Linneus, Linn County
* September 25, 2013
* October 1-3, 2013
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
This paper was published in the Proceedings 1996 AFGC
Annual Conference Vancouver BC, June 12-16, 1996.
SOIL FERTILITY AFFECTS ESTABLISHMENT AND PERSISTENCE
OF RED CLOVER IN GRAZED PASTURES
Interseeded legumes play an integral role in pasture
improvement programs in the humid-temperate region of the
US. Soil fertility may play a role in success of
establishing and maintaining legumes in grass dominant
swards. Impact of soil pH, P, and K on red clover
establishment and persistence in grazed pastures was
evaluated. Spring red clover (Trifolium pretense L.)
plant population and estimated canopy cover were not
significantly affected by soil fertility parameters.
Autumn measurements of red clover plant population were
highly correlated with both soil P and K levels. Mature
red clover plant numbers were most affected by soil P in
both the 0-3 in. and 3-6 in. layer. Both grass cover and
red clover population and canopy cover increased with
increasing levels of P. Soil pH had minimal effect on
any sward parameters, but the range of observed pH levels
was fairly narrow with minimum level of 5.8.
Introduction: Success of overseeding legumes in pastures
has been very variable. Soil fertility may be one factor
affecting establishment and subsequent persistence of
overseeded red clover. Numerous small plot studies have
addressed questions of legume response to soil pH,
phosphorus, and potassium levels, but less information is
available regarding plant response in grazed situations.
This study evaluated red clover population in the pasture
environment relative to estimates of several soil
Material and Methods: The study was conducted at the
University of Missouri-Forage Systems Research Center
located in north-central Missouri to evaluate the effect
of soil pH, Bray 1 P and exchangeable K on the
establishment and persistence of oversown red clover.
Eight pastures consisting of either smooth bromegrass
(Bromus inermis Leyss.) or orchardgrass (Dactylis
glomerata L.) sods were subdivided into three paddocks
for rotational grazing. One 5.33-acre paddock from each
base pasture was used in this study, providing four
replicates of each base grass sward.
Within each sample paddock, five transects were
established originating at the water source. Permanent
sampling sites, approximately 2 yd square, were
established along each transect at 100-ft intervals. Due
to variance in paddock shape, number of sample sites in
each paddock ranged from 26 to 33. At each sample site,
soil samples were collected from a one square-yard
quadrant each September for four consecutive years. A
different quadrant of the 2 yd square sample site was
used each year to avoid any effect the sample probe holes
may have had on water or nutrient movement to deeper soil
strata. Samples were taken to 6-in. depth and were
divided into the 0-3 in. layer and the 3-6 in. layer. At
the same time soil samples were collected, red clover
stand was assessed by two methods. Visual estimates of
ground cover percentage of red clover, base grass, and
bareground were made when the clover had regrown to
approximately 4 in. during the rest period. Individual
mature plants and red clover seedlings were also counted
within a 10.76 ft2 quadrat. The same two methods of red
clover stand evaluation were used in mid-April at all
Differences in red clover population among
individual paddocks and base grass swards were analyzed
using analysis of variance. Regression analysis was used
to determine relationships between soil fertility
measurements and red clover population. Both linear and
quadratic functions were evaluated. Where non-linear
response functions provided significantly better fit of
the data, second order equations are presented.
Results and Discussion: While individual paddocks
differed in mean soil fertility levels and red clover
population, smooth bromegrass and orchardgrass paddocks
did not differ in any of the measured parameters. Data
were pooled across all eight paddocks for regression
analysis of soil and sward characteristics. Significant
responses of sward parameters to soil variables are
indicated in Table 1.
Spring sward measurements were not highly correlated
with any soil parameters. Spring grass cover increased
slightly in response to higher exchangeable K levels in
the 3-6 in. layer but neither red clover plant population
or estimated ground cover was significantly affected by
any soil variable. Spring clover populations appear to
be more affected by severity of winter weather and
grazing pressure during the previous fall and winter
rather than by soil fertility.
