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POTENTIAL FOR REPLACING
NATURALIZED WEEDS IN CALIFORNIA'S
ANNUAL GRASSLANDS WI'IH SELECTED
MEDITERRANEAN SPECIES: PLANT
EXPLORATION ANDJMANAGEMENT
CONSIDERATIONS
Walter L. Graves
Melvin D. Rumbaugh
Wesley M. Jarrell
ABSTRACT
Grasslands and associated grassland vegetation types
(Hardwood/Savannah, Shrub/Chaparral) represent 15
million ha (37 million acres); more than one-third of
California's total land area of 41 million ha (100 million
acres). Improvement of this vegetation plant cover would
minimize soil erosion, restore depleted soil organic matter,
and help sustain the multiple use of this natural resource.
Soils in California's annual grasslands usually are deficient in nitrogen and thus limit plant use of available moisture. Nitrogen fertilizers were used to correct this deficiency, but this practice became unprofitable in the late
1960's. Nitrogen fertilizer is manufactured from natural
gas, a fossil fuel. Following the energy crisis of 1973 and
the Middle East situation of 1990, application of nitrogenous fertilizers to grasslands became impractical (Green
1978).
Another approach to improving nitrogen levels in these
soils is the establishment of nitrogen-fixing legumes. Annuallegume adaptation and management research has
been carried out in the California annual grasslands since
the 1940's. Early work by Williams and others (1956) and
Jones and Evans (1960) established the need for adequate
levels of soil phosphorus and sulfur and timely grazing to
establish and maintain annual subclover (Trifolium subterraneum L.) and rose clovers (Trifolium hirtum All.). This
work was further fine-tuned in the 1960's to develop competitive and effective Rhizobium strains needed for subclover establishment and persistence in many of California's
annual grassland soils (Jones and others 1978).
The 1960's also saw the development of herbicide technology to control weed competition and aid annual legume
establishment in grasslands (Kay 1964; Kay and McKell
1963; Murphy and others 1962).
Murphy and others (1973) summarized the state-of-theart of establishment and management of annual legumes
on California's annual rangelands in the early 1970's. In
recent years, research emphasis on improving annual
rangeland productivity with annual legumes has concentrated on intensive animal management schemes and adjustment of P and S fertilizer inputs (Demment and others 1987; Jones and others 1990; Phillips and others 1987;
Raguse and others 1988).
California's annual grasslands developed under a
Mediterranean climate with variable winter rainfall and
long, dry, warm summers. These grassland associations
are now dominated by aggressive, adventive, low-quality
forage annuals introduced from the Western Mediterranean
region. A program was initiated to introduce and select desirable Mediterranean forage legumes adapted to California
and to develop management strategies appropriate for their
use. The important factors are introduction and evaluation
ofa large number of accessions, matching the legume host
with a specific and efficient Rhizobium strain, adequate soil
phosphate and sulfur levels, appropriate and timely grazing management, and minimum tillage and selective herbicides if used in pasture rotations with dryland cereals.
INTRODUCTION
California's grasslands have evolved under a
Mediterranean climate with a highly variable winter
rainfall and long, dry, warm summers (Burcham 1982;
Woods 1976). Aggressive exotic annual species began to
replace the native plants in these grasslands and associated vegetation types following the introduction of livestock and crops from Western Europe and North Africa
(Baker 1989; Burcham 1982). These grassland associations are now dominated by the introduced annuals. Although the alien species are opportunistic and produce
quality forage during very short late-winter to spring
periods when moisture and temperature conditions are
optimal for growth, their mature forage is of poor quality
(Murphy and others 1973).
Paper presented at the Symposium on Ecology, Management, and Restoration of Intermountain Annual Rangelands, Boise, ID, May 18-22, 1992.
Wolter L. Graves is Area Form Advisor for Natural Resources Management, University of California Cooperative Extension, Son Bernardino
County, 777 E. Rialto Ave., Son Bernardino, CA 92416; Melvin D.
Rumbaugh is Research Geneticist, USDA Agriculture Research Service,
Utah State University, Crops Research Laboratory, Logan, UT 84332;
Wesley M. Jarrell is Research Scientist, Oregon Graduate Institute of Science and Technology, 19600 N.W. Von Neumann Drive, Beaverton, OR
97006-1999.
37
While the introduction of annual legumes adapted to a
Mediterranean climate and capable of biologically fixing
significant amounts of nitrogen is promising, they are not
being used on a large scale in the lower and less dependable rainfall regions of central and southern California.
