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Evaluating tillage radishes

Dan Breen has planted tillage radishes in August as a cover crop for winter wheat over the last few years on his farm in Putnam, Ont., and sees many benefits in their use. Photo courtesy of Dan Breen.

Jan. 17, 2014 - A new option for a winter wheat cover crop is winning over farmers in Ontario.

“I’ve seen many immediate benefits, but I know I have yet to realize all the long-term benefits,” Dan Breen says of tillage radishes. “While they’re only one piece of the bigger puzzle of our overall crop production system and our soil management strategy, they are an integral part.”

Breen and his wife Kathy have a dairy operation in Putnam near London, Ont., and grow the usual field crop rotation of corn, beans and wheat, with occasional winter barley and alfalfa as well. The soil type of the farm is variable, with sandy soil in the fields along the Thames River, some clay loam and about 200 acres of heavy clay.

The Breens are coming up on 25 years of continuous no-till, and Dan says he has been experimenting with various cover crops for nine years, with tillage radishes for four of those. “The more I use cover crops, the more it makes sense,” he says. “The benefits of keeping the ground covered and actively growing are many, including nutrient retention, better soil health, weed suppression – the list goes on. The soil organisms need a green crop to work with, rather than just stover.”

Some of the benefits of tillage radishes are shared with many other cover crops, but some are distinctly their own. They control winter annual weeds and capture nitrogen in the fall to release it in the spring. When they decompose quickly after the winter, the radishes release a great number of nutrients (especially nitrogen) into the upper portion of the soil, which is then available to young winter wheat plants. Many studies have shown that they also increase corn and soybean yields afterwards.

“Because I’m no-till, I have to pay attention to things like water filtration and soil aeration,” Breen explains. “The tillage radishes, which I have seen grow to a depth of three feet, including the tap and hair roots and easily five inches across at the top, provide this. Some farmers use a deep tillage implement and I tell them with the radishes, I am doing that biologically.” Above ground, the radishes on Breen’s farm grow knee-high or more before the snow comes and will keep growing until it’s -10 C for three or four days in a row – sometimes that’s into January. “They’re photosynthesizing, capturing carbon and benefiting the soil,” Breen says. “In the spring, they hold the snow so it’s a more gradual melt.”

No-till farmers who want to reduce compaction and farmers who want to scavenge nitrogen are the two main groups interested in tillage radishes, says Dr. Rob Myers, regional co-ordinator and director of professional development (extension) programs at the University of Missouri. He notes that there is great interest in the U.S. in using radishes as a cover crop and that radish use (in field crops) has exploded over the last few years in many states, including Kentucky, Ohio, Idaho, Maryland, Minnesota and Missouri. They are also used in horticulture. “Farmers like them as they are relatively easy to seed,” Myers notes. “It’s a small, round seed that’s easy to broadcast.”

Breen uses the brand “Tillage Radish,” marketed by Pennsylvania-based Cover Crop Solutions and sold by Speare Seeds in Harriston, Ont., because it’s a well-established seed brand. To be effective cover crops, tillage radishes need time to grow before they’re killed by cold weather, so they don’t work well in a crop rotation after corn or soybeans. Breen says his radish planting date depends on the timing of wheat harvest and getting manure spread, and that could be anytime in August. “It depends on whether you spread straw and on the weather and so on, but if you can let volunteer wheat and some weeds come up and then do a Roundup burn-down and plant a bit later, you’ll get a better result,” he says. “It’s not necessarily a cheap crop – it’s an investment, and you want it to do well.” For planting in the first two years, Breen used a grain drill at seven pounds per acre. Last year as well as this year, in the hopes of more even emergence, he used a sugar beet disc in a unit planter at five pounds (125,000 seeds) per acre, and it worked well.   

Peter Johnson, provincial cereal specialist at the Ontario Ministry of Agriculture and Food, notes that radishes may plug drainage tile. Myers has not heard any reports of this, but admits the possibility. Jill Sackett, extension educator with University of Minnesota Extension, does not see this as a possible detracting factor. “Corn roots also can go down three to four feet [the depth at which tile lines are commonly placed], and the radishes decompose well in any case,” she notes. “When they do decompose quickly in the spring, it could be a problem in ground prone to erosion, so I recommend what I recommend with all cover crops – plant a mixture. Cover crops should not be a monoculture if you want to see multiple benefits.” Sackett adds that volunteer wheat can be suitable in functioning as the other cover crop in the mix but encourages mixtures of three or more species.

Myers adds that there can sometimes be an odour for a few days when the radishes decompose quickly in the spring, so you may want to plant them a little away from neighbours or chat with them about it.
 
Yield improvements?
While a recent U.S. Department of Agriculture funded survey showed corn and soybean yield improvements from cover crops as a whole, there’s less information specifically on radish impact on yield. “The decomposed radishes increase soil organic matter and eventually leave holes in the soil that allow water and air to enter and release nitrogen,” Myers says. “You would expect a yield benefit over the short term because of that, and over the long term after a few years, you would have a buildup of organic matter, which can support the achievement of higher yields as well.”

Breen has never done side-by-side corn, soybean or wheat comparisons, but in the corn he typically grows after radishes, he says he’s got more consistent emergence and more tilth to the soil with more consistent stands. “It’s due to the radishes rotting and providing better oxygenation and water filtration,” he says. “And I don’t think it’s useful to focus so much on immediate yield. We’re often short-sighted as farmers, and it’s not just about yield this year, but about improving soil quality and achieving excellent yield results over the long term. There is no doubt in my mind that radishes provide that.” Using the radishes also allows Breen to cut back on fertilizer. “I don’t want to quantify the amount because it’s going to be different for everyone, but it’s less, yes,” he says.

Although he hasn’t seen the long-term results and there is a lot left to explore with tillage radishes and other cover crops, Breen sees huge potential for all kinds of applications of radishes. “We did a three-acre test patch where we took off corn silage, planted radishes between the corn stalk rows of 15 inches, then in October, we planted wheat in between the radish rows,” he says. “The wheat looked fantastic early but struggled as the spring weather conditions progressed.”