What Is It? Forage Radish is a fast growing, frost-tender annual crop with long, thick taproots that penetrate deep into the subsoil.
Common Names: Fodder Radish, Forage Radish, Deep-Rooted Radish, Tillage Radish, Groundhog Radish, Deep-Rooted Daikon, Japanese Radish.
Latin Name: Raphaus sativus variety longipinnatus [radish edible v. long rooted]
Do Not Confuse With: Oilseed Radish = Raphaus sativus variety oleiferus. Oilseed radish has short, knobby roots unsuitable for deep tillage.
Terminology Note: Forage radish, cow horn turnip (Brassica rapa subspecies rapa), and stock beet = mangel wurzel (Beta vulgaris) are types of “tillage crops” grown to penetrate subsoils and break up hardpans = compacted soil layers. Modern farmers and agronomists often use the synonyms bio drills = bio-drills when speaking or writing about tillage crops.
Historical Note: Since the Middle Ages, farmers without draft animals have used daikon, cow horn turnip, and mangel wurzel as tillage crops to “plow” their fields.
Tap Root Dimensions: 10 to 24 inches long; 2 to 4 inches diameter.
Rooting Depth: 6 to 7 feet
Foliage Height: 1 to 2 feet
Growth Rate: Forage radish germinates and grows so rapidly that it overwhelms most weeds and companion crops. Most forage radish varieties grow 0.40 to 0.50 inches per day, depending on cultural conditions.
When To Plant: Forage radish is best planted in middle to late August as decreasing day length stimulates plants to form large tap roots. Spring planted forage radish has short, thin tap roots unsuitable for deep tillage.
Days To Maturity: 60 days (approximately) after seeding.
Yield: 10 tons = 20,000 pounds (dry weight) of biomass (taproots & foliage) per acre.
Planting Depth: 1/2 inch deep
Buying Seed: There are hundreds of varieties and land races of Daikon = Japanese Radish. Make certain to purchase only named varieties specifically selected for deep taproots. Do NOT buy VNS = Variety Not Stated seed as generic daikon is rarely suited for deep tillage.
Seeding Rate: 8 to 15 pounds per acre for non-irrigated fields; 6 pounds per acre for irrigated fields. Add 2 extra pounds per acre for broadcast seeding. Use 5 pounds per acre for mixtures.
Fertilizer: 300 pounds of 20-20-20 (20% nitrogen + 20% phosphorous + 20% potassium) per acre = 0.11 scale ounce per square foot. Alternatively, spread 3 to 6 tons = 6,000 to 12,000 pounds of cow manure per acre = 2.2 to 4.4 scale ounces per square foot.
How To Use Forage Radish: Forage radish winter-kills then rots quickly leaving clean fields of soft soil with many thousands of deep holes that trap water and sediment. Fields planted with forage radish have minimal water runoff or soil erosion.
Forage radish creates mellow, well aerated soil that is easy to plant. Crops following forage radish establish quickly and grow strongly.
Forage radish has an extensive root system that adds substantial amounts of organic matter to the subsoil. Decomposing radish tissue feeds millions of earthworms that help aerate and fertilize lower soil layers.
Forage radish has a deep root system which absorbs and holds nutrients that would otherwise leach away. Forage radish is an ideal cover crop for recycling excess nitrogen and other fertilizer elements that may contaminate surface and ground waters.
Living Mulch: Forage radish blots out most weeds but is sensitive to field traffic. Consequently, hand transplanting is recommended. Tall, fast-growing cash crops like tomato, pepper, and okra are best suited for growth among spring planted forage radish. Alternatively, transplant cash crops first then immediately top seed with forage radish or a mixture of forage radish and Dutch White Clover (Trifolium repens).
Field Trials: In a 4-year study on 4 farms in each of 4 counties, non-irrigated upland rice yields increased 14.9% on average following cover crops of forage radish. Yield increases were attributed to additional soil moisture (more rain soaks into soil planted with forage radish).
Farming Without Horses Or Tractors: Fence field and turn in hogs to dig up soil. (Do not put rings in hogs’ noses or they will not be able to root). Broadcast forage radish in middle to late August. Run sheep or other livestock over field to stomp seed into the ground. When hard frost kills radish plants, broadcast any kind of winter grain and low growing clover — or — wait until spring then frost seed spring grain and clover as early as practical.
Be A Good Neighbor: Decomposing forage radish has a sulfur-like smell similar to rotting onions or natural gas. The odor dissipates quickly but the brimstone smell can annoy homeowners if fields are planted too close to property lines.
Would You Like To Know More? Please contact the Author directly if you have any questions or need additional information about growing forage radish for soil improvement.
Eric Koperek = firstname.lastname@example.org
About The Author: Mr. Koperek is a plant breeder who farms in Pennsylvania during the summer and Florida during the winter. (Growing two generations each year greatly speeds development of new crop varieties).