The establishment success of imported Australian cultivars, particularly subclovers, has been erratic. California's
rainfall amounts and distribution are less dependable than
in Mediterranean climate areas of Australia where annual
legumes are commonly used (Graves and others 1991).
The naturalized annual legume, bur medic (Medicago
polymorpha L.), became an alternative host for the alfalfa
weevil (Jlyperia brunneipennis) following its introduction
as a pest on irrigated alfalfa (M. sativa) in the Central
Valley. This weevil caused the decimation ofbur medic
in much of the pasture area of the dryland grain-pasture
rotation system on the west side of the Sacramento Valley. After the elimination ofbur medic, the soils of this
system also became nitrogen deficient and regular applications of expensive nitrogen fertilizer are now needed
to make this dryland grain-nonlegume annual grassland
pasture rotation system productive (Graves and others
1987).
Australian scientists and land managers developed techniques to displace i~troduced annual plants of poor forage
quality with more desirable forage legumes, primarily subclover and annual medics (Medicago sp.) (Crawford and
others 1989; Reed and others 1989).
The Australian use of annual legumes in pastures in
rotations with cereals, called "Ley Farming" in Australia,
has been extensively reviewed by Puckridge and French
(1983). An excellent review of subclover-based pasture establishment and management in Western Australia also
is found in the 1983 issue of the Journal ofAgriculture of
Western Australia (Gillespie and others 1983).
Since the widespread sowing of subclovers in the 1920's
and annual medics in the 1930's, the Australian experience in establishing and managing some 40 million ha
(99 million acres) of annual legumes emphasizes the importance of the correct legume-Rhizobium association, cultivar
screening and selection, macro and micro soil nutrients
availability, grazing management to control undesirable
weedy species, and the use of selective herbicides and
shallow tillage in pasture-dryland cereal rotations (Carter
1987; Crawford and others 1989; Reed and others 1989).
In recent years, factors affecting legume seed bank ecology have received considerable attention. Maintaining
optimum levels of seed reserves of target legume species
is important for long-term persistence and productivity
(Carter 1989).
The Australian pasture legume researchers make a
strong case for the value of the accidental introductions
into Australia, in the 19th century, of annual legumes
from countries bordering the Mediterranean Sea (Cocks
and others 1979; Gladstones 1966, 1967).
They continue to emphasize Mediterranean region
plant exploration programs to search for better adapted
and more persistent legume germplasm (Crawford 1983;
Crawford and others 1989; Francis and Gladstones 1983).
Although Australian and California annual legume establishment and management technology have similar historical development patterns and common principles and
practices, we do have one important difference-California
was not blessed with opportune accidental introductions
of annual legumes other than the weevil-susceptible bur
medic. Until recently, we had not thought it necessary to
conduct plant explorati~ns to the Mediterranean regions
to improve our annual legume germplasm base. Instead,
we depended heavily on the Australian cultivar development and seed production program to meet our annual
legume introduction needs.
The USDA National Plant Introduction Program was
initiated in 1898. However, by 1979 only a very limited
number of annual legume introductions that performed
well in California's annual grasslands had been acquired
(White and Oakes 1979). Although preliminary annual
legume testing and evaluations by Graves and others
(1980) in southern California in the 1970's demonstrated
that there was a potential for more extensive annual legume use in this area, the cultivars available to us at that
time did not seem to possess persistence characteristics
suited to our highly variable annual rainfall pattern.
While the Australian cultivars were not adapted to our
environment, the principles used in the Australian plant
exploration and selection programs seemed to be worthy
of consideration. We needed to develop our own plant exploration program to target climatic analogs and search
for annual legume ecotypes that had evolved and persisted
under similarly harsh conditions. The 1980's saw this goal
achieved and our hypothesis tested. This plant exploration
program is covered in more detail in Graves and others
(1987 and 1991) and Rumbaugh and Graves (1985).
It is the objective of this paper to report on the field testing of these annual legume introductions from our plant
exploration and exchange program with Mediterranean
collaborators and the adaptation of this plant material
to the annual grasslands of southern California.
FIELD TRIALS
Oak-Annual Grassland (Savannah) MiddleElevation Site-This evaluation of annual legume introductions from our 1983 plant exploration program
in Morocco (Rumbaugh and Graves 1985) was initiated
in the fall of 1984. It included accessions that we had targeted as originating in zones of similar climate pattern.
