Project evaluates winter cover crops to build soil

Managers of the 163-year-old, family-owned Davis Ranch in Colusa County hope to build soil more resilient to the extremes of climate change by adding winter cover crops to its typical Sacramento Valley rotations of processing tomatoes, beans, wheat, sunflowers and corn.

Large winter areas of vetch and barley, and smaller plots of legumes, cereals and mustards, are also being studied closely for their ability to sequester more carbon in the ground at the ranch.

"We sampled the pH, EC, total nitrogen and carbon, and the soil organic matter before we started," said Sarah Light, University of California Cooperative Extension area agronomy advisor for the Sacramento Valley, who said a second soil sample was planned before the cover crop was planted again.

Light said baseline samples were taken at depths of 0 to 6, 6 to 12, 12 to 24 and 24 to 36 inches. She is supervising the two-year research and outreach project at Davis Ranch, in cooperation with the Colusa County Resource Conservation District and Richter Ag, as part of the California Department of Food and Agriculture Healthy Soils Program.

The program aims to help farmers both slow climate change by sequestering carbon in the ground and mitigate uncertainties by building soil that is more resilient under both drought and flood conditions.

"We're installing soil moisture sensors at 6, 12 and 24 inches, to see how the soil water is impacted by the various treatments," Light said.

Large plots within the 39-acre study area were planted in a vetch cover crop, a mixture of vetch and barley, or left fallow, while smaller plots were devoted to a variety of legume, cereal or mustard options.

The data from the study will not be collected and the numbers crunched until after the 2021 growing season, but Light said some promising early signs were readily visible.

"You could see the cover crop treatments did reduce weed pressure, compared to leaving the ground fallow," she said.

Another hopeful early visual sign, which had not yet been confirmed statistically, was that the corn grown in nitrogen-rich plots previously planted with the legume vetch cover crop looked better.

"Where we planted the straight vetch, the corn filled all the way up to the tip of the cob, compared to where we planted barley and corn. But that was just visual," said Anthony Chesini, farm manager for Richter Ag.

Richter Ag is a Colusa County rice farming operation that also engages in conservation-oriented management projects.

Colusa County RCD executive director Liz Harper is assisting in the field work and the outreach, which is an important part of the Davis Ranch project.

Light, who is also working on a cost study for winter cover crops in the Sacramento Valley, reported farmers say they pay between $28 and $50 an acre for the seeds, depending on the variety and seeding rate.

The wild card in the study is the range of costs for management of the cover crop, including termination and incorporation to ready the ground for the subsequent cash crop.

According to Light, a major obstacle for many Sacramento Valley farmers is the complexity of managing, terminating and incorporating the cover crop.

Though preliminary visual impressions suggest the impacts on the crop are beneficial, she said, the real payoff from keeping roots in the ground will be measured in long-term improvements to soil health.

"When you're building the soil, it may be all right at first if you're just not paying a yield penalty," Light said.

Though COVID-19 has made field meetings impossible, the researchers have presented their findings from the Davis Ranch project through virtual events.

Light and Harper expanded their outreach efforts by developing a YouTube channel, The Soil Health Connection, featuring discussions and interviews with soil science researchers and farmers.

In one interview, minimum-tillage researcher Jeffrey Mitchell, founder and director of the UC Conservation Ag Systems Innovation Center, discussed the many farmers who have become involved in looking for ways to make minimal tillage work in California.

"Many of our partners are private farmers," he told Harper and Light. "We have been working on ways to keep the soil covered and minimize soil disturbance."

In another interview, Soil Health Institute lead scientist Shannon Cappellazzi discussed progress toward developing standard soil-health measurements.

Fifth-generation Colusa County farmer Kim Gallagher discussed the help she received from neighbors when she came back to manage the family's 2,400-acre Erdman Farm after spending a decade as a high school science teacher.

"I'm lucky to have lots of farmers around me who share what they have been doing a long time," Gallagher said. "We started planting cover crops for pollinators for our almonds, and saw the benefits for the soil."

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)