Engelke, 1977). Engelke et al. (1975) found that
resistance to leaf rust was quantitatively controlled in crosses of some red
clover clones.
Targetspot
Several other leaf diseases occur on red clover, probably the most impor-
tant of which is Stemphylium leafspot or targetspot caused by Stemphylium
saroinae forme (Cav.) Wiltshire. It occurs in most humid regions of the world.
Lesions on the leaves, stems, and petioles at first are small, irregular dark
brown and sunken but later develop into large irregular, dark brown, sunken
spots. Several sources of resistance have been isolated (Kilpatrick, 1964;
Braverman, 1971) but the inheritance has not been investigated. Methods of
screening populations for resistance have been developed at the Wisconsin
Station and breeding of a resistant cultivar is underway (Murray et al. 1976).
Crown Rot
A very serious disease of red clover which results in death of plants and
often complete loss of stands is crown rot caused by Sclerotina trifoliorum
Erikss. The disease is widespread but apparently is more severe in regions of
Europe that have mild winters and heavy snows. In the United States the dis-
ease is most prevalent in the southern clover belt including Virginia, Kentucky
and Tennessee. Infection first occurs in late autumn when brown spots appear
on leaves which drop off and are overrun by white mycelial growth. Infection
in the spring results in a soft rot, often under snow cover, resulting in a
126
dead plant apparent by the time the snow melts or shortly thereafter. Black
sclerotia, the resting stage of the fungus, may be found around the base of
dead plants. Resistance, but not immunity has been discovered in red clover
collected in North Africa (Bond and Toynbee-Clarke, 1967). No reliable seed-
ling selection technique exists, according to Dixon (1975) but Verstad (1960)
used a cold frame technique to inoculate seedlings. Inheritance of resistance
has apparently not been investigated but is probably quantitative. In field
screenings 19 cultivars have been identified as resistant (Dixon and Doodson,
1974). Weibull ’ s ' Britta' is a Swedish crown-rot resistant cultivar (Ludin
and Jonnson, 1974). In the United States the cultivar Kenland is reputed to
possess a slight degree of field resistance. Autotetraploid cultivars are
more resistant to crown rot than comparable diploids according to Verstad
(1960). This test was based on chimera plants, i.e. plants with both tetra-
ploid and diploid shoots which were separated clonally and increased to form
tetraploid and diploids synthetics. In two cold frame experiments, tetraploids
averaged 67 and diploids 54 percent survival 71 to 76 days after inoculation.
The effect of induced tetraploidy differed by genotype suggesting that dosage
effects of genes for resistance may be important.
Virus Diseases
Virus diseases are prevalent wherever red clover is grown. The importance
of virus in reducing stands and yields is difficult to determine. The most
prevalent virus in Kentucky was bean yellow mosaic virus (BYMV) , followed by
peanut stunt virus (PSV) , white clover mosaic virus (WCMV), and tobacco ring-
spot virus (TRSV) in which were present in 76, 14, 10 and 0.54% of the infected
plants examined (Jones and Diachun, 1976). In Wisconsin, BYMV, Wisconsin pea
streak virus (WPSV), red clover vein mosaic virus (RCVMV), pea common mosaic
virus (PCMV), and alfalfa mosaic virus (AMV) were isolated from 48, 41, 34, 13,
and 6% respectively of 187 naturally infected plants. Thirty-nine percent had
two viruses, and two percent had three viruses (Stuteville and Hanson 1965).
In Sweden, the most prevalent viruses are red clover mosaic virus (RCMV) and
red clover necrotic mosaic virus (RCNMV) (Gerhardson and Lindsten, 1937).
Another common virus in Sweden is clover mild mosaic virus (CMMV) (Gerharson,
1977) . Viruses are transmitted by Acyrthosiphum pisum and Myzus persicae and
probably many other species of aphids (Gerharson, 1977). Symptoms of virus
vary greatly among clover genotypes within, and among viruses so that cross
inoculation and serological tests are necessary for identification. Infected
plants may be reduced in vigor to such an extent that death results. Clones
are particularly difficult to maintain because of increased opportunity for
infection. However, techniques for freeing clones of viruses by meristem
tissue culture appear promising (unpublished data, G. Phillips and G. B. Col-
lins, Univ. of Ky) . BYMV had no effect on digestibility of clover but increased
nitrogen concentration, and decreased chlorophyll concentration and forage
yield (Smith and Maxwell, 1971).
Resistance to BYMV, PCMV, and RCVMV was found among breeding lines and
cultivars by Stuteville and Hanson (1964). The only reports of inheritance
of virus resistance are those of Diachun and Henson (1974b). Clones were
selected from the cultivar Kenland which exhibited three types of reaction to
BYMV race 204-1: Necrotic local lesion (hypersensitive) reaction inherited as
a single dominant gene; resistance to mottling and systemic necrosis inherited
as a dominant gene; and a third reaction resistant to mottling again controlled
127
by a dominant gene which appears to be epistatic to the hypersensitive reac-
tion. No resistant cultivars have been developed although Kenstar and Arling-
ton are reported to have moderate field resistance to BYMV (Taylor and Anderson,
1973; Smith, et al. 1973). At the Kentucky station, research is under way to
transfer the hypersensitive reaction to BYMV race 204-1, by backcrossing to
the 10 clones of Kenstar.
Resistance to Insects
Published reports of resistance to nine insects (Table 1) include leaf-
hoppers, (Enpoasoa) aphids, weevils (Hyp era) , the clover root borer (Hytastinus)
and Apion spp. As pointed out by Manglitz and Gorz (1972), with the exception
of aphids, resistance has occurred largely by chance, probably as a result of
natural selection under field conditions. Resistance to the potato leafhopper
(Empoasoa fabae) is thought to have resulted from natural selection for pubes-
cence (Pieters, 1928). However, it is doubtful that the hairiness of American
red clover resulted entirely from selection by the leafhopper in view of the
known function of pubescence as a mechanism for high temperature tolerance.
Resistance to clover leaf weevil (Hypera punctata ) was greater in the Northern
United States and Canadian cultivars. Lakeland, Dollard and LaSalle than in
the Southern United States cultivars, Kenstar, Chesapeake, Kenland, and Penn-
scott (Gorz, et al. 1975). Resistance to the alfalfa weevil (H. postica)
apparently occurs in most red clover cultivars (Keller, et al. 1970). Bud
volatiles of red clover did not attract the clover head weevil (H. metes) as
much as those of other clover species (Smith, et al. 1976) although in leaf
disc feeding trials, red clover was apparently preferred over four clover
species (Smith, et al. 1975). The cultivars 'Manhardy', 'Otten', and 'Alta-
swede' had moderate levels of resistance to the clover root borer (Hytastinus
obscurus) in New York (Gyrisco and Marshall, 1960). Several lines of red
clover were found to be slightly resistant to flower weevils (apion spp)
(Perju, 1971). 'Dollard ' red clover is described as resistant to the pea aphid
Table 1. Published reports of resistance to insects
Name
Common
Scientific
Reference
Potato leafhopper
Pea aphid
Empoasoa fabae (Harris)
Acyrthosiphum pisum (Harris)
Pieters, 1928
Markkula, 1970
Wilcoxson, 1960
Yellow clover aphid
Clover aphid
Clover leaf weevil
Alfalfa weevil
Clover head weevil
Clover root borer
Clover flower weevils
Therioaphis tvifotii (Monell)
Nearctaphis bakeri (Cowen)
Hypera punctata (Fabricius)
Hypera postica (Gyll.)
Hypera metes (F.)
Hytastinus obscurus (Mar sham)
Apion spp .
Gorz et al . , 1978
Gorz et al. , 1978
El-Kandelgy, 1964
Gorz et al. , 1975
Keller et al. , 1970
Smith et al. , 1975
Gyrisco, 1960
Perju, 1971
128
whereas 'Wegener' was susceptible (Wilcoxson and Peterson, 1960). The opposite
reaction was reported for resistance to the clover aphid ( Nearotaphis bakeri )
in which Dollard and Lakeland were susceptible and Wegener was resistant (El-
Kandelgy and Wilcoxson, 1964). The fecundity of three biotypes of the pea
aphid on 10 cultivars of red clover was studied by Markkula and Roukka (1970).
All the cultivars were moderately resistant to one biotype, susceptible to the
second, and varied from plant to plant within the third biotype. No differ-
ences in the resistance of diploid and tetraploid cultivars were found.
The only example of bred insect resistance occurs with the yellow clover
aphid ( Therioaphis tvifolii) and the pea aphid ( Acyrthosiphum pisum ) (Gorz et
al. 1978, by permission). They selected, in five recurrent cycles, for yellow
clover aphid resistance and in three cycles for pea aphid resistance under
greenhouse conditions. A synthetic, 'N-l' was developed which had resistance
to both aphids. In the 5th cycle, 95.6 percent of the plants were resistant
to the yellow clover aphid, and in the 3rd cycle, 93.7 percent of the plants
were resistant to the pea aphid. Inheritance of resistance was not studied.
