Can Radishes Be the Secret Weapon in Protecting Our Water From Big Farming's Runoff?

The crunchy crop—popular in salads and sushi—has proved remarkably effective at absorbing excess nutrients.

Daikon radish (Kiyoshi Ota/Reuters)

Oct 29, 2013· 2 MIN READ
Clare Leschin-Hoar's stories on seafood and food politics have appeared in Scientific American, Eating Well and elsewhere.

Beyond being pretty harbingers of spring, alternative medicine types love radishes for their digestive and immune benefits, and some even recommend slurping on a radish smoothie to detox your system. Sounds yummy. (Okay, not really.)

But there may be something to the notion that radishes reduce excess nutrients that contribute to dead zones and algae bloom—at least when it comes to storm water pollution and farm runoff.

To clarify, we’re not talking about pretty red salad radishes or white tipped breakfast radishes, says Ray R. Weil, a soil scientist at the University of Maryland, College Park.

“We’re talking about a daikon radish which is a major part of the diet in places like China and Japan,” he said.

From Maryland to Ohio to Iowa, farmers and scientists are taking a closer look at this vegetable’s ability to keep nutrients like calcium, phosphorus, nitrogen and sulfur in the soil where they’re valuable, and out of streams, rivers and bays where they become pollutants.

“We’re not growing them for food, but for the soil. It turns out they have a really strong root that can push through compacted soil that most plants can’t push through,” says Weil.

The radish roots can grow as big as an arm or leg, with smaller roots that delve seven feet or more and help keep topsoil in place, which prevents nitrogen from leeching into waterways. When winter arrives, the radish dies off leaving large holes on the soil’s surface which hold water in the field.

In Baltimore, Stuart S. Schwartz, a University of Maryland, Baltimore County researcher is planting radishes in vacant city lots for a project called “B’more Rad”. It's a sort of urban cover crop experiment to try to curb the polluted run-off that finds its way into the Chesapeake Bay, adding to the region’s troublesome dead zone.

Along the shores of Lake Erie—between Cleveland and Detroit—farmers who typically grow commodity crops like corn and soybeans, are planting radishes in the fall and are discovering that it’s reducing nutrient run-off into the Maumee and Sandusky rivers that feed into the Great Lake, and (Eureka!) the spicy cover crop is improving their soil too. Win-win!

In Iowa, cover crops, including radishes, are part of the state’s Nutrient Reduction Strategy to help keep farm run-off from entering the Mississippi River and eventually the Gulf of Mexico.

To top it all off, in a National Wildlife Federation report released earlier this month, researchers say cover crops, like radish, rye and clover, hold great promise when it comes to improving air quality, water quality and wildlife habitat, but little is known about how widely used they are by farmers.

“Unfortunately, we know very little about just how many acres are currently planted to cover crops. Since 2000, a handful of studies have attempted to calculate the acreage, but each of these have been regional in scope and use a range of different methodologies,” says the report.

The USDA says cover crops are rare, estimating that only 1 percent of all cropland acreage uses cover crops.

So why isn’t this relatively easy and seemingly successful fix being embraced by farmers and urban cities?

The NWF report points to barriers that include “disincentives in public policy, lack of regionally-specific information and limited availability of key technology and equipment.”

A fact sheet from Ohio State University also points out that sourcing good radish seed can be difficult as well.

Part of the reason may also simply be that a cover crop like radish does best if planted in August, when existing crops may still be in fields.

“It depends on the farmer and what they’re doing. Dairy farmers in Pennsylvania do have room to plant these. They have lots of manure to get rid of. They harvest corn to feed the cows before it’s dried to make silage. They harvest in August. Bingo!” says Weil.

And he adds, costs are minimal because no harvesting necessary and seed prices are reasonable.

“You don’t need much if you do a careful job of planting. It takes about 4 to 5 pounds per acre, and it costs about $3 a pound.”

While no scientist is saying a radish cover crop will cure all of big-farming’s ails, it does seem to be a promising step that we’d like to see more of America’s farmers embrace.