RED CLOVER IN THE
"TWENTY-FIRST" CENTURY
R.R. Smith
INTRODUCTION
Red clover (Trifolium pratense
L.) is one of the leading forage legumes in the U.S., Canada, and northern and
eastern Europe. Red clover has maintained a prominent roll in animal agriculture
in the more temperate regions of the world due, in part to high seedling vigor,
ease of establishment, rapid growth, excellent soil improvement
characteristics, high forage quality and reasonably high yield. Records would
indicate that it was first cultivated in Europe in the third and fourth
centuries, recorded as being in Italy by 1550, in England by 1645, and in the
United States by 1663 (Taylor and Quesenberry, 1996). The early settlers
brought red clover to the US as it was an excellent feed source for their
animals. As settlement moved throughout the nation red clover moved with it.
Being adapted to temperate climates, red clover was and is used most
prominently in the northeastern and northcentral regions of the US, and
southeastern Canada for hay, silage, grazing and soil improvement. Use of red
clover declined substantially beginning in the 1950s as alfalfa (Medicago
sativa L.) became more prominent forage for hay and silage. Nationwide, red
clover and grass mixtures declined from approximately 15 million to 12 million
acres between 1950 and 1970, and based on seed disappearance they probably
declined to about 11 million acres by 1987. However, with the increase amount
of grazing over the past decade the use of red clover has increased (Taylor and
Smith, 1995).
I would like to briefly review some
of the progress made over the past five decades, report on the results of some
current research, and speculate what one might expect to see (or what might be
needed) in red clover improvement and use in this century.
IMPROVEMENT IN RED CLOVER OVER THE PAST
FIVE DECADES
In Wisconsin and other parts of the
U.S. red clover has long been considered to be a short-lived perennial.
Environmental stress and root rot diseases contribute to the lack of
persistence of red clover (Taylor and Smith, 1979; Smith and Kretschmer, 1989;
Venuto et al., 1992). Of the root rot causing pathogens of red clover,
organisms of the Fusarium species have been isolated most consistently
from diseased roots (Kilpatrick et al., 1954; Chi, 1965; Velde, 1980; Leath,
1985). The foliar disease, northern anthracnose, caused by Aureobasidum
caulivora (Kirchn.) W.B. Cooke, is endemic and causes severe forage
loss during the first growth of the season. Therefore, resistance to these
pathogens should lead to improved persistence and yield. Selection for plant
longevity in older stands of red clover and the incorporation of genes for
resistance to root rot pathogens are the most practical methods of improving
persistence of red clover (Smith, 1983; Venuto et al., 1992).
Earlier (Smith, 1998) I reported to
you on the improvement the USDA - Agricultural Research Service - University of
Wisconsin project has made in red clover through selection for persistence and
disease resistance since the 1950s. Let us regress a minute and review that
information. The result of repeated selection over that period for persistence
and disease resistance has been the release of better cultivars: Lakeland
released in 1953, Arlington in 1973 (Smith, et al., 1973) and Marathon in 1987
(Smith, 1994). Both forage yield and resistance to root rot and northern
anthracnose has been improved (Figure 1). Resistance to the two diseases, root
rot and northern anthracnose, has steadily increased with the development of
new germplasm. Two to three cycles of selection for resistance to northern
anthracnose was applied during each cycle of selection for persistence. On the
other hand, only one cycle of selection for root rot occurred after the third
cycle of selection for persistence. Earlier improvement in root rot resistance
was the result of natural selection for resistance with the selection of
healthy, persistent plants. Total forage yield increased over the cycles of
selection due, in part, to selection for disease resistance and to increased
persistence. There was no difference in forage yield (1.9 Tons Dry Matter per
Acre) among the populations developed over the four decades in the second year
of production (Figure 2). The differences among the populations occurs in the
third and fourth year of production with Marathon and Wis Exp producing
excellent forage yields in these latter years of production. Selection in
exiting 3- and 4-year old stands of yield trials has been effective in
improving persistence and to some extent root rot resistance. Similar results
for forage yield have been observed in the red clover varieties developed by
private companies (Figure 3).
Red clover cultivars on the market
today are superior to those available two decades ago. Stand longevity, forage
field, and disease resistance has been improved. Current germplasm being
developed by the public and private programs appear to be even superior to
those on the market today. So you might expect to see better, more persistent
cultivars in the future. In our USDA/ARS - University of Wisconsin program we
have the next generation of germplasm ready to be released as either germplasm
or cultivars (Figures 2 and 3 - Wis Exp). Other germplasm lines with resistance
to the root-knot nematode, Aphanomyces, Fusarium and Mycoleptodiscus
are ready for release.