RESISTANCE TO NEMATODES
Other than fragmentary reports of resistance to the root-knot nematode
(Ivanoff, 1964; Bain, 1962), most breeding for nematode resistance has been
conducted in Northern Europe with the clover stem eelworm (Ditylenchus dipsaci).
The nematode causes swelling in the cotyledons, in tissues near the growing
point, and in the upper part of the hypocotyl in susceptible plants. Resis-
tant plants are not swollen but exhibit stunted growth. The stands of suscep-
tible cultivars may be eliminated in the seedling year. Personnel of most
European countries have tested resistant varieties developed either by natural
or artificial selection or a combination of both. In Sweden and Finland, the
cultivar 'Merkur' possesses resistance (Bingefors, 1956; Roivainen and Tinnila,
1963). In the Netherlands, only the cultivar 'Flandria' had about the same
resistance as Merkur (Dijkstra, 1956) but in Britain several cultivars had
about the same or greater resistance than Merkur (Fiddian and Aldrich, 1964).
Both tetraploid and diploid progenies were resistant in a test by Toynbee-
Clarke and Bond (1970). They also found good correlation between progenies
infected as seedlings and progenies infected as one-year old plants. No evi-
dence of races were found by Fiddian and Aldrich (1964) but Frandsen (1965)
interpreted his data to show the existence of races, and suggested that clover
breeders should include nematodes from a wide area of clover cultivation. In-
heritance of resistance to stem nematode was studied by Bingefors (1956) by
crossing Merkur (resistant) with 'Altuna' (susceptible). Resistance in the F^
tended to be intermediate between the parent cultivars and no clear genetic
pattern was demonstrated. Nordenskiold (1971) reported that resistance to
the nematode was regulated by two dominant genes. One of the two genes was
closely linked to the S-locus (self-incompatibility).
The Root-Rot Complex
Root-rots of red clover are associated with fungi including Fusavium _,
Trichoderma } Rhizootonia 3 Phoma3 Gliocladium , Leptodisous (Elliott, et al.
1969). Non-fungal organisms that attack roots include the clover root borer
(Hylostinus obscurus) , Sitona sp, and nematodes of various species and genera
(Newton and Graham, 1960) . The pea aphid ( Acyrthosiphum pisum ) and the potato
leafhopper ( Empoasoa fabae ) feed on above ground parts and with viruses in-
129
duces stresses which increase root rot. The total group of root-feeding
organisms acting together has become known as the root-rot complex, which
greatly shortens the life of red clover stands. At any one location, organisms
such as the root-borer and Fusarium may be important and lack of resistance is
usually considered to be a limiting factor. At other locations where the root
borer is not present, Sitona and Leptodiscus spp. are the important agents and
lack of resistance to these organisms is considered to be associated with
short life of red clover. In addition to stresses imposed by several organ-
isms, flowering and seed production in the seedling year have been shown to be
associated with winter injury, and with shortening the life of the stand
(Therrien and Smith, 1960; Smith, 1963). On the other hand, Taylor et al.
(1962) showed that seed production in the year of establishment of clones was
not more detrimental to the stand than forage production provided that plants
had the opportunity to develop rosettes before winter. Stand losses and high
root-rot incidence in Kentucky occur during the summer months rather than in
the winter (Kendall et al. 1962).
It is not surprising that breeding for root-rot resistance has been un-
successful in view of the complexity of agents involved. In an effort to gain
a clear understanding of the situation as it occurs in red clover, Fig. 1 is
presented. With a well adapted cultivar (A y and low incidence of physiological
hazards i.e. proper management, etc. it is expected that clover, being a peren-
nial will persist for several years as has been shown by Crowder and Echeverri
(1961), Crowder and Chaverra (1963) and Gasser and Gagnon (1976). As physio-
logical hazards increase, the persistence decreases. Root-rot organisms will
decrease persistence even further. Such, a situation occurs where clover is
grown in the same fields for many years. With less well adapted cultivar
(B), i.e., one that is introduced from another region or country, the decline
in persistence is much more drastic particularly so with combination of hazards
and root rots. Not illustrated in the figure is the increase in root rots as
physiological hazards are increased as shown by Leath and Byers (1973) in
which diseased roots were more attractive to root borers than healthy roots.
Breeding for resistance to the root rot complex then may be expected to
be effective only by developing broad resistance to wide variety of organisms.
Research at the USDA Pasture Laboratory, State College, Penn., on resistance
to Fusarium is underway. If this type of resistance conveys resistance to
other root rot organisms as well as Fusarium , significant benefit may result.
Hybridization of red clover with strongly perennial species which could change
the character of the root system thus incorporating general resistance has not
been possible to date. The only type of resistance to root rots that exists
today is that possessed by a vigorous well-adapted cultivar growing under a
minimum of physiological hazards, i.e., ideal management conditions. This is
usually termed "field resistance" and is conditioned by a large number of
genes low in heritability or by pleiotropic effects.
METHODS OF INOCULATION
Diseases
Details of inoculation methods necessary for development of resistant
cultivars are given in Table 2. Satisfactory seedling inoculation methods
are available for northern and southern anthracnose, mildew, rust and target-
spot. Optimum temperatures range from 20 to 25 C and for all pathogens except
that of targetspot, the existence of races has been confirmed indicating that
130
YEARS OF STAND MAINTENANCE
HAZARDS TO STAND MAINTENANCE PHYSIOLOGICAL
a ROOT -ROT ORGANISMS
■
FIG, I
RELATION OF PHYSIOLOGICAL HAZARDS AND ROOT-ROT
ORGANISMS IN RED CLOVER.
5.50
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.05
Cv. A. (Well adopted)
Table 2. Details of inoculation methods for breeding for disease
resistance in red clover
Seedling
technique
Optimum
temperature
Season
Races
identified
(°C)
S. anth.
Yes
22-25
Late spring
1
N. anth.
Yes
24
Early spring
18
P. mildew
Yes
24
Fall*
12
Rust
Yes
20
Fall
5
S. leafspot
Yes
20-24
Summer
0
Fusarium
No
28
Summer*
Many species
Crown rot
No
Early spring
0
*Variable.
131
a wide collection of races from different clover growing areas should be used
in inoculation. Unfortunately, the reaction of resistant cultivars in areas
other than where they were developed is not well known. For example, mildew
resistant Tensas may or may not be resistant in Wisconsin where Arlington is
resistant. Because red clover cultivars are heterogenous populations, the
reaction of races must be conducted on individual plants as shown by Hanson
(1966). The lack of effective seedling techniques for Fusarium and So Zero tinia
causes breeding for resistance to these pathogens to be extremely difficult.
Aqueous spore and mycelial suspensions are adequate for the anthracnoses
and targetspot but for rust, a 20:1 (w/w) mixture of talc and urediospores is
used (Engelke, et al. 1975). The mildew pathogen is also applied dry, usually
by placing mildew- inf ectea plants among the population to be selected for
resistance. An epiphytolic is developed by rubbing the diseased plants over
the test plants several times daily (Hanson, 1966).
For virus epiphytotics , plants may be either exposed to pea aphids taken
from infected red clover or peas, or may be inoculated mechanically. In the
latter situation, expressed juice from infected plants is merely rubbed on
plants to be infected which have been dusted with carborundum. Infection
with aphids presents the difficulty of transmitting more than one virus unless
extreme care is taken. Also aphid feeding often causes a virus-like symptom
when no virus is present complicating the selection procedure (Stuteville and
Hanson, 1965). All resistant plants should be examined under field conditions
to reestablish the correlation of seedling and mature plant resistance.
Insects and Nematodes
Inoculation procedures for aphids are greatly simplified as contrasted to
other insects because of adequate greenhouse techniques. Entries to be screened
for resistance are sown in flats of soil with about 35 to 50 seeds in each of
12 rows per flat. Aphid cultures usually are collected from red clover fields
and cultured in growth chambers to eliminate parasites and undesired aphid
species. Seedlings at the unifoliolate leaf stage are infested by shaking
aphids over the plants in each flat. Aphid infestation may be continued up
to two months after which plants are rated on a scale of 1 = highly resistant
to 4 = highly susceptible - dead. Only plants in class 1 are retained for
propagation. If rescreening is necessary, the surviving plants are cut back,
fumigated and reinfested (Gorz et al. 1978, by permission).
