In the case of the establishment trial, the soil was either
amended with two inches of yard waste compost or was left un-amended prior to seeding with 2 pounds per thousand
square feet of Yukon bermudagrass, or
alternatively, the same bermudagrass variety containing 5% by weight
microclover . In the case of microclover overseeding trial, one-quarter inch of
compost was applied as a topdressing immediately after seeding and once a year
thereafter. Plots not receiving compost topdressing treatment have received
urea at yearly rate of one pound of nitrogen per thousand square feet. The
establishment trial was initiated in July 2012 and the microclover overseeding trial
in September of 2012. The microclover seeding rate in the overseeding study was
two pounds of microclover seed per thousand square feet.
Jeff has been sending me regular updates on color, quality
and amount of clover present in each of the plots, however I did not grasp how
stark the difference in treatments have been until seeing the two trials this
past week. In brief, amending the soil with 2 inches of compost dramatically suppressed
the presence of clover in the bermudagrass at this site. As can be seen in the
first picture below there is very little
clover in a compost amendment plot that was seeded with the 95% bermudagrass,
5% microclover seed mixture. The amount of clover present in this plot is indistinguishable
from that of a nearby compost amended plot seeded with 100% bermudagrass at the
same time (lower picture).
Compost amended plot seeded with 95% bermudagrass, 5%
microclover seed mixture two years ago.
Compost amended plot seeded with 100% bermudagrass two years
ago.
It is likely that the enhanced availability of nutrients associated with the incorporation of compost (i.e., mostly nitrogen) favors bermudagrass growth and establishment over that of microclover. Dr. Derr also noticed that there was much less weed competition within the compost amended plots compared to the non-amended plots during establishment. The reduced level of weed competition in these plots may have also favored bermudagrass establishment over microclover establishment. Microclover and regular old white clover are present throughout the plots that were not amended with compost. This reinforces my belief that the lack of clover cover seen in the compost amended plots is primary due to the enhanced availability of nitrogen in these plots.
What stood out to me when viewing the overseeding trail
was that in plots overseeded with microclover but not topdressed with
compost, the presence of the microclover resulted in a darker colored turf than
in plots that were devoid of microclover. At this field station stop however Adam Nichols was quick to
point out that the primary difficulty with overseeding microclover into
bermudagrass is the inability in obtaining a homogenous mixture of the two
species. The appearance of the plots overseeded with microclover (with or
without the compost topdressing treatment) could best be described as “a patchy
mosaic” of microclover within the plot. If the approach of using microclover to
reduce lawn fertilizer use in bermudagrass is ever to gain favor, it appears
that obtaining something close to an homogenous stand of the two species will
require more than a onetime overseeding of microclover into bermudagrass.
Labeled plot in foreground was overseeded with
microclover 21 months earlier while labeled plot in background was not. The annual
amount of fertilizer applied to both plots is one pound of urea nitrogen per
thousand square feet.