EVALUATION OF RED CLOVER CULTIVARS
WITH GRASSES
Red clover is most often grown with
companion grass for hay, silage or grazing. However, little information is
available on the performance of cultivars in competition with grass species.
Smith and Sharpee (1992) suggested that the relative performance of red clover
cultivars may not be similar when grown in monoculture vs. in competition with
grass.
The object of this research was to
evaluate current, persistent red clover cultivars when grown with a grass
companion using two harvest management systems. The research was conducted in
cooperation with Dan Wiersma, Assist. Superintendent, Marshfield Agricultural
Research Station and Mike Mlynarek, Superintendent Ashland Agricultural
Research Station, College of Agricultural and Life Sciences, University of
Wisconsin. The research has been reported at the 1999 Annual Meetings of Crop
Science Society of America in Salt Lake City, UT in Nov. 1999 (Wiersma et al.,
1999).
Eleven cultivars or experimental
strains (Entries 1 through 11) were evaluated with or without bromegrass (Bromus
inermis) at Arlington, WI or timothy (Phleum pratense) at Marshfield
and Ashland, WI. The entries were subjected to two harvest management systems
(2-cut or 3-cut per year) at Arlington and Marshfield and one (2-cut) at
Ashland, WI. Seeding rates were 6, 3, and 3 lbs per acre for clover, timothy,
and bromegrass, respectively. Plots were harvested when red clover reached 20%
bloom for the 3-cut harvest system and 40% for the 2-cut system. To determine
botanical distribution in the clover-grass mixtures, two 40 x 40 cm samples per
plot were taken just prior to harvest. Yield of clover and grass was determined
as % clover or grass times total plot dry weight. Plots were established in
May, 1996 and data collected in 1997 (2nd year), 1998 (3rd year), and 1999 (4th
year).
As expected, the yield of clover
grown without grass was, in general, greater than when grown with grass,
although the total grass-clover yields was greater. Both at Arlington and
Marshfield the 3-cut system produced more red clover whether grown with or
without grass than the 2-cut system (Figure 4.). However, the 2-cut system
produced more red clover than the 3-cut system in the fourth year of
productions at all locations. The decline in red clover production over time
was less drastic in the 2-cut system.
The performance of red clover
cultivars was influenced by the location, the cutting system, and the presence
or absence of grass. In general, the performance of the cultivars grown without
grass did not predict the corresponding response when grown with grass. Of the
15 possible comparisons of the performance of the cultivars with and without
grass only one was significant (Table 1: at Arlington under the 3-cut system in
the 3rd year). In fact, this significant correlation, -0.64, was in the
opposite direction than expected. If performance in pure stands (without grass)
is going to predict performance with grass the correlation should be positive
and high (greater that 0.62 but less than 1.00). Examples of this lack of
correlation between cultivar yields when grown with and without grass can be
observed in Figures 5, 6, and 7.
From these results it would appear
that red clover cultivar performance in the absence of grass competition was
not indicative of their performance when grown with grass competition. Future
selection of red clover cultivars should be done in the management system that
are similar to the system used by the growers.
RED
CLOVER OF THE FUTURE
It has been long recognized that
red clover is an excellent forage legume for hay, silage, and grazing. As
indicated earlier, the use of red clover in the US has declined over the past
100 years from about 30 million acres in the early 1900s to about 11 million by
1987. This decline in use has primarily been due to low nitrogen fertilizer
prices, an increase use of alfalfa, a decrease in legume-grain row crop
rotations, and the short-life of the plants. However, since the 1980s the use
of red clover has stabilized, if not increased somewhat. This has been due to
the development of improved, persistent, disease resistant cultivars; the
recognition of its value in grazing conditions; and an increased recognition of
its importance in crop rotations and soil conservation. Recent research has
identified chemical compounds in red clover, some of which are important in
protein utilization, others in animal reproductive processes, and still others
as pharmaceutical products. Therefore, the use of red clover will continue to
occupy a position of major importance in US agriculture.
Improvement in
Agronomic Characteristics
Disease resistance and
persistence: Even though current cultivars have good disease resistance and
are relatively persistent, continued improvement in these attributes is needed.
Lack of resistance to the soil-borne Fusarium pathogens is one of the
leading causes of stand failure in red clover. Some improvement has been made
in this direction, but further, concentrated efforts are needed and should be
rewarded with even a greater degree of persistence in the crop.