In screening for resistance to the stem nematode, infested plants are
collected during the summer, cut off ground level and slowly dried at room
temperature. Eelworms are extracted by placing infected material in metal
sieves which are standing in 8 inch (203 mm) glass funnels lined with milk
filters to remove soil particles. A fine mist of water is then provided
through four 1-mm aperture nozzles. Water pressure is maintained at 20-25
lb /in (1.4 to 1.8 kg/cm^). Eelworms begin to emerge in a few hours and are
carried to the beakers below by the flow of water. Eelworm suspension is
stored in tapwater at 3 C in a refrigerator before inoculation. Seedlings
are inoculated two to three days after germination. One drop of suspension
(approximately 30 eelworms per drop) is placed on each of about 30 seedlings
per entry. Inoculated seedlings are then rolled up in chromatography paper
(No. 1) and inserted in a bottle without water. High humidity is maintained
and after three weeks the seedlings are scored for infection on a scale of
0 = no swelling to 5 = greatly swollen hypocotyl. Seedlings for further
breeding are from classes 0 and 1 (Toynbee-Clarke and Bond, 1970).
132
MECHANISMS OF RESISTANCE
Very little published information is available on the mechanisms under-
lying resistance to red clover pests. Recently, the phytoalexins produced by
red clover leaves challenged by various fungi have been cited for a role in
inhibiting growth of the fungus. Duczek and Higgins (1976) found that the
phytoalexins, medicarpin and maackianin were the only compounds that could
account for the inhibition on red clover of Helminthosporium aarbonum , a corn
pathogen. Biosynthetic pathway studies of these compounds appear to show an
isoflavone origin, particularly formononetin which in itself has little in-
hibitory activity (Debnam and Smith, 1976). The evidence is not clear, how-
ever, inasmuch as differences in accumulation, inhibition, and breakdown of
the phytoalexins were not enough to explain the difference in pathogenicity of
Stemphylium botryosum and S. sarainae forme on red clover (Duczek and Higgins,
1976).
Peroxidase activity in hypersensite , BYMV resistant red clover was found
to be higher than in susceptible clones indicating a possible mechanism of re-
sistance (Sheen et al., 1975).
No studies were found in the literature concerning the causal mechanisms
of resistance to insects or nematodes of red clover.
Problems in Breeding for Pest Resistance
It is obvious from this survey of research accomplishments that the method
used most in breeding for pest resistance is phenotypic recurrent selection.
This is not too surprising because the disease resistance obtained is simply
inherited, and more importantly, easily recognized, with adequate screening
techniques. This is also true in breeding for aphid resistance. Once selec-
tions have been made, it remains only to recombine the selected materials by
crossing under cages, and one generation is easily cycled per year. Escapes
will be eliminated in succeeding generations of selection even though they may
be crossed. In most cases, "vertical” resistance appears to be conditioned by
dominant genes, and the heterozygote is carried along as resistant. Conse-
quently, the selected strain will never become 100% resistant simply by recur-
rent selection. This is not of overriding importance, however, and may even
be insurance against mutation of new pathogenic races as have occured in self
pollinated cultivars. The presence of many cultivars of red clover in dif-
ferent regions of the world also mitigates against this possibility.
While pest resistance selection is simple, it is sometimes more difficult
to maintain the desirable characters of a cultivar while increasing pest re-
sistance. If the number of resistant plants in any one cycle is too low, in-
breeding depression and loss of vigor may result. The selection of 100 plants
results in a theoretical inbreeding coefficient of 0.5% and perhaps represents
a practical lower limit of selected plants. Of equal or greater importance is
the selection of resistant plants on an annual basis. Some research seems to
indicate that such selection may produce more annual genotypes and loss of the
persistence characteristic of the modern red clover cultivars. In a backcross
program to incorporate mildew resistance at the Kentucky Station, the mildew
resistant line was similar to the recurrent parent, * Kenstar', in all charac-
ters except earliness of bloom. Apparently some unintential selection had
occurred during the backcross procedure. Earliness in clover has been shown
to be associated with lack of persistence (Taylor et al. , 1966). More research
is needed concerning means of overcoming such selection on an annual basis.
133
One suggestion is to select only those plants responding to longer photoperiods.
These later types should retain persistence.
The problem of races has been referred to earlier, but should be empha-
aized again. A broad spectrum of races should be used during the screening
process. This may complicate inheritance patterns somewhat but recurrent
selection procedures probably will be adequate.
A somewhat more difficult problem is that of non-specific or general re-
sistance which the more adapted cultivars seem to possess. One cannot expect
to easily transfer this type of resistance because it is dependent upon many
genes, or may be even due to pleiotropic effects. The field resistance to the
rcot-rots, crown rot and perhaps some insects and nematodes may be of this
type. If cultivars with this type resistance are transferred to areas where
they are unadapted, they may no longer be resistant. Caution should be exer-
cised in attributing specific resistance to a particular disease to a well
adapted cultivar. It may be resistant because it is adapted, rather than
adapted because it is resistant.
SUMMARY
Progress in the development of pest resistance in red clover has been
made over the last 20 years particularly with diseases. However, resistances
have been combined only in a few cultivars. Much less research has been con-
ducted on insect or nematode resistance. Resistance to specific diseases have
been found to be controlled by one or a few dominant genes, but insect resis-
tance inheritance studies are lacking. Most breeding has utilized phenotypic
recurrent selection, and in a few cultivars, the backcross method. These
methods are used because resistance is simply inherited, seedling inoculation
techniques are available, and resistance is easily recognized. A more dif-
ficult problem is the maintenance of cultivars without change in other desired
characters. Little attention has been directed toward understanding mecha-
nisms of resistance to specific red clover pests. Although the root rots have
received considerable attention, little progress has been made primarily due
to the complex and varied nature of pathogens and parasites on clover roots.
Well adapted, vigorous, persistent cultivars possess a broad or field type of
resistance which enables them to yield and persist well in spite of root rots
and physiological hazards.
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137
ENZYME-LINKED IMMUNOSORBENT ASSAY (ELISA) FOR DETECTION AND
IDENTIFICATION OF FORAGE LEGUME VIRUSES
By M. R. McLaughlin and O. W. Barnett
Detection and identification of plant viruses is an essential part of any plant breeding
program on virus resistance. This is usually done by combining greenhouse tests involving
the inoculation of a series of indicator host plants with serology, electron microscopy, and
other laboratory procedures (1). The investment in facilities, equipment, expertise, and
time required for successful application of these methods can be a considerable obstacle to
plant breeders and plant pathologists working in this important area.
The need for a simple, rapid, sensitive, reliable, and practical means of virus detec-
tion and identification prompted us to examine a relatively new serological procedure, the
enzyme-linked immunosorbent assay (ELISA) (2). This procedure offers the advantages of
specificity, speed, and ease of standardization provided by conventional serological meth-
ods, while overcoming problems due to low virus concentrations and particle morphology
which often limit the effectiveness of conventional methods (3). The development of ELISA
and its application to detection and identification of some forage legume viruses is described
in this paper.
DEVELOPMENT OF ELISA
Labelled antibodies have been used for a number of years to increase the sensitivity of
serological procedures in detection of viral antigens. Traditionally, fluorescent dyes and
radioisotopes have been used as labels. More recently the use of enzyme-labelled anti-
bodies (4) was shown to be useful in light microscopic detection of viral antigens in tissues.
The pioneering work of Engvall and coworkers (5, 6, 7) and Van Weeman and Schuurs (8, 9)
demonstrated that enzyme-labelling procedures could also be quantitative and exhibit sensi-
tivities comparable to radioimmunoassay techniques. Engvall and Perlmann first introduced
the acronym, ELISA, in 1971 (5). In 1974 Voller et al. (10) adapted ELISA to a micro-
plate method. In 1976, in a review of the theory and practice of enzyme immunoassays in
diagnostic medicine, Voller, Bidwell, and Bartlett (11) described the "double antibody
sandwich" form of ELISA.
In this method (Fig. 1) specific antibodies are adsorbed to a solid surface in wells of
polystyrene microtiter plates (Dynatech Laboratories, Inc.). A test sample suspected to
contain the viral antigen is incubated in the wells and any virus recognized by the antibody
is bound. Subsequent reaction of the bound virus with enzyme-labelled specific antibody
results in formation of the "double antibody sandwich." This complex is then detected by
addition of an appropriate substrate with which the enzyme reacts to form a colored product.
Qualitative visual ratings or quantitative spectrophotometric measurements can be made of
138
1 . Specific antibody adsorbed
to polystyrene
RINSE
2. Addition of test sample
Specific antigen (virus) bound
by adsorbed antibody.
RINSE
3. Addition of enzyme-label led
specific antibody
Formation of "double antibody sandwich"
RINSE
4. Addition of enzyme substrate
Formation of colored reaction product
5. Qualitative visual rating or
quantitative spectrophotometric
measurement of reaction product
FIGURE 1. — The double antibody sandwich ELISA for plant viruses (11).
139
the colored product. In the absence of the specific viral antigen in the test sample, the
double antibody complex cannot be formed; therefore, no enzyme is present, and no color
change occurs upon addition of the substrate.
It was in this form that ELISA was first applied to the detection of plant viruses (2).