The trial consisted of20 entries of 11 wild subclover accessions native to Morocco, four Australian subclover cultivars,
three naturalized rose clovers from northern California,
and two Australian rose clover cultivars. The test site
is located in San Diego County at 975 m (3,200 ft) in a
600-mm (23.6-inch) September 1 through May 31 effective
seasonal rainfall zone. Details of the materials and methods and site characteristics have been reported and the
evaluations for the first 4 years of testing summarized
(Graves and others 1991).
The significance of persistence evaluation in this zone
is the lack of success of annual legume establishment and
the fact that a somewhat long drought and poor rainfall
distribution period occurred over a 5-year span from the
1986/87 season through the 1990/91 season. Plots were
located in an open range pasture and were not fenced to
exclude grazing. The pasture with the test plots received
continuous moderate grazing by cattle during the late
38
winter and spring growing seasons in the establishment
year and throughout the duration of the 8-year evaluation
period. Stand cover evaluations were made each spring
near the end of the growing season by visually rating plot
cover on a 0-10 scale (0 =no plants, 10 =complete ground
cover of the seeded plot). Stand regeneration was defined
as the annual clover's ability to regenerate its cover within
the planted plot of 1.45 m 2 (16 ft2). The most recent stand
persistence evaluations were made on April 24, 1992. Flowering also was recorded on the date of the 1988 stand ratings. Stand regeneration data were analyzed statistically
for strain differences.
Annual Grasslands-Lower Elevation Site-It is believed that hardseededness may be the most important
characteristic that an annual legume may possess in order
to persist in a highly variable rainfall region such as that
found in southern California. Smith (1988) pointed out the
importance of hardseededness as an adaptation and survival mechanism in the highly variable rainfall patterns
characteristic of Mediterranean climates. The need to
screen and breed for hardseededness in subclover was recognized in Australia (Francis and Gladstones 1983) and
in Spain (Gomez Pitera and Ramos Monreal1980) as an
important component of persistence in areas of 375 mm
(15 inches) or less rainfall and for successful stand regeneration after cereal cropping.
Gomez Pitera and Ramos Monreal (1980) screened
more than 2,000 subclover lines from southern Spain for
hardseededness, estrogen levels, and seed production, and
a small number of the superior lines from this research
were sent in the fall of 1979 to the University of California,
Davis, for seed increase and field evaluations. Seven of
these subclover lines of Spanish origin (Spanish Forage
and Pasture Research Institute, Badajoz numbers: 1142,
59,245, 92, 312-A, 704 and 393) of high hardseededness
were increased by Burgess Kay, wildlands reseeding specialist, at the Department of Agronomy and Range Science,
University of California, Davis, during the spring of 1980
and distributed for field trials during the fall of 1980. During the 1980 to 1982 period these Spanish lines were established in annual grassland locations in San Diego and
San Luis Obispo Counties. Medium-term evaluations were
made on five lines in the spring of 1987 (Graves and others
1991).
An additional trial with the seven Spanish lines was
initiated near the town of Alpine in San Diego County in
the fall of 1982, with the objective of evaluating long-term
persistence. This test site is located at 714 m (2,345 ft),
some 53 km (33 mi) inland to the east of the San Diego
coast. The location is in the inland foothill climate zone
with a mean annual rainfall of 450 mm (18 inches). The
soil is a Wyman (fine-loamy, mixed, thermic, Typic Haploxeralfs) soil with neutral to slightly acid pH, loam to clay
loam texture, 2-5 percent slope, and with low nitrogen,
phosphorus, and organic matter levels. The site is classed
as annual grassland and has been used for livestock grazing since the late 1800's. The site is dominated by filaree
species CErodium sp.), annual bromes CBromus sp.), and
foxtail fescue (Vulpia myros [L.] K.C. Gmelin var. hirsuta
Hack).
The seven Spanish lines and three early maturing hardseeded Australian subclover cultivars (Nungarin, Geraldton,
and Daliak) were seeded on November 24, 1982. Single
superphosphate (0-18-0-12) was applied by broadcasting
at the rate of 300 kglha (277 lblacre) prior to seeding. One
hundred seeds of each of the entries were planted 8 mm
(0.33 inch) deep in 1.20-m (4-ft) single-row plots (no-till)
arranged in a randomized block design, replicated four
times. All seeds were freshly pellet-inoculated at the rate
of 5 kg of inoculant per 100 kg of seed (Pelinoc inoculating
system, Milwaukee, WI).