Crown position and root
structure: Unlike alfalfa and some other forage legumes where the crown of
the growing plant is positioned just below the soil surface, the crown of red
clover is positioned at the soil surface. This exposes it to a greater degree
of environmental stresses such as temperature, disease organisms, physical
abuse, etc. Developing red clover cultivars where the crown is position just
below the soil surface would give greater protection against these stresses and
undoubtedly lead to increased persistence. Initially red clover produces a
primary tap root, but as it is exposed to diseases and other stresses it gives
way to a secondary, branching system that develops reasonably close to the soil
surface. Types need to be identified that have a disease tolerant tap root
structure with an extensive secondary system. Rhizomes, underground stems, have
not been observed in the red clover species, however, related species do have
such structures. Efforts need to be extended to interspecifically transfer,
through molecular or other techniques, this desirable attribute. Incorporation
of the rhizome structure would enhance persistence and improve drought
tolerance in the species.
Grazing tolerance and grass
competition: Red clover is being used extensively for grazing and most
often is grown with a companion grass whether grazed or used for hay or silage.
Very little effort has been expended to develop red clover cultivars that are
adapted to these conditions. As mentioned earlier in this report the
performance of red clover cultivars in monoculture is not indicative of their
performance when grown with grass companion crops. It is presumed that this
would be true whether used for grazing or otherwise. A major component of any
future red clover genetic and breeding projects should include the development
of germplasm tolerant to these uses.
Chemical
Attributes and Quality Improvement
Protein utilization and
protection: Papadopoulos and McKersie (1983) reported that red clover has
90% less proteolysis than alfalfa during ensiling. Also, Albrecht and Muck
(1991) report ensiled red clover yields 30 to 40 % less non protein nitrogen
(NPN) than ensiled alfalfa. If proteolysis and NPN formation can be reduced,
then forage protein utilization by the ruminant animal should be improved.
Jones et al. (1995) report that this effect in red clover is the result of the
polyphenol oxidase (PPO) enzyme system in red clover that inhibits activity of
the plant's proteases in the silo. Among the forage legumes this PPO enzyme
system is unique to red clover. This important attribute in red clover should
be exploited by either genetically increasing its activity in red clover or
genetically transferring the attribute to alfalfa and other legumes or both.
Phytoestrogens: Red clover
contains high levels of phytoestrogens which have been reported to interfere
with normal reproduction in sheep. Although no documented reports have been
recorded for dairy cows it remains that this may present a problem, especially
for grazing cows. The oestrogenic compounds are isoflavones which include
formononetin, diadzein, genistein, and biochanin A (Cox and Braden, 1974). Formononetin
(7-hydroxy-4'-methoxyisoflavone) is recognized as the most important of these
oestrogenic compounds in red clover (Morley et al., 1966, 1968). Selection for
lower levels of formononetin in red clover has been effective (McDonald et
al.,1994). The authors report improved fertility of ewes grazing the low
formononetin red clover. Since red clover is being used extensively in grazing
conditions, red clover cultivars with low levels formononetin need to be
developed. Contrastingly, dietary compounds, Promensil, with high estrogenic
activity are being market as a supplement in human diets to combat PMS and
osteoporosis.
Pectic polysaccharides and
forage quality: While protein content in most forage legumes is quite high,
the full potential of the protein, especially the leaves, is not realized due
to rapid degradation rates and conversion to ammonia in the rumen. Numerous
schemes to alter the proteins of forage legumes range from chemical to physical
treatments to actually genetically altering the plant to produce proteins more
resistant to degradation (Broderick et al., 1991). An alternate strategy to
improve utilization of plant protein would be to match the rapidly degraded
protein with an equally rapidly degraded carbohydrate (RDC) source such that energy
would not be limiting to rumen microbes (Stokes et al., 1991). This assures
that the plant protein would be efficiently converted to microbial biomass
benefiting the ruminant. Pectic polysaccharides (commonly known as pectins)
represent a potential source of RDC , and a significant portion of the total
structural polysaccharides in forage legume cell walls are pectic materials.
Thus, increasing the cell wall pectic polysaccharide (pectin) content of forage
legumes would improve utilization of their nutritional potential. Earlier
research has shown that genetic variability exists in red clover for cell wall
pectin concentration (Hatfield and Smith, 1995). Divergent populations of red
clover and other forage legume germplasm with a range of cell wall pectin
concentration are needed to assess the actual impact of increased plant pectin
on forage quality and animal performance.
CONCLUSIONS
Red clover cultivars on the market
today are superior to those available two decades ago. It is expected that you
will see better, more persisten cultivars in the future. The next generation of
red clover germplasm developed in the USDA/ARS - University of Wisconsin
program is ready to be released as either germplasm o rcultivars. However,
future selection of red clover cultivars should be done in the management
system that are similar to the system used by the growers. The prominence of
red clover in US agriculture should remain high, if not increase, as you see
new cultivars and uses of the crop. Because of its unique qualities of high
seedling vigor, excellent forage quality, ease of establishment,
competitiveness with grass and importance to soil conservation you should see
red clover continuing to play a major roll in world agriculture.
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