In 1977 Clark and Adams (3) described the method in detail as it applies to the detection of
plant viruses. This form of ELISA has found rapid and widespread acceptance among plant
virologists and has been applied to a variety of viruses including: arabis mosaic virus, plum
pox virus, strawberry latent ringspot virus, raspberry ringspot virus, hop mosaic virus,
prunus necrotic ringspot virus, apple stem grooving virus, and apple chlorotic leafspot virus
(2, 3, 12); tomato ringspot virus (13); peach rosette mosaic virus (14); soybean mosaic virus
and tobacco ringspot virus (15); apple mosaic virus (16); potato leafroll virus (17); potato
virus S and potato virus X (18); prune dwarf virus (19); pea seed-borne mosaic virus (20);
cucumber mosaic virus (21); and many others, the reports of which are yet to be published.
PREPARATION OF ENZYME-LABELLED ANTIBODY
Protein fractions containing specific antibodies were prepared by sodium sulfate pre-
cipitation (8). From 1 to 5 ml of antiserum was brought to 5 ml with distilled water, then
antibody protein was precipitated by addition of an equal volume of 36% sodium sulfate in
aqueous solution. Antibody protein precipitates were collected by centrifugation for 15 min
at 6,000 xg, washed once with 18% sodium sulfate in aqueous solution, resuspended in phos-
phate-buffered saline (PBS - 0.02 M phosphate, 0.15 M NaCI, 0.003 M KCI, pH 7.3) and
dialyzed exhaustively against PBS at 4 C. Antibody protein concentrations were estimated
spectrophotometrically (Ei^;m= 1 .5). Volumes of 0.5 to 1 .0 ml of antibody protein at 2.0
mg per ml in PBS were reserved for enzyme labelling, while a second portion of the antibody
protein solution at 1 .0 mg/ml was adjusted to 0.02% NaNg and stored at 4 C for later use
in coating plates. The antibody protein reserved for enzyme labelling was mixed with an
equal volume of alkaline phosphatase [EC No. 3. 1.3.1, Sigma Type VII, 5 mg/ml in a
crystalline suspension of 3.2 M (NH4)2S04 solution, pH 7, containing 0.001 M MgCl2 and
0.0001 M ZnCl2]. The mixture was dialyzed against several changes of PBS at 4 C, then
25% glutaraldehyde in aqueous solution was added to a final concentration of 0.2%, and
the mixture was incubated at room temperature 2 hr, then dialyzed exhaustively against PBS
at 4 C. The enzyme-antibody conjugate was then dialyzed against 0.05 M Tris-HCI, pH 8
containing 0.15 M NaCI (Tris-buffered saline = TBS). The conjugates were adjusted to 0.5
mg antibody per ml in TBS, made up to final concentrations of 1 .0% BSA (bovine serum
albumin) and 0.02% NaNg and stored in the dark at 4 C.
THE ELISA METHOD
The "double antibody sandwich" form of ELISA (11) was used according to the proce-
dures of Clark and Adams (3) with some modifications. Protein-binding polystyrene micro-
elisa plates (cat. no. 1-223-29, Dynatech Laboratories, Inc., 900 Slaters Lane, Alexandria
VA 22314) with flat-bottomed wells were coated with specific antibody by adjusting anti-
body protein preparations (1 .0 mg/ml in PBS) to from 1 .25 to 5.0 pg per ml (the optimal
concentrations varied between preparations) in carbonate coating buffer (0.05 M sodium car-
bonate, pH 9.6, containing 0.02% NaNg) and incubating the antibody in the plates (200 pi
140
10
5 2.5 1.25
Coating antibody protein (pg/m!)
5 2.5 1.25 10 5 2.5 1.25 10
IQ"1
10~2
>
”5
c
CO
CO
o
-h
CD
O
-t-
CD
, -4
Q_
10
~o
Q
-5
3
-f
10
to
a
*o
-6
10 °
~o
«
o
9 CD
3-
io“2
d =r
XI ''
FIGURE 2. --Placement of reactants to determine optimal concentrations for coating
and enzyme-labelled antibody.
per well) for 4 hr at 30 C. Nonadsorbed antibody protein was rinsed from the wells by
three 3-min washes in PBS containing 0.05% Tween 20 (PBS-Tween). Test samples contain-
ing purified virus in PBS-Tween or plant extracts in PBS-Tween containing 2% polyvinyl
pyrrol i done (PVP 40,000 MW) were incubated in the plates (200 pi per well) overnight at
4 C. Test samples were rinsed from the wells with distilled water followed by three washes
in PBS-Tween. Enzyme-labelled antibody at concentrations of 0.625 to 2.5 pg per ml (the
optimal concentrations varied between preparations) was added to the plates (200 pi per
well) and incubated 4 hr at 30 C. Unbound enzyme-labelled antibody was rinsed from the
wells with PBS-Tween as before and 200 pi of enzyme substrate (p-nitrophenyl phosphate,
5-mg tablets. Sigma Chemical Co.) at 1 .0 mg per ml in 10.0% diethanolamine was added
to each well . Substrate solutions were incubated in the plates at room temperature for 1 to
3 hr, then 50 pi of 3 M NaOH was added to each well to stop the enzyme-substrate reac-
tion. Dephosphorylation of p-nitrophenyl phosphate yielded a yellow-colored product, p-
nitrophenol . The presence and intensity of the yellow color was scored visually and/or
measured spectrophotometrical ly . Spectrophotometric measurements were made by diluting
the contents of each test well in 1 .0 ml distilled water and reading its absorption through a
1 -cm light path at 400 nm in a GCA/McPherson Model EU700 spectrophotometer.
Optimum concentrations of coating and enzyme-labelled antibody preparations were
determined experimentally according to the design in Fig. 2.
141
TABLE 1 .—Comparison of ELISA detectable dilution end points (DDEP) with
Snfectivity dilution end points (DEP) from alfalfa mosaic, bean yellow
mosaic, clover yellow mosaic, clover yellow vein, and white
clover mosaic virus-infected plant tissue
Virus (Source plant)
ELISA DDEP
Infectivity DEP (Indicator host)
AMV (white clover)
10-5
-2
10 (Bountiful bean)
BYMV (white clover)
]Q“3
-3
10 w (C. amaranticolor)
BYMV (Alaska pea)
IQ"3
CYMV (white clover)
at least 10 ^
10 ^ (C. quinoa)
CYW (white clover)
io"2
“2
10 (C. amaranticolor)
CYW (Alaska pea)
io”3
WCMV (Alaska pea)
io"4
at least 10 2 (Bountiful bean)
WCMV (Bountiful bean)
1Q"3
10 ^ (Bountiful bean)
WCMV (white clover)
10"6
* Not tested.
PROGRESS
To date we have prepared and tested enzyme-conjugated antibody to alfalfa mosaic
virus (AMV), bean yellow mosaic virus (BYMV), clover yellow mosaic virus (CYMV), clover
yellow vein virus (CYW), two isolates of peanut stunt virus (PSV), red clover vein mosaic
virus (RCVMV), and white clover mosaic virus (WCMV). With the exceptions of theRCVMV
system, which has not been fully examined, and the PSV systems, which showed positive re-
actions against some healthy plant sap preparations, the ELISA results with these virus sys-
tems have been very encouraging.
Comparisons of ELISA detectable dilution end points (DDEP) with infectivity dilution
end points (DEP) (Table 1) showed ELISA methods to be at least as sensitive and sometimes
more sensitive than conventional infectivity tests, with one exception. In the case of
WCMV, a virus which is relatively very stable, reaches relatively high concentrations in
infected plants, is very easily mechanically transmitted, and probably carries all of its
genetic information in a single particle, infectivity tests proved more sensitive than ELISA.
A contrasting situation was observed with AMV, which has a split genome and requires mul-
tiple nucleoprotein particles each with a different complement of genetic material to be
present at the site of inoculation in order to produce infection (22). All the nucleoprotein
components of AMV share common antigenic properties (22), and so it was not surprising
that AMV was detected serologically at dilutions where its components were too widely dis-
persed to cause infection.
In tests using 200-pl samples of purified virus, ELISA detected WCMV in amounts as
low as 2 to 20 ng and CYW as low as 20 ng. Concurrent tests with latex-conjugated anti-
bodies (23) have shown ELISA to be at least as sensitive as latex serology and sometimes 10
142
to TOO fold more sensitive depending upon which preparations of the respective conjugates
were compared.
In tests of field-collected material, 27 clover samples, which had previously been
indexed for viruses by inoculation to indicator host plants, were tested with ELISA for
BYMV, CYVV, and WC MV. Following host indexing, the samples had been held at 18 C
for 4 days and were in generally poor condition when used for ELISA, yet in all but four
cases the results of the two indexing methods were in full agreement. In two instances
ELISA failed to detect WCMV which the indicator hosts did detect. In both cases the con-
centration of WCMV in the tissue samples was very low, as indicated by very few chlorotic
local lesions on the primary leaves of cowpea test plants. In one case the particular sample
had been included in the test because it was almost totally rotted and we wanted to see if it
was still usable. In the remaining two cases of nonagreement, ELISA detected BYMV which
the indicator hosts did not. In this comparative test, ELISA was often useful in determining
whether a particular sample contained BYMV, CYVV, or both. Such distinction could not
be made based upon the reaction of the indicator host, Chenopodium amaranticolor Coste
and Reyn0, because both viruses produced similar necrotic local lesions.
