Adding forage radish to a summer-seeded annual forage mix could spice up fall grazing and boost soil health. That’s what years of research on the crop and recent forage trials indicate.
Depending on seeding rate, forage radish typically grows 12-18” tall with foot-long taproots, 1-4” in diameter, that can penetrate compacted soils, says Charlie White, Penn State University Extension associate.
A part of the brassica family, forage radish creates channels that remain after its taproots rot; each radish also has fine roots that create channels. In research White completed in compacted soils, forage radish grew two to three times more roots than crops such as rye and rapeseed.
“The holes left by the taproot help reduce runoff and erosion and significantly improve water infiltration for the following crop,” he says.
For late-season grazing, forage radish can work in the Upper Midwest with other annual forages such as turnips, sorghum-sudan, triticale, sunflowers and hairy vetch, says Kevin Sedivec, Extension rangeland specialist at North Dakota State University (NDSU).
But it should be no more than 15-20% of that forage mix and seeded at 0.75-2 lbs/acre, he says.
Sedivec and colleagues included forage radish as part of a “café treatment” in a three-year study of annual forages. They looked at forage production, soil health and the economics of different forage options. Last year, they also planted a small plot of forage radish by itself to get a better feel for its specific characteristics.
The crop is a powerhouse of phosphorus, calcium and protein, says Sedivec. It has three times the phosphorus of native range grasses.
“Our analysis shows the radish contains 3.75% calcium compared to 1% for millet and just 0.5% for native range grasses.”
The forage crop’s biggest weakness is its high water content: 82-85%, he says. Although that makes it very digestible – “our analysis showed that forage radish was 85-90% digestible, compared to 35-45% for native range grasses” – it would be impractical to graze alone. A fiber supplement would be needed to bulk up the diet.
The radish also breaks down throughout the winter, leaving little residue. “By spring there is nothing left in the field but holes,” Sedivec says.
It appears to be palatable to cattle, says animal scientist Brian Neville, now at the NDSU Central Grasslands Research Extension Center. He had worked with Sedivec on the forage-mix trials – seeded in July and grazed in mid-October after the first frost. But feeding too much radish to dairy cattle could flavor their milk, he warns.
Forage radish also is a popular cover crop, says White. “It works especially well after corn silage that has been harvested early.” The key is getting the crop planted at the right time: in August in Northern states and no later than Sept. 1.
“If the crop is planted early and gets a little moisture, within three weeks of plant emergence it will have grown a full canopy covering the soil. Its thick, dense foliage usually gets between 12 and 18” tall, and taproots reach their full size by November here in Pennsylvania.”
Forage radish is frost-tolerant to about 25°F, and it takes several below-20° nights to kill it. In North Dakota, that’s usually in late October or November. In Maryland, where White conducted much of his research, that would be in December or January.
A very competitive plant, it’s good at suppressing weeds, White says. “When it’s planted in a cover crop or forage mix, it can be very aggressive, so limit it to a seeding rate of about 2 lbs/acre.”
If grown as a cover crop on its own, plant the crop at 6-10 lbs/acre. “The higher the seeding rate, the smaller the radish tubers will be.”
Forage radish can be planted with taller crops such as sunn hemp or sorghum-sudangrass, which are able to grow above its tight canopy, says White.
The crop needs plenty of nitrogen (N) to put on fast growth, adds Sjoerd Duiker, Penn State soil scientist. “Planting it in a field with a good manure history is ideal.” If radishes are grown for forage and no manure has recently been applied, apply at least 50 lbs/acre of N preplant, he advises.
As a cover crop, it will take up 150-200 lbs residual N from the soil, adds White.
“Then it releases much of it again in the spring, after the crop has decomposed. But it does decompose quickly, so to take advantage of the early released nitrogen and prevent leaching beyond the root zone, you need to be able to plant something fairly early in the spring.”