WHITE CLOVER FOR WISCONSIN PASTURES?
Ken Albrecht, University of
Wisconsin-Madison
Derek Woodfield, AgResearch New Zealand
White clover has been described as the “key to the
international competitive advantage of New
Zealand’s pastoral industries”. World wide, it is recognized for its high
forage quality, ability to support high levels of intake by livestock, and
capacity to fix nitrogen. White clover is often thought of as the ideal pasture
plant because when animals graze it they consume only leaves and flowers. Growing points on the stolons (prostrate
stems) remain intact and are the sites of regrowth after grazing and in the
spring.
Professor Henry Ahlgren and his students studied
white clover in Wisconsin 50 years ago, but there has
been very little research on white clover in the northcentral states since
then. Much of the reason for the decline
in interest is that frigid winters and hot, dry periods during the summer are
responsible for unpredictable persistence and productivity of white clover in
this region. Because the original
taproot of white clover survives only 1 to 2 years (Brock and Albrecht,
unpublished research), the plant depends on stolon growth and survival to
maintain its presence in a pasture.
These horizontal stems lie on the soil surface and are subject to winter
extremes, trampling, and summer drought and heat. After the taproot dies, smaller roots
originating at nodes on the stolons must compete with grasses for moisture in
the upper six inches of soil. Thus, stolons begin to die back and productivity is diminished
during dry periods. Although natural
reseeding also occurs, long-term survival of stolons maximizes yield of white
clover.
Intentionally sown or volunteer, white clover in
some years can make up 20% or more of the forage production in many Wisconsin
pastures (Albrecht and Woodfield, unpublished observations). Unfortunately the naturalized white clover
that is so common in the state is usually not
productive, especially during dry or hot periods of the summer. We considered the question: are there
differences in performance between naturalized populations of white clover and
varieties currently available throughout the world? This was the incentive for us to test the
performance of a wide range of Wisconsin white clover
populations, white clover varieties and experimental lines.
In 1989, white clover ecotypes (naturalized
populations) were collected from 30 sites in southern Wisconsin. The chosen sites were all permanent pastures
with incomplete winter snow cover and variable grazing intensity ranging from
abandoned, ungrazed pastures to intensively grazed sheep pastures. In May 1995, populations of each of these
ecotype collections were transplanted into a pasture at the Lancaster
Agricultural Research Station in southwestern Wisconsin
along with four Ladino controls (California Ladino, Will, SRVR, and Tillman
II), two non-Ladino controls (Grasslands Huia and Grasslands Ranger) and 97
other varieties and experimental lines.
Each plot was 40 inches long and contained 10 plants transplanted into
an existing Kentucky bluegrass/orchardgrass mixed sward with five
replicates. Beef cattle were used to
rotationally graze the plots from April to October each year from 1995 to 1997. Data were collected several times during each
season to document growth characteristics and performance of each white clover
entry, but only representative data from a core of the entries in 1997 are
shown in Table 1 and discussed below.
Wisconsin ecotypes generally
had smaller leaf size and higher stolon densities but were less vigorous than
the traditionally grown Ladinos (Table 1).
Four medium-large leafed and one large leafed ecotype performed at least
as well as the California Ladino. These
ecotypes represent an important gene pool for future improvement of white
clover persistence under grazing in the northern USA. But most of the Wisconsin
ecotypes, although persistent, were not very productive as indicated by low
vigor scores. The data in Table 1 and
our observations, especially in mid- to late summer, demonstrate that the best
commercial varieties performed better than Wisconsin
ecotypes in this trial.
Of the control varieties, Tillman II, SRVR, Will,
and Grasslands Ranger have consistently performed better than California Ladino
and Huia, with Grasslands Ranger the best variety in the third year of this
trial (Table 1). Grasslands Ranger was
selected for persistence, stolon density and productivity after four years of
rotational grazing by sheep in New Zealand. Seed multiplication is in progress now and
limited amounts of seed will be available for on-farm testing in Wisconsin
in 2000 and commercial release is expected in 2001. Although white clover does not perform well
in droughty sites, our results suggest that newer, adapted varieties do deserve
another look in Wisconsin pastures with moderately to
poorly drained soils.
Table 1. Mean (and range) leaf size, stolon density,
flowering intensity and vigor of Wisconsin white
clover ecotypes and six control varieties during 1997.
Line Leaf size Stolon Flowering
Mean Vigor
(Huia=100) density (0 to 5) (Calif. Lad.=100)
(No. / ft2)
Wisconsin 107 169 3.3 80
ecotypes (83-145) (96-276) (2.4-4.8) (61-117)
Grasslands Huia
100 183 1.0
86
Grasslands Ranger
155 217 2.6 137
Will
152 173 3.8 110
California
Ladino 162 84 4.2 100
SRVR
159 139 4.2 121
Tillman II 170 158 4.4 120