Results of a similar comparative test of 70 field samples representing various clover
species showed total agreement between ELISA and greenhouse tests with indicator host
plants. Unfortunately for the comparison, both systems indicated no virus infection in any
of the samples, making it difficult to evaluate the performance of either method.
USE OF ELISA IN COOPERATIVE PROJECTS
One of the most encouraging findings concerning ELISA was that microtiter plates
could be sensitized with specific antibody and sent via regular mail service to cooperating
scientists. The cooperators need only to add the appropriate test and control plant sap
samples to the plates, store them overnight in the refrigerator, rinse out the samples with
distilled water, and send the plates back by return mail. The ELISA tests may then be com-
pleted at the laboratory of their origin. This use of ELISA offers a new dimension in re-
search potential to the plant breeder or plant pathologist who might otherwise not be
equipped to do virus detection and identification work, and the opportunity for regional
research cooperation is greatly enhanced. A single research center capable of preparing
and completing ELISA tests could supply plates to several cooperators, thereby extending
virus detection and identification programs throughout the region.
Such cooperative efforts have begun already. Microtiter plates sensitized at Clemson
have been sent to cooperators in the S-127 Regional Project on Forage Legume Viruses. The
response of cooperators has been positive and early results have been favorable.
SUMMARY
Enzyme-linked immunosorbent assay (ELISA) is a research tool which offers several
advantages.
1 . Virus screening tests, which formerly required inoculation of several indicatorhost
plants, took up to three weeks to complete, and required a considerable investment
in greenhouse space, may be completed in a matter of hours with ELISA.
-2. Comparative tests have shown ELISA to be generally as reliable and often more
sensitive than conventional indicator host assays.
143
3. Sensitized ELISA plates can be mailed to research cooperators who may add test
samples and return the plates for completion of testing, thereby opening up new
cooperative research potential.
ACKNOWLEDGMENTS
This is a report of research in support of regional project S-127 and funded coopera-
tively by the South Carolina Agricultural Experiment Station and the Science and Education
Administration, United States Department of Agriculture.
REFERENCES
1. Barnett, O. W., and P. B. Gibson. 1977. Identifying virus resistance in white
clover by applying strong selection pressure. I. Technology. Proc. 34th Annual
Southern Pasture and Forage Crop Improvement Conference. Auburn University,
Auburn, Alabama. April 12-14, 1977. p. 67-73.
2. Voller, A., A. Bartlett, D. E. Bidweli, M. F. Clark and A. N. Adams. 1976. The
detection of viruses by enzyme-linked immunosorbent assay (ELISA). J. Gen.
Virol. 33: 165-167.
3. Clark, M. F., and A. N. Adams. 1977. Characteristics of the microplate method of
enzyme-linked immunosorbent assay for the detection of plant viruses. J. Gen.
Virol. 34:475-483.
4. Wicker, R., and S. Avrameas. 1969. Localization of virus antigens by enzyme-
labelled antibodies. J. Gen. Virol. 4: 465-471 .
5. Engvall, E., and P. Perlmann. 1971. Enzyme-linked immunosorbent assay (ELISA).
Quantitative assay of immunoglobulin G. Immunochemistry 8 : 871-874.
6. Engvall, E., K. Jonsson, and P. Perlmann. 1971. Enzyme-linked immunosorbent
assay. 11. Quantitative assay of protein antigen, immunoglobulin G, by means of
enzyme-labelled antigen and antibody coated tubes. Blochim. Biophys. Acta
251: 427-434.
7. Engvall, E., and P. Perlmann. 1972. Enzyme-linked immunosorbent assay, ELISA.
III. Quantitation of specific antibodies by enzyme-labeled anti-immunoglobulin
in antigen-coated tubes. J. Immunology 109: 129-135.
8. Van Weemen, B. K., and A. H. W. M. Schuurs. 1971. Immunoassay using antigen-
enzyme conjugates. FEES Letters 15: 232-236.
9. Van Weemen, B. K., and A. H. W. M. Schuurs. 1971. Immunoassay using antigen-
enzyme conjugates. FEBS Letters 24: 77-81 .
10. Voller, A., D. Bidweli, G. Huldt, and E. Engvall. 1974. A microplate method of
enzyme-linked immunosorbent assay and its application to malaria. Bull. World
Health Organ. 51 : 209-21 1 .
11. Voller, A., D. E. Bidweli, and A. Bartlett. 1976. Enzyme immunoassays in diag-
nostic medicine. Theory and practice. Bull. World Health Organ. 53: 55-65.
12. Thresh, J. M., A. N. Adams, D. J. Barbara, and M. F. Clark. 1977. The detec-
tion of three viruses of hop (Humulus lupulus) by enzyme-linked immunosorbent
assay (ELISA). Ann. Appl. Biol. 87:57-65.
144
13. Converse, R. H. 1978. Detection of tomato ringspot virus in red raspberry by enzyme-
linked immunosorbent assay (ELISA). Plant Dis. Rep. 62: 189-192.
14. Ramsdell, D. C. 1977. Detection of peach rosette mosaic virus (PRMV) in 'Concord'
grape: comparison of ELISA vs. Chenopodium quinoa indexing. Proc. Amer.
Phytopathol. Soc. 4: 91 (Abstr.).
15. Lister, R. M. 1977. Detection of viruses in soybean seed by enzyme-linked immuno-
sorbant assay. Proc. Amer. Phytopathol. Soc. 4: 132 (Abstr.).
16. Hardcastle, T., and A. R. Gotlieb. 1977. Detection of the yellow birch strain of
apple mosaic virus (APMV) using enzyme-linked immunosorbent assay (ELISA).
Proc. Amer. Phytopathol. Soc. 4: 188 (Abstr.).
17. Casper, R. 1977. Detection of potato leafroll virus in potato and in Physaiis floridana
by enzyme-linked immunosorbent assay (ELISA). Phytopath. Z. 90: 364-368.
18. Richter, _!., W. Augustin, and H. Kleinhempel. 1977. Nachweis des Kartoffel-S-
virus mit hilfe des ELISA-testes. Arch. Phytopathol. und Pflanzensch., Berlin
13: 289-292.
19. Casper, R. 1977. Assay of Prunus avium seed for prune dwarf virus by ELISA.
Phytopathol. Z. 90: 91-94.
20. Hamilton, R. I., and C. Nichols. 1978. Serological methods for detection of pea
seed-bome mosaic virus in leaves and seeds of Pisum sativum. Phytopathology
68: 539-543.
21. Gera, A., G. Lobenstein, and B. Raccah. 1978. Detection of cucumber mosaic
virus in viruliferous aphids by enzyme-linked immunosorbent assay. Virology
86: 542-545.
22. Bos, L., and E. M. J. Jaspars. 1971. Alfalfa mosaic virus. C.M. I ./A.A.B.
Descriptions of plant viruses. No. 46. Commonwealth Mycological Institute,
England.
23. Abu Salih, H. S., A. F. Murant, and M. J. Daft. 1968. The use of antibody-
sensitized latex particles to detect plant viruses. J. Gen. Virol. 3: 299-302.
145
COLLECTION OF CLOVER SPECIES IN GREECE, CRETE, AND ITALY
By R. R. Smith, N. L. Taylor, and W. R. Langford
The first phase of a three-phase Tri folium (clover) seed exploration was
conducted during June and July, 1977 in Greece and Italy. The initial proposal
was drafted by Dr. N. L. Taylor, University of Kentucky on behalf of clover
workers in eastern United States. This proposal was submitted to USDA, Science
and Education Administration (SEA) Plant Germplasm Coordinating Committee in
December of 1975. This proposal was subsequently subdivided into three phases.
The first phase was to collect seed and associated Rhizobia biotypes of Tri-
folium ambiguum M. Bief., T. montanum L. , T. noricum Wulf., T. patulum Tausch. ,
T. pignantii Brogn. and Bory. , T. pratense L. , T. repens L. , T. uniflorum L. ,
and T. wettsteinii Dorfl. and Hay. in Greece, Italy and Yugoslavia.
The first phase was approved and funded through the USDA, SEA Plant Germ-
plasm Coordinating Committee. Specific details for conducting this exploration
and collection were initiated in December, 1976 through the offices of Mr.
