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 (www.cedarmeadowfarm.com).
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
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
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® (www.aerway.com)
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
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
- Radishes are great at capturing Nitrogen left over in fall
from the previous years manure, compost and fertilizer application,
- 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.