The pasture containing the trial received continuous,
moderate-to-heavy grazing by cattle during the winterspring growing season for the 10-year evaluation period.
Plant stand evaluations were made April 6, 1983, to verify
first-season establishment (by visually rating row cover on
a 0 to 10 score (0 =no plants, 10 = complete coverage of the
row). Stand persistence evaluations were made at the end
of the tenth growing season, (April 24, 1992) to measure
the subclover lines' long-term ability to regenerate following low rainfall (drought) years stress. Initial plant and
1992 plant stand persistence evaluations were analyzed
statistically for strain differences.
OAK-GRASSLAND RESULTS
The results from this trial are most encouraging (table 1).
Following the long 5-year drought from 1987 through 1991,
three of the Moroccan subclovers regenerated and one experimental accession, GR 508 (PI 517171), was significantly
(P < 0.05) superior to all other entries including the rose
clover cultivars and the northern California naturalized
lines. None of the Australian subclover cultivars, Seaton
Park, Northam, Geraldton, or Nungarin, persisted. These
results confirm the difficulty that we have had with the
establishment and persistence of Australian subclover cultivars in this southern California zone.
The Australian rose clover cultivars, Hykon and Kondinin,
continue to show some degree of persistence, as did the naturalized collections from Mendocino, Shasta, and Siskiyou
Counties. These three naturalized rose clover accessions
are much later in maturity than the superior subclover accessions and the two rose clover cultivars, and we would
expect these naturalized northern California lines to be at
a disadvantage in this zone due to its short rainfall season.
Thus, we would not expect the accessions to persist or, at
best, to regenerate only during years of above-average
rainfall.
Considering that rainfall was 25 to 40 percent below
average during this 5-year-long drought period (1987 to
1991), the test results are indicative of adaptation to the
extreme stress conditions of this zone. At least one of the
three persistent Moroccan accessions, GR 508 (PI 517171),
has demonstrated the potential for long-term regeneration
and adaptation to this annual grassland type of southern
California.
ANNUAL GRASSLAND RESULTS
After 10 seasons, including 5 drought years from 1987
through 1991, Spanish experimental accession 1142 was
significantly (P < 0.05) superior in stand persistence to all
the other accessions, including the Australian cultivars
(table 2). These results follow the pattern and confirm the
findings as reported by Graves and others (1991) who used
39
Table 1-5ubclover (sub) and rose clover entries regeneration and flowering evaluations at the Alford Ranch, Mesa Grande, San Diego County. at the end of
fourth and eighth growing seasons
Ranking/plot
coverage1
Fourth season
Eighth season2
Variety/
accession
GR 508 Sub (PI517171)
GR 565 Sub (PI 517173)
GR 567 Sub (PI517174)
Shasta 4300' Rose
Kondinin Rose
Siskiyou Rose
Mendocino Rose
Hykon Rose
Seaton Park Sub
Northam Sub
GR 435 Sub (PI517164)
Geraldton Sub
GR 448 Sub (PI 517167)
GR 450 Sub (PI517168)
GR 316 Sub (PI517155)
GR 436 Sub (PI517165)
GR 494 Sub (PI 517170)
GR 519 Sub (PI517172)
Nungarin Sub
GR 301 Sub (PI 517154)
Flowering on
3/29/8&3
8.8
6.2
72
3~
+
+
~2
+
a2
5.8
5.0
5.0
3.0
2.0
2.8
25
2.0
0
0
0
0
0
0
0
0
5~
4.5
4.2
3.5
3.2
2.2
2.0
1.8
1.8
1.8
1.2
1.2
1.2
1.0
+
+
+
+
+
+
+
0
+
0
0
0
+
+
1.5
LSD (0.05)
of four repetitions (0 • no plants, 1o• complete coverage of plot).
of variance calculation did not Include entries that did not persist; •o• (zero) ratings.
.. flowers;- .. no flowers).