Wilfred Phillipsen, Mr. Elmer Hallowell, and Mr. Robert Svec, Agricultural
Attaches in Greece, Italy, and Yugoslavia, respectively, and scientists in
each country. Contacts and preliminary arrangements were made with the assis-
tance of Dr. George Boudonas, Director, Agricultural Research Service of Greece
and Mr. E. Porceddu, National Germplasm Institute of Italy. Attempts were made
from the U.S. and through the Agricultural Attache’s office to contact appro-
priate Yugoslavian officials or scientists for assistance. Contact was finally
made with the Yugoslavian Ministry of Agriculture through Mr. Svec's office on
June 21, 1977 after starting the trip in Athens, Greece. The initial program
proposed exploring and collecting in Yugoslavia for seven days, however, it
was impossible to firm up details with the Yugoslavian government in time to
conduct an exploration there. The seven days programed initially for Yugo-
slavia were then spent on additional collection sites in Greece.
The exploration trip began on June 20, 1977 in Athens, Greece by the
senior author and Dr. W. R. Langford, Director Southern Regional Plant Intro-
duction Station, Experiment, GA. Accessions were collected in Greece from
June 21 to July 5, in Crete July 6-8, and in Italy July 12-21. Table 1 has
the complete list of accessions of Tri folium species collected in Greece,
Crete, and Italy during June and July, 1977. All collections were made in
native pastures, mountain meadows, natural forests, and undisturbed country
roadsides.
COLLECTION IN GREECE AND CRETE
Detailed arrangements for assistance at each location in Greece were ar-
ranged through Mr. Phillipsen and Dr. Boudonas’ s offices. The route traveled
and areas explored in Greece are shown in Figure 1. The central points of
operation were Thessaloniki (Macedonia Province) , Larisa and Trikkila (Thessali
Province), Ioannina (Epirus Province), and Chania, Crete.
146
TABLE 1. Number of accessions of Trifolium species collected in
Greece, Crete and Italy during June and July, 1977
Species
q j
Number^- of
Greece
accessions
Crete
from
Italy
Total
alexandrinum
2
1
3
alpestre
2
-
- (1)
2 (1)
angusti folium
6
-
1
7
arvense
2
2
1
5
oampestre
7
2
4
13
oanesoens
5
-
15
20
oherleri
2
1
1
4
eohinatum
5
-
-
5
fragiferum
2 (3)
2
2 (2)
6 (5)
globosum
1
-
-
1
glomeratum
1
4
-
5
he Idreiohianum
1
-
- (1)
1 (1)
hirtum
3
-
3
hybridum
1
-
4
5
inoarnatum
-
-
3
3
ligusticum
-
1
-
1
montanum
-
-
1
1
medium
3
-
7 (1)
10 (1)
nigresoens
4
4
- (1)
8 (1)
pallidum
11
7
-
18
phloeides
2
-
1
3
physodes
-
1
-
1
pr a tense
6 (3)
-
33 (1)
39 (4)
repens
28 (4)
4
15 (2)
47 (6)
resupinatum
3
2
-
5
retusum
2
-
-
2
rubens
1
-
-
1
soabrum
4
1
1
6
stellatum
1
2
1
4
spumosum
1
-
-
1
squamosum (maritimum)
4
2
-
6
squarrossum
-
-
1
1
subterraneum
1
2
-
3
suffocatum
-
1
-
1
tomentosum
-
2
1
3
uniflorum
1
-
-
-
unknown 1
4
-
-
4
unknown 2
5
1
-
6
spp.
- (6)
- (2)
- (10)
- (18)
Total no. species
31
18
18
37- /
a/
— Value in parenthesis is number of
nonviable seed.
that species
with
HJ Total number of species,
viable seed and 37 with nonviable
A total
seed .
of
254 accessions with
147
The areas explored in Macedonia Province were around the village of Sere
and in the Menikion Mts. (max. 1500-1700 m elevation - area 1), around the vil-
lage of Beria and in the Vermion Mts. (max. 1700-1800 m elevation - area 2),
and central (Polygyras) and western extension of the Khalkidhiki penninsula
(max. 400 m elevation - area 3). Species collected in this region are listed
in Table 2. Most collections in this region were obtained at elevations greater
than 400 m in high mountain meadows being grazed by sheep and goats. The ex-
ception to this was along the coast of the central extension of the Khalkidhiki
penninsula.
The areas explored in the Thessali Province were the village of Trikkala
and Lake Megthobas (max. 1500 m elevation - area 4), the villages of Elasson
and Olympia and base of Mt. Olympus (max. 1000 m elevation - area 5), and vil-
lage of Volos and Pilion Mts. (max. 1000 m elevation - area 6). Species col-
lected in this region are listed in Table 3. This region has a wide range of
clover species (19 collected in this area). Generally, the annual species
were observed at lower elevations with less rainfall and perennials most fre-
quently observed in the mountains where rainfall was more plentiful. Thirteen
collections were made around the village of Trikkila in small native community
pastures (elevation less than 100 m) . Probably the most productive area of
Greece was in the Pilion Mountains near Volos between 650 and 900 m. It was
this region where the one collection of T. uniflorum was obtained.
The areas explored in the Epirus Province were the route between Larisa
and Ioannina to include the village area of Metsovan and the Peristeri Mts.
(max. 1800 m elevation - area 7) and the regions around the villages of
Ioannina, Delvinaki (max. 1000 m elevation - area 8), and Konista. Species
collected in this region are listed in Table 4. All five collection of T.
eohinatum were obtained in this region at elevations between 500 and 1500
meters. Collections were made in northern Greece within 1 kilometer of the
Albanian border.
The western tip of the island of Crete was explored around the villages
of Chania, Kastelli, Platanos, and Elos and in the Lefka Ori mountains near
the villages of Dmalos (1100 m) and Limni (400 m) . Eighteen species of Tri-
folium were collected in this region (Table 5). Specimens were very difficult
to identify in this area. Most plants were dry with dislodged seed heads.
All species collected were annuals except T. fragiferum, physodes, and repens.
COLLECTION IN ITALY
Detailed arrangements for collection in Italy were arranged in cooperation
with National Laboratory of Germplasm in Bari through Mr. Hallowell, Agricul-
tural Attache, office. Dr. Pierluigi Spagnoletti of the Germplasm Laboratory
accompanied Smith and Langford on the entire trip providing guidance and trans-
lating while collecting specimens for his laboratory. Collections were made
throughout the Appennino Mountains through central and northwestern Italy
(Figure 2). Collections were also made in the Gargano area (area 1). Eleven
species were collected in this region between the 41st and 43rd north latitude
region (Table 6). Trifolium species angusti folium, arvense 3 oherleri 3
phloeides 3 soabrum 3 stellatum 3 and tomentosum were observed only in this re-
gion of Italy. Unlike the pinkish white-flowered collections of T. stellatum
obtained in Greece this collection was yellow-flowered. Trifolium species
alexandrinum 3 canescens 3 fragiferum 3 hybridum 3 inaarnatum 3 mantanum 3 and
squarossum were not observed until we were north of the 43° latitude (Table
( Continued on page 153.)
148
42°
Figure I. Outline map of Greece showing route
traveled & areas explored for Trifoiium spp.
42°
40°
38°
36°
149
TABLE 2.
a/
Trifolium species— collected near
Thessaloniki in Macedonia Province, Greece
alexandrinum (2)
pratense (2)
angusti folium (2)
repens ( 9 )
arvense (1)
resupinatum (1)
globosum (1)
retusum (2)
glomeratum (1)
seabrum (1)
hirtum (1)
spumosum (1)
nigrescens (1)
pallidum (4)
unknown 1 (2)
— Number of accessions in parenthesis .
TABLE 3.
• • 3 /
Trifolium species— collected near Trikkila in
Thessoli Province, Greece
alpestre (2)
angusti fqlium (3)
arvense (2)
campestre (4)
canescens (5)
cherleri (1)
fragiferum ( 2 )
heldreichianum (1)
hirtum (2)
medium (3)
nigresoens (3)
pallidum (3)
phloeides (2)
repens (13)
resupinatum (1)
seabrum (2)
squamosum (2)
(maritimum)
uniflorum (1)
unknown 1 (2)
a/
Number of accessions in parenthesis.
TABLE 4.
• • 3. f
Trifolium species— collected near Ioannina in
Epirus Province, Greece
angusti folium (1)
campestre (3)
cherleri (1)
echinatum (5)
fragiferum (1)
hybridum (1)
pallidum (2)
pratense (3)
repens (6)
resupinatum (1)
rubens (1)
seabrum (1)
stellatum (1)
squamosum (1)
(maritimum)
subterraneum (1)
unknown 2 (3)
a/
Number of accessions in parenthesis.
150
. . a/
TABLE 5. Trvfolvum species— collected on island of Crete
arvense (2)
aampestre (2)
eherleri (1)
fragiferum (2)
glomeratum (4)
ligustieum (1)
nigreseens (4)
pallidum (7)
physodes (1)
repens (4)
resupinatum (2)
seabrum (1)
stellatum (2)
squamosum (2)
(maritimum)
subterraneum (2)
suffocatum (1)
tomentosum (2)
unknown 1 (1)
— Number of accessions in parenthesis.
