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November 10, 2005: Steve Groff is endlessly
curious about new ways to use cover crops to build up his
soil.
A current interest is how to make forage radishes work in
tandem with other cover crops. The main crops on his 175-acre
farm in Lancaster County, Pennsylvania, are soybeans, corn,
alfalfa and vegetables such as tomatoes and pumpkins. He experiments,
documents and invites the public to view what he has learned
in frequent field days at his Cedar Meadow Farm ().
Groff likes what the fall-planted radishes do to open up
soil and attract earthworms, but he needs something to provide
soil cover after April 1, when the winter-killed succulent
radish biomass has largely disappeared.
University of Maryland soil scientist Ray Weil is working
with Groff and others to find the cropping mixes that make
the best use of the soil-penetrating abilities of the radish
to break up soil compaction.
Planted in late summer through September in the Mid-Atlantic,
radishes exhibit aggressive rooting action in the fall, sending
a 1 to 2-inch diameter tap root down 12-18 inches. The plants
winter-kill by Christmas, much like fall-planted spring oats.
The roots rot by early spring, leaving holes in the field
much like an Aer-way® )
soil aeration tool would do. The fast-growing root crop is
of special interest to livestock farmers who spread manure
– or crop farmers after dry summers when there may be
excess fertility come fall – because the plants soak
up left-over N during the final months of the year.
Weil estimates that a good radish cover crop will capture
150 to 200 pounds of nitrogen per acre before winter killing.
The good/bad news is that this nitrogen will be available
by late March and early April, making it important to have
a heavy-feeding, early spring crop go in to use the nitrogen
before it leaves the soil via the water or air.
After Groff saw the relatively poor biomass cover left to
suppress early-season weeds in his first planting of radishes,
he added oats as a mixture with radishes in year two. The
radishes won that competition resulting in a meager stand
of oats to extend the spring soil cover.
In the fall of 2004 (year three of this experiment cycle),
he alternated the rows of the cereal and root crop to give
the oats a chance to grow. That worked well, and is his practice
again this fall (year four). Groff reports his other uses
of radishes: “Where I'm planting radishes into high-residue
situations, such as sweet corn stalks, I plant only radishes
as the corn stalks don't break down as quickly in the spring.
This fall I've planted radishes with hairy vetch/rye and with
crimson clover.”
Groff is adding the winter-annual legumes (vetch and clover)
for additional biomass to feed the soil and some residual
nitrogen (N) for the succeeding crop. His target pairings
at present are: radish/oats or radish/crimson cover before
sweet corn, and radish/rye-vetch before pumpkins.
He tried some later plantings this fall to test the planting
window. The results: “At this point, even with the warm
weather we've been having, I don't think planting past October
1 is worth it.”
“Radish ripper” idles steel
Groff is perfecting a technique he pioneered last year to
alleviate compaction in the farm driveways that provide in-season
access through his vegetable fields: “I put four, 7.5-inch
rows of radish over each wheel track and planted the middles
and edges with hairy vetch and rye. I call this my ‘radish
ripper,’” he says. “I tested the concept
last year and the radishes seemed to alleviate most of the
compacted driveways.
“I planted over 5 acres of driveways so far and the
ripper/stripper [implement] is still in the shed!”
Because of the number of visitors to his farm – and
his status as a Northeast region Sustainable Agriculture Research
and Education (SARE) farmer-educator – lots of farmers
want to try what they see on Groff’s farm. He’s
expediting radish experiments by harvesting his own seed and
making it available to other farmers and researchers, since
the seed is still difficult to get commercially in this country.
This year, he sold radish seed to about 20 farmers in five
states.
For others considering introducing the forage radish as a
cover crop, Groff notes:
- Radishes don’t like wet spots.
- Nematode suppression on following crops is alleged in
some quarters, but has not yet been documented in the fall-planted
cover-crop experiments he and Weil are involved in.
- Seeding rate is 12-14 lbs. per acre
- Planting window in the Mid-Atlantic is August 15 to September
20.
- Radishes are great at capturing Nitrogen left over in
fall from the previous years manure, compost and fertilizer
application, but…
- Radishes will be too stunted and yellow to do much if
there’s little nitrogen in the soil. For farmers with
biologically active soils this is not a problem, as the
organic sources keep releasing N in fall after main crops
have stopped taking it up.
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