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.