3. /
TABLE 6. Trifolium species— collected in central
Italy in Appennino Mts. between 43 and
41 N. latitude
angusti folium (1)
pratense (12)
arvense (1)
repens (8)
aampestre (2)
seabrum (1)
eherleri (1)
stellatum (1)
medium (1)
tomentosum (1)
phloeides (1)
a/
Number
of accessions
in parenthesis.
3 /
TABLE 7. Trifolium species— collected in central
and northeast Italg in Appennino Mts.
between 45 and 43 N. latitude
alexandrinum (1)
montanum (1)
campestre (2)
medium (6)
caneseens (15)
pratense (21)
fragiferum (2)
repens ( 7 )
hybridum (4)
squarrossum (1)
inaarnatum (3)
— Number of accessions in parenthesis.
151
46®
46°
44®
42
40
38
Figure 2. Outline map of Italy showing route
traveled 8 areas explored for
Tnfoiium spp.
152
7). Both T. pvatense and T. repens were observed throughout the region with
T. pratense more frequent at the higher elevations.
DISPOSITION OF COLLECTED SAMPLES
Samples were forwarded through the respective agricultural attaches' of-
fices to The Plant Quarantine Station at Beltsville Agricultural Center.
After appropriate inspection and clearance the samples were forwarded to the
Germplasm Resources Laboratory, SEA, Beltsville, Maryland for assigning plant
introduction numbers (P.I.'s) and further documentation. All Tri-folium sam-
ples were then forwarded to the senior author at the University of Wisconsin,
Madison, WI through W. R. Langford. Samples were threshed and cleaned during
September, 1977. Approximately eighteen germinated seedlings of each viable
species were transplanted to small plastic trays in the greenhouse. Verifi-
cation of identity of each collection was then made with the assistance of
the junior author over the period between December, 1977 to May, 1978. All
flowering cross-pollinated species were enclosed in screened cages with honey-
bees in the greenhouse. Notes such as flowering date, flower color, height,
etc. were recorded on each species as they came into flower. Each species
that flowered was photographed and a herbarium specimen taken. At the pre-
sent time seed is being harvested from all species that flowered. Perennials,
such as T. repens3 pratense3 oanesoens 3 rubens} alpestre3 medium3 montanum3
heldreiahianum 3 and several unknowns which flowered poorly or not at all were
transplanted to the field in May, 1978. Increased seed and remnant original
seed will be forwarded to either the Southern Plant Introduction Station (an-
naul species) or the Northeastern Plant Introduction Station (perennial spe-
cies) .
DISCUSSION
Species collected on only the mainland of Greece, the island of Crete, or
in Italy are listed in Table 8. T. pallidum was not observed in Italy while
the three collections of T. incamatum all came from the central region of
this country. The one yellow-flowered T. stellatun was collected in Italy,
but the three pinkish white-flowered accessions were obtained in Greece.
Usually the T. eaneseens was obtained at high elevations in Italy. T. oam-
pestre and angustifolium could have been collected throughout much of the ex-
plored area. T. oampestre was probably the most widely distributed species.
Hardly any stop was made without observing a few specimens of this species.
T. repens was probably the second most widely distributed species.
The period between June 20 and July 26, was probably not the most appro-
priate period for collecting either the annual or perennial species. In
general, most of the annual species were very dry and difficult to identify
from the plant specimen. Identification in most cases was based on head or
seed type. A month earlier (May 15 - June 15) would be the more appropriate
period to observe and collect the annuals. On the other hand, many of the
perennials were just beginning to flower between June 20 and July 26, making
it very difficult to obtain dry seed of these species. Therefore, we would
recommend attempting future collection trips to be compatible with either the
annuals or perennials. Possibly the perennials might be collected with late
annuals .
In addition, sheep and goats had grazed many of the community native
pastures and high elevation meadows making it difficult to locate species in
153
TABLE 8.
Trifolium species— 7 collected in either Greece,
Crete, or Italy
Greece
Crete
Italy
alpestre (2)
ligustioum (1)
inoarnatum (3)
eohinatum (5)
physodes (1)
montanum (1)
globosum (1)
heldreiehianum (1)
hirtum (3)
retusum (2)
rubens (1)
spumosum (1)
uniflorum (1)
unknown 1 (4)
suffocatum (1)
squarrossum (1)
— Number of accessions in parenthesis.
most of these areas. Considerable plant material is available in the areas
explored and the grazing problem would not have been as serious if the trip
had been earlier.
It was difficult to observe rhizobium nodules on most of the dry annuals
so no attempt was made to collect them on many accessions. The common species,
such as T. pratense and T. repens were only sampled for rhizobium periodically.
Collections of bacteria were made on the following species: T. alexandrinum
(2 samples), T. oampestre3 T. canescens (3 samples), T. fragiferum3 T. hybridum 3
T. medium3 T. negrisoens3 T. pratense (2 samples), T. repens (5 samples), T.
squarrosum (1 sample) and one unknown. Samples were forwarded to Dr. Dean
Weber, Cell Culture Laboratory, SEA, Beltsville, Maryland.
Of the initial species outlined in the objectives only T. pratense and T.
repens were observed and collected with any regularity. T. ambiguum3 patulum 3
pignantii3 and wettsteinii were not collected or even observed in any areas
explored. Only one specimen each of T. montanum and T. uniflorum was observed
and collected. T. montanum was collected at 800 m elevation along Route 523,
five km west of Berceta, north and east of La Spezia, Italy. T. uniflorum
seeds were collected at approximately 800 m elevation in the Pilion Mountains
just southeast of Neohori, Greece. It would appear that we confused the orig-
inally identified material as T. noricum with T. aanescens , but an exact iden-
tification cannot be made until flowering occurs.
f. patulum and T. pignantii were apparently not observed on this collec-
tion trip. Herbarium specimens of these two species would suggest that they
may be mistaken for T. medium and T. rubens . Examination of specimens of T.
patulum and pignantii collected in the early 1900’ s located in the National
Herbarium, Washington, D.C. provide evidence to support this similarity be-
tween these species.
While we attempted to maintain a rigid watch for the species listed in
the objective and even with the excellent guidance and assistance provided we
were disappointed in the actual number of collections made of the desired
154
species. Contact is being maintained with personnel in both Greece and Italy
who will continue the search. In addition, future trips should include Yugo-
slavia, if at all possible. For the best cooperation and assistance it is
recommended that such a trip be of mutual benefit to both countries. The past
trip was mutually beneficial in that many ideas, and in a few cases, germplasm
was shared by members of both countries.
SUMMARY
During the period of June 20 to July 26, 1977 thirty-seven species of the
genus Trifolium represented by 291 accessions were collected throughout Greece,
Crete, and Italy. In Greece and Crete collections were made from sea level to
elevations of 1800 meters. Samples were collected in the Menikion and Vermion
Mountains and the Khalkidhiki region in the Macedonia Province of Greece. In
Thessali Province samples were collected in the vicinity of Trikkila, Lake
Megthobas, the base of Mt. Olympus, and Pilion Mountains. Collections were
made in the Epirus Province near the border of Albania and in the vicinities
of Ioannina and Metsovan. Fourty-one samples were collected in the western
one-fourth of Crete. One hundred-one samples were collected along the eastern
slopes of the Appennino Mountains from near Bari to the Po Valley. One day
was spent exploring the Gargano area east of Foggia. The last three days of
travel were spent in the mountains northeast of Genoa traveling in a south-
easterly direction toward Rome. This latter region had the greatest diversity
of perennial Tri folium species of any area explored.
REFERENCES USED FOR IDENTIFICATION
Combe, D. E. 1968. Trifolium L. pp. 157-172. In Flora Europaea. Vol. 2
Edited by Tutin, T. G. , Heywood, V. H. , Burges, N. A., Moore, D. M. ,
Valentine, D. H. , Walters, S. M. , and D. A. Webb. Cambridge University
Press. Great Britain.
Fiori, Adriano, and Paoletti, Givliv. 1970. Flora Italiana Illustrata.
Edagricole.
Zohary, M. 1968. Trifolium L. pp. 384-448. In Vol. 3, Flora of Turkey.
Edited by P. H. Davis. Edinburgh University Press. Great Britain.
Zohary, M. 1972. A revision of Trifolium sect. Trifolium (Leguminisae) . II.
Taxonomic treatment. Candollae 27:99-158.
155
RECENT DEVELOPMENTS IN BREEDING AND SELECTION OF TROPICAL LEGUMES
(STYLOSANTHES) FOR THE DEEP SOUTH
by J. B. Brolmann
The first tropical legumes for use in Florida pastures were introduced
during the 1950' s. Extensive testing of many introductions, in pure stands
and in combination with grass, followed. Encouraging results have been
obtained with the genera Stylosanthes . Desmodium and Siratro (5).
