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Residential development where stormwater is being monitored |
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Simulated home lawn plots |
Interpreting residential
development stormwater data is fraught with difficulties when the goal is to
evaluate the effectiveness of individual stormwater management practices. In
such settings the combined effects of topography, surface type (i.e. pervious
and impervious), building location, and the use of retention and conveyance
structures make it difficult to isolate the effectiveness of specific practices
in reducing flow during a storm event. Research
plots, on the other hand, offer the opportunity to evaluate the potential
effectiveness of individual, or a small subset of practices, on reducing
stormwater runoff.
In May of 2013 we began to measure
runoff losses from 2400 square foot plots consisting of either a well-fertilized
tall fescue lawn, or an unfertilized lawn comprised of tall fescue and microclover.
The latter lawn was creating using a tall fescue seed mixture containing 5% by
weight microclover at establishment. All lawns were established in the fall of
2012 on 3% hillside slope at the University of Maryland Paint Branch Turfgrass
Facility. Each lawn treatment was replicated twice. Prior to establishment, the soil in tall
fescue+microclover plots was amended with 2 inches of yard waste compost (i.e.,
Leafgro). All plots were rototilled to a depth of 5 inches (one pass) as part
of the seedbed preparation process. Five applications (April, June, Sept., Oct.
and Nov.) of 0.7 lbs nitrogen per thousand square feet were made to tall fescue
only lawns in 2013. The April application was made using urea. All other applications
were made using sulfur coated urea.
Monitoring of runoff was limited
to natural storm events with snowmelt events being excluded from data
collection due to equipment limitations. From 1, April to 31, December 2013
there were six storm events that generated runoff. An equipment malfunction
during one of the events preempted including this data the 2013 summary.
Cumulative runoff for the 5
storm events was 50% lower from the compost amended, non-fertilized tall fescue
+ microclover plots than from the well fertilized tall fescue plots that were
not amended with compost prior to turf establishment. On average, 3.1% of the precipitation
that occurred during the five storm events was lost as runoff from compost
amended, Tall fescue + microclover lawns, whereas, 6.2% of precipitation was
lost from the non-compost amended well-fertilized tall fescue lawn plots.
Increased shoot density is
often associated with a decline in runoff from lawns. Preliminary shoot data collected in 2013
suggest that a tall fescue + microclover lawn, when established in a recently
compost amended soil, does not need to
receive nitrogen fertilizer in the first year following establishment, in order
to maintain a shoot density that is
comparable (if not greater) than that present in a well fertilized tall fescue
lawn.
Shoot density data collected in 2013
Lawn Treatment
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Shoots (m2)
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July
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November
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Fertilized Tall fescue
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12,300
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11,200
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Tall fescue + Microclover in compost amended soil
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19,000
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20,600
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Pr > F
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0.16
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0.14
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Monitoring runoff from the
edge of isolated field plots does not consider the process of stormwater run-on into turf areas
from impervious surfaces such as rooftops, sidewalks and driveways that occur
in residential settings. As such, one should not interpret the results
presented here as indicating the use of compost as a soil amendment, and the
inclusion of microclover into a lawn seed mixture, will reduce residential
stormwater runoff by 50%. Actual reductions associated with the use of these
two practices will depend on many factors including, but not limited, to those
mentioned at the beginning of this blog. Nevertheless, the 2013 simulated home
lawn data do indicate that the practices of amending soil with large amounts of
compost, and including microclover as a component in the lawn seed mixture, will
promote lawn characteristics that reduce stormwater losses from lawn areas.
