Rebuilding soil boosts threatened beet seed production

By Cathy McKenzie, WSU Mount Vernon

du-Toit-80MOUNT VERNON, Wash. – Growers in the fertile Skagit Valley have reported drops in historical beet seed yields of as much as 50 percent, according to Lindsey du Toit, vegetable seed pathologist at Washington State University. While disease and herbicides may cause isolated problems, researchers recently determined that poor soil is the prevailing factor.

“Our soils have a history of being very productive and rich in nutrients,” du Toit said. “But the longer and more you work the fields, the more the soils break down. So now they cannot hold moisture and nutrients as well as they did to produce high-yielding crops.”

Working together the past few years, western Washington seed producers, growers and researchers have found that irrigation, plant food, compost and cover crops dramatically increase the quantity and quality of the $2 million-per-year beet seed crop, du Toit said.

Early results are dramatic

Lindsey du Toit in a beet field. (Photo courtesy of John Evans)

“I just heard from one grower who said seed germination increased from 4 percent in last year’s crop to 95 percent for this year’s crop of the same variety of beet,” she said. “The main things he is doing differently include irrigating and foliar feeding based on the soil moisture stress and monthly foliar analysis data we provided.”

Another grower reported an increase in seed yield of 500 pounds per acre for a crop that was irrigated, foliar fed and grown in soil that had a rye cover crop for two years to help improve soil health. This was compared to the same variety grown in an adjacent field that had no cover crop.

“That’s huge,” said du Toit. “Such extreme results may not turn out to be indicative of the norm, but they are really encouraging.”

Collaborating to save valuable crop

Northwest Washington produces 95 percent of the U.S. beet seed crop. As yields declined, du Toit said, “some seed companies started taking beet seed production contracts overseas to obtain enough seed to meet the growing worldwide demand for beets.

“That has had an adverse economic impact on Skagit Valley farmers, who are paid based on the quality and quantity of seeds they produce,” she said.

The factors responsible for the drop in beet seed production came to light last winter, she said, when growers, seed company representatives and researchers met at the WSU Mount Vernon Research Center to share their observations – and a few frustrations.

“It helped that I was hearing such a diversity of stories and gaining empirical evidence about what was happening in the companies’ seed beds on Whidbey Island and in the farmers’ beet seed fields across the valley,” said du Toit.

Testing and assessing

Weed scientist Tim Miller. (Photo by Kim Binczewski, WSU Mount Vernon)

WSU Mount Vernon weed scientist Tim Miller conducted on-farm trials with herbicides while entomologists Lynell Tanigoshi and Bev Gerdeman examined beet seed crops for insect and mite pests.

During each month of the growing season, farmers brought in beet leaf samples for du Toit to send to a soil and plant testing lab, so any nutrient deficiencies could be detected and treated using foliar feeds.

To better understand soil moisture stress, WSU Skagit County Extension director Don McMoran set up a monitoring process in the spring. Twice-monthly soil moisture data were collected, allowing growers to see when fields were going into periods of moisture stress before the crops might show stress-related symptoms, such as wilting.

Entomologist Bev Gerdeman. (Photo courtesy of WSU Mount Vernon)

“This gives farmers the information they need to time irrigations to provide relief during the drier mid-June to September period, when crops are being pollinated and need energy for flowering and seed set,” du Toit said.

WSU Whatcom County regional extension specialist Chris Benedict recently began meeting with beet seed growers to assess cover crops and composts as economical means to supply soil nutrition and structure.

“As a result of collaborative trials … over the past few years, growers are considering long-term investment in composts and cover crops … that are cold-tolerant and can provide sufficient biomass as winter cover crops,” du Toit said.

Improving soil while making a profit

Looking ahead, du Toit and her colleagues are optimistic about the potential for reduced moisture and nutrient stress and increased crop production as a result of soil-building efforts throughout Skagit, Whatcom, Island and Snohomish counties.

“Farming in the (Skagit) Valley is going through a paradigm shift,” she said. “We need to look at ways to rebuild the soils which we have depleted over time.

“It’s exciting to see growers looking at irrigating, foliar feeding, adding compost and using cover crops,” she said.

“The challenge for us all moving forward is how to help work out agricultural systems that farmers can use to rebuild soils and still make a profit,” she said. “It’s not going to happen overnight. It will entail long-term investment in our soils.”


Lindsey du Toit, WSU Mount Vernon, 360-848-6141,

Don McMoran, WSU Skagit County Extension, 360-428-4270 x225,

Chris Benedict, WSU Whatcom County Extension, 360-676-6736 x21,

Tim Miller, WSU Mount Vernon, 360-848-6138,

Bev Gerdeman, WSU Mount Vernon, 360-848-6145,