Selection and breeding of warm-season legumes have been conducted in
Australia. Important selections from plants introduced from other areas of
the world were made in the 1950's and 1960's. Most of the introductions were
from South America where over 4,000 species of Leguminosae are found. The
most useful genera were Centrosema , Desmodium, Stylosanthes and Macroptilium.
The large diversity within Stylosanthes has made it possible for Australian
workers to make rapid progress (4) . Most commercial tropical forage legume
varieties in Australia have been a result of their very elaborate plant-
introduction program. A few varieties, such as Siratro (Macroptilium
atropurpureum) , however, were the result of their breeding program.
Growth of most tropical legume species suitable for forage is reduced by
cold weather. Frosts damages or kills vegetation. Frosts do not normally
occur until December in South Florida. Re-growth occurs with warm weather in
the spring. To bridge this gap in forage production, more cool-temperature-
tolerant warm-season legumes need to be developed. Obtaining plants with
cold or f rost-tolerance (from higher altitudes or greater latitudes in South
America) is of particular importance.
In south Florida, as in most sub-tropics, pasture growth is limited by
drought or flood at some time during the year. Development of varieties
which persist under these conditions is an important goal.
In Florida emphasis has been placed on selecting within the genus
Stylosanthes . This genus is found in both the wet and dry tropics. It grows
under various soil conditions and has large morphologic and genetic differ-
ences. The variability within Stylosanthes species is very desirable for
selection or breeding purposes. The group contains cross-pollinated as well
as self-pollinated species. Open-pollinated clones of S. guianensis produced
progeny yielding 3 to 4 times as much dry matter as progeny from self pollin-
ated clones (1). Selfing resulted in inbreeding depression in this case.
Some species like ,S. hamata are predominantly self-pollinating . Interspecific
crosses could serve as means of variety improvement. Natural hybrids occur-
ring in older field plots, the result of interspecific crossing, have been
found and are being evaluated.
Native Stylosanthes hamata occur on the east coast of Florida from
Jupiter south, on calcareous soils. There are a variety of ecotypes, includ-
ing diploids (2N=20) and tetraploids. Recent investigations indicate that
tetraploid S_ . hamata are more vigorous than diploids (2) . Tetraploids grow
at lower pH than the diploids. When tetraploids are open pollinated, natural
crosses with other species may occur in the field, sometimes producing vig-
orous interspecific hybrids. The F-2 consists of a great variety of types
which can be selected for desirable agronomic qualities. Breeding lines are
156
screened by various selection pressures for persistence under sub-optimal
conditions such as flooding and freezing. Flood tolerance of several
Stylosanthes sp . has been tested and results indicate that only a few access-
ions are tolerant to flooding. _S. erecta and some Stylosanthes hybrids will
tolerate flooding for several months under controlled conditions, but growth
is usually reduced (3) . Frost will kill top vegetation of all Stylosanthes .
Most accessions however, will regenerate from the crown. Some species like
S_ . erecta and S. macrocarpa will regenerate from roots after frost. One
accession of S^. macrocarpa and two accessions of S^. montevidens is survived
the severe 1976-77 winter in central Florida (26 nights with frost).
In field tests early flowering, low seed producing accessions of S.
guianensis when grown in Bahia were far more persistent than the late flower-
ing, high seed yielding ones.
The great diversity of types in the genus Stylosanthes offers a good
possibility of developing varieties for almost any tropical or subtropical
environment. Further testing of advanced breeding lines should be encouraged
in other areas of the south. The use of tropical legumes is still very
limited in South Florida. There is a growing interest, however, to extend
their use and to find varieties suitable for Florida conditions.
LITERATURE CITED
(1) Brolmann, John B. 1973. Progeny studies in Stylosanthes guyanensis
(Aubl.) SW. Proc . Soil and Crop Sci. Soc . Fla. 33:22-24.
(2) Brolmann, John B. 1978. The occurrence of Stylosanthes hamata L.
(Taub.) in South Florida and its potential as a pasture legume.
Florida Scientist 41 (suppl.) P. 3.
(3) Brolmann, John B. 1978. Flood tolerance in Stylosanthes a tropical
legume. Proc. Soil and Crop Sci. Soc. Fla. 37 (in press).
(4) Edye , L. A., R. L. Burt, W. T. Williams, R. J. Williams, and B. Grof .
1973. A preliminary agronomic evaluation of Stylosanthes
species. Austr. J. of Agr. Res. 24:511-525.
(5) Kretschmer, Albert E., Jr. 1968. Stylosanthes humilis, a summer grow-
ing, self-regenerating, annual legume for use in Florida
pastures. Fla. Agr. Exp. Sta. Circ. S-184, 21 pp .
157
CONTRIBUTORS
Barnett, 0. W., assistant professor. Department of Plant Pathology and Physio-
logy, Clemson University, Clemson, SC 29631
Blaser, R. E.s professor, Department of Agronomy, Virginia Polytechnic Institute
and State University, Blacksburg, VA 24061
Bledsoe, B. L., professor. Department of Agricultural Engineering, P.0. Box 1071,
University of Tennessee, Knoxville, TN 37901
Brolmann, J. B., assistant professor, University of Florida, IFAS, Agricultural
Research Center, Fort Pierce, FL 33450
Busbice, T. H., professor, Crop Science Department, North Carolina State Univer-
sity, 1126 Williams Hall, Raleigh, NC 27607
Cope, W. A., professor, Crop Science Department, North Carolina State University;
Raleigh, NC 27607
Ely, L. 0., assistant professor, Department of Animal Science, Georgia Agricul-
tural Experiment Station, Experiment, GA 30212 (Teleg. and Exp. address,
Griffin, Ga.)
Gibson, P. B., research agronomist, Department of Agronomy and Soils, Auburn
University, Auburn, AL 36830
Haaland, R. L., assistant professor, Department of Agronomy and Soils, Auburn
University, Auburn, AL 36830
Harris, Barney, Jr., professor, Department of Dairy Science, 203 Dairy Science
Building, University of Florida, Gainesville, FL 32611
Hodges, E. M. , professor, Department of Agronomy, Agricultural Research Center,
Ona, FL 33865
Holt, E. C., professor. Soil and Crop Sciences, Texas A&M University, College
Station, TX 77843
Hoveland, C. S., professor. Department of Agronomy and Soils, Auburn University,
Auburn, AL 36830
Kalmbacher, R. S., professor. Department of Agronomy, University of Florida,
Agricultural Research Center, Box 248, Ft. Pierce, FL 33450
Knight, W. E., research agronomist, Plant Science Laboratory, Science and Educa-
tion Administration, Mississippi State University, Mississippi State, MS
39762
Kretschmer, A. E., Jr., professor, Department of Agronomy, University of Florida,
Indian River Field Station, P.0. Box 507, Ft. Pierce, FL 33450
Langford, W. R. , agronomist, Science and Education Administration, Plant Intro-
duction Station, Georgia Station, Experiment, GA 30212
McLaughlin, M. R. , visiting assistant professor, Department of Plant Pathology
and Physiology, Clemson University, Clemson, SC 29631
Mertens, D. R. , associate professor, Department of Animal Science, University of
Georgia, Athens, GA 30602
Mislevy, Paul, associate professor, Department of Agronomy, Agricultural Research
Center, Ona, FL 33865
Moore, J. E. , associate professor. Department of Animal Science, Nutrition Lab.,
University of Florida, Gainesville, FL 32611
Ocumpaugh, W. F., assistant professor, Department of Agronomy, 2183 McCarty Hall,
University of Florida, Gainesville, FL 32611
Peterson, H. L. , associate professor, Department of Agronomy, Mississippi State
University, Mississippi State, MS 39762
Quesenberry, K. H. , associate professor, Department of Agronomy, 2183 McCarty
Hall, University of Florida, Gainesville, FL 32611
158
Riewe, M. E., associate professor, Texas A&M University Agricultural Research
Station, Angleton, TX 77515
Ruelke, 0. C., professor, Department of Agronomy, 2183 McCarty Hall, University
of Florida, Gainesville, FL 32611
Schank, S. C., professor. Department of Agronomy, 2183 McCarty Hall, University
of Florida, Gainesville, FL 32611
Smith, R. L., associate professor. Department of Agronomy, 2183 McCarty Hall,
University of Florida, Gainesville, FL 32611
Smith, R. R. , associate professor. Science and Education Administration, Depart-
ment of Agronomy, University of Wisconsin, Madison, WI 53706
Taylor, N. L., professor. Department of Agronomy, Agri. Sci. Bldg. N. , Univer-
sity of Kentucky, Lexington, KY 40506
Watson, C. E., Jr., assistant professor. Department of Agronomy, Mississippi
State University, Mississippi State, MS 39762
Welty, R. E., professor, Department of Plant Pathology, North Carolina State
University, Raleigh, NC 27607
Wolfe, J. A., party leader, Soil Conservation Service, U.S. Department of Agri-
culture, P.0. Box 248, La Belle, FL 33935
159
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