Radishes. Delicious, tubular, and soil enhancing. In this case we’re talking about forage radishes also called daikon or tillage radishes (Raphanus sativus L), not the small red ones you carve into rosettes to garnish your iceberg wedge. They’re everything you want in a bb-sized seed package.
These radishes have a thick white taproot that can reach 8-16” with the finer portion extending another foot or more into the soil. They are effectively “bio-drilling” the soil. When the plants die, the roots decompose and leave vertical cracks in pan-like layers in the soil. The holes let water, air and roots of other plants enter the soil profile more easily.
After soil scientist Ray Weil saw them being used in Brazil as cover crops, he thought they might fit well in no-till corn and soybean production in the Mid-Atlantic United States. They proved to be a great fit. Planted in late summer after harvest, radish taproots break through compacted subsoils, and soak up 150 lbs of N/acre. When the roots decompose in the spring, they release nutrients. Corn, wheat, and soybean yields increased by 10+ bushels per acre when planted after radishes.
From Cropping Use to Pasture Use
In addition to bio-drilling through compacted soils and releasing nutrients, these roots build soil organic matter, attract beneficial soil organisms, and suppress weeds in crop fields. That makes them great for cropping between field crops. But how would they do on pasture? Four Vermont dairy farmers decided to try planting forage radish seed into mature pasture.
Timing was important to allow at least 7-8 weeks of growth for the pastures to reach maturity. In the northeast, the goal was to plant before the Fourth of July. Plant later than the Fourth of July, and soil moisture would be insufficient, and you start backing up against a potential killing frost in September. In warmer climates, planting dates could be later, depending on available moisture.
By planting right after a grazing event in early July, farmers were able to take advantage of the growth cycle of pasture plants, which then would need about 4-5 weeks to be ready for grazing again. Waiting too much later could mean hitting a dry spell or running out of time before the frosts came in.
In three of the four farms, emergence was a problem. Farmers put down about 10 lbs/acre, but on three of the farms, radishes didn’t show up except in a few scattered spots, and in bare spots such as around water troughs.
One farm was the exception. The farmer there grazed the paddocks prior to seeding, and then left heifers on the pastures for another day or so after seeding to trample in the seed. Grazing down hard and even having the herd on the paddock in the day or two after broadcast seeding helped seed-to-soil contact. Also, when he seeded in radishes, he put the 10 lbs/acre with 6 lbs of rye seed.
The radish stand in that pasture was vigorous, and well spread throughout the pasture.
The farmers noted the problems planting, chalking them up to thatch and lack of seed-to-soil contact. They observed that moisture was necessary for emergence, and continued moisture was necessary for the radishes to grow, so droughty periods soon after planting would kill off any radishes that had emerged.
Radishes as forage
For the farmer that had a successful stand of radishes, he really appreciated the addition of the radishes in his pasture. He let the pasture grow for more than 7 weeks after planting the radishes. The radishes provided high quality forage late into the fall, and the roots were enormous
The farmer noted that the radish leaves stayed green when the grasses were brown, retaining high forage quality later in the season. One year, he let the herd graze the radishes before the seven weeks were up, and the radishes weren’t always the herd’s first choice, grazing the radishes after grass. Another farmer who had a few clumps of radish grow said her cows pulled the radishes that emerged in her pasture and ate the roots like candy.
Overall, the farmer who got a good stand of radishes liked his experience. He observed that the pasture greened up stronger and brighter than its neighbors, which he attributed to the radishes planted in the previous year. He also saw a lot of worm castings.
At $3/lb, and spreadable by handspinner, broadcaster, or seed drill, all four farmers said they would keep the radishes in their toolbox, if only to tackle small compacted areas such as those around watering troughs. Interestingly, for the farmer with the great stand in the pasture, the radishes
that grew in the bare patch by the water trough were winter killed by the next spring. Grass planted with the radishes didn’t come back there the next year, perhaps shaded out by radishes’ vigorous growth.
If you try out forage radishes, let us know what you find. Now would be the time to plant.