Red clover seedling plants, mature plants and
estimated ground cover were all significantly affected by
soil variables at the September observation date. Clover
seedling number increased significantly as pH in the 0-3
in. layer increased above 6.0 indicating that the soil
environment for seedling establishment may be improved by
surface lime application. Observed bare ground
percentage decreased linearly with increasing pH in the
0-3 in. layer. The range of observed soil pH in this
study was only from approximately 5.6 to 6.8. This range
in pH may not have been great enough for a measurable
increase in red clover population due to increasing soil
Soil P had the greatest impact of the measured soil
variables on most sward parameters (Fig. 1 and 2). Both
grass cover and mature red clover plants measured in
September increased linearly as P in both the 0-3 and 3-6
in. layers increased. Estimated red clover ground cover
increased in response to higher P levels in the 3-6 in.
soil layer. All sward parameters increased at a more
rapid rate as 3-6 in. P increased compared to 0-3 in. P.
This response may be due to more extensive rooting at
deeper depths as 3-6 in. P increased. Two of the four
years of this study had below normal rainfall during the
July to September period. Deeper roots due to higher P
levels may have offset some drought stress. Baker (1980)
reported increased presence of volunteer red clover on
grass plots receiving P treatment compared to untreated
plots. He also indicated greater response of white
clover (T. repens L.) establishment to applied P compared
to lime on a limestone based soil while lime was the most
beneficial factor on a sandstone based soil.
Visual estimate of red clover canopy cover was not
highly correlated to soil fertility parameters. Number
of mature plants in the sward appears to be a better
indicator of pasture fertility status than does visual
estimate of canopy cover. The sward height at which
visual estimates were made may also have been too short
for red clover to have expressed the greater growth
potential that would have been expected on a higher
A surprising result was a highly significant
quadratic response of mature red clover plants to
increasing exchangeable K levels which indicated
declining plant numbers at higher levels of K. The
higher levels of K are far below any potential toxicity
level so the result was initially confusing. However, as
this data is sample site specific, the cause of this
response is easily explained. In this same grazing
study, soil nutrient redistribution by grazing livestock
has already been reported (Gerrish et al., 1993). Almost
all of the sample sites with K soil tests in excess of
400 lb/acre exchangeable K were within 150 ft of watering
sites. These sites also had the highest bare ground
estimates and lowest grass canopy cover estimates,
probably due to overgrazing and soil compaction in these
areas (Fig. 3). Thus while red clover plant population
initially increased in the general grazing areas as K
levels increased, the declining plant population at
higher fertility levels is in response to grazing
factors, not soil fertility. The red clover population
response to soil K described above is one of the reasons
why it is important to study forage fertility responses
in the pasture environment, not only in small plot
In summary, soil P appears to be a critical factor
in establishment and maintenance of red clover in grazed
pastures. Red clover plant population increased linearly
as soil P increased throughout the range of Bray P1
values measured in this study. Even though red clover
plant population increased at higher P levels, dry matter
yield has been shown to peak at much lower soil P levels.
Baker, Barton S. 1980. Yield, legume introduction, and
persistence in permanent pastures. Agron. J. 72:5:776-780.
Gerrish, J.R., J.R. Brown, and P.R. Peterson. 1993.
Impact of grazing cattle on distribution of soil
minerals. pp 66-72. IN: Proc. Amer. Forage Grassld.
Conf., March 29-31, 1993, Des Moines, IA. Amer. Forage
Grassld. Council, Georgetown TX.
Table 1. Levels of significance for regression coefficients with
soil parameters as independent variables.
Sward Parameter pH 0-3a pH 3-6 P 0-3 P 3-6 K 0-3 K 3-6
RC Cover, % .04 n.s. n.s. n.s. n.s. n.s.
RC mature plantsb n.s. n.s. n.s. n.s. n.s. n.s.
RC seedlingsb n.s. n.s. n.s. n.s. n.s. n.s.
Grass Cover, % n.s. n.s. n.s. n.s. n.s. .001
Bare Ground, % .02 n.s. n.s. n.s. n.s. n.s.
RC Cover, % n.s. n.s. .1 .01 n.s. n.s.
RC mature plants n.s. n.s. .001 .001 .001 .001
RC seedlings .001 n.s n.s. n.s. n.s. .03
Grass Cover, % n.s. n.s. .001 .001 n.s. .08
Bare Ground, % n.s. n.s. .001 .001 .05 .001
a soil depth, 0-3 in. or 3-6 in.
b plants per ft2
1Research Assistant Professor, University of Missouri-
Forage Systems Research Center, Linneus, MO 64653
Figure 1. Impact of soil P level on red clover plant
population in grazed pastures.
Figure 2. Impact of soil P level on percent bare ground and
grass canopy cover in grazed pastures.
Figure 3. Impact of soil exchangeable K on percent bare ground
and grass canopy cover in grazed pastures.
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