1Average
2Analysis
3 (+
Table 2-5panlsh and Australian subclover stand establishment, 1Oth-yr persistence,
and flowering maturity date at the Alpine, San Diego County, site
Straln/cultlvar
59
312-A
245
393
92
704
1142
Geraldton
Daliak
Nungarin
LSD (0.05)
1Average
Stand establishment
on 4/6/831
Stand persistence
1Oth yr, 4/24/921
Flowering
maturlty2
7.5
7.5
7.2
7.0
6.8
6.8
6.0
7.0
7.0
7.0
1.8
0
0
2.0
0
1.8
5.5
2.8
0
3.0
+3
+6
+3
+3
+3
+2
+3
+3
+3
0
0.8
~.1
(4)
of four repetitions (0 • no plants, 10 • complete coverage of the plot row).
2 (Weeks after Nungarin) Nungarin Is considered earliest of trial entries.
3Analysis of variance calculations did not Include entries that did not persist;
4Average
of observations, no statistics completed.
these same lines in other localities. The lack of persistence
of the Australian cultivar Daliak confirmed the inability of
this cultivar to adapt to the harsh conditions of southern
California.
The stand establishment ratings showed that most of
the trial entries were similar in ability to establish the
first year from the initial seeding. However, Spanish line
1142 showed a significantly lower plant stand (P s 0.05)
·o· (zero) ratings.
than any of the other experimental lines or Australian
cultivars. Yet, by the end of the lOth season, this line
was the only trial entry that was regenerating at a desirable level of greater than 40 percent cover. The point to
be made here is that under unfavorable and stressful climatic conditions there is a need for long-term evaluation
trials to allow adaptability characteristics to express
themselves.
40
We assume that early flowering gives the annual legumes
an added adaptability advantage in escaping drought stress
in low rainfall years; however, we can see from the poor
showing of the Nungarin cultivar, the earliest flowering
entry, this extreme early flowering characteristic is not the
most important factor in helping the plant to persist in
these conditions.
While our results did not all9w us to choose between
Spanish lines 1142 and 59 on the basis of other agronomic
traits, this long-term trial does allow us to select line 1142
as the most persistent in the annual grassland zone of
southern California.
Gomez Pitera and the Servicio de Investigacion Agraria
Spain, for seeds of the Spanish lines; Burgess
Kay, Range Science Specialist, UCD for assistance in seed
increase; our rancher cooperator, Spike Alford, of Mesa
Grande; the resource management personnel of the Palomar
District of the Cleveland National Forest; Henry Adams,
USDA-SCS Range Specialist, San Diego County; and last
and especially all our North African colleagues and friends
who provided us guidance, encouragement, and shelter to
undertake these plant exploration adventures in pursuit
of rapidly disappearing legume germplasm from a region
of extremely high-use pressures.
SUMMARY
REFERENCES
These long-term persistence evaluations provide a very
exciting example of the successful collection and introduction of wild-type annual legumes from native habitats in
the Mediterranean region. We believe that our hypothesis
of expecting to find wild types of annual legumes in analogous climatic zones in the Mediterranean region that offer
a potential for adaptation under a number of varied and
variable California environments has been confirmed.
Several principles, practices, and techniques have been
proven to be important for successfully displacing introduced annual Mediterranean plants of poor forage quality
with more desirable forage annual legumes. These factors
are plant exploration, plant introduction, evaluation of a
large number of collections, and matching the legume host
with an effective and competitive Rhizobium strain. Once
the array of adapted annual legume types is found, their
use will be optimized and sustained by providing them with
adequate levels of soil-deficient nutrients, such as phosphorus and sulfur for the California annual grasslands. Timely
and early-season animal grazing management will help to
reduce poor-quality annual spe~es, optimize seed production, and increase nitrogen ~cling. Where these legumes
can be used in pasture rotations with dryland cereal farming systems, one can use minimum tillage and selective
herbicides to enhance the annual legume component and
its regeneration.
Our results point out the need to maintain a testing and
evaluation program of present and future cultivar introductions to assess their adaptations to California conditions.
Through continued exploration for better adapted and persistent annual legume plant materials, the annual grasslands and associated vegetation types of California can be
restored and this natural resource sustained for multipleuse management needs.
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ACKNOWLEDGMENTS
We express appreciation to Gary Reece, the late Elgy
Kryger, Bob Eisele, and Bill Winans of the Watershed
Program, Department of Agriculture, San Diego County,
for their assistance in site preparation, encouragement,
and logistical support throughout the long evaluation program in San Diego County. A special thanks goes to Victor
Brown, UCCE County Director, whose encouragement and
belief in our potential during the developmental years was
invaluable. Others who provided valuable assistance were
Carol Adams, UCCE (UCR) for statistical analysis; Carlos
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