CORVALLIS - Willamette Valley vegetable growers are experimenting with new ways to grow vegetables while protecting soil and water quality. Their methods combine new ideas of conservation tillage with old ideas of cover crops.
The process begins right after harvest in the fall. Instead of leaving the soil bare and vulnerable to erosion over the winter, these farmers will plant a crop of vetch or low-growing oats to keep their fields covered through the winter.
"Cover crops capture residual fertilizers in the fall, and keep chemicals from leaching into groundwater," explained Richard Dick, professor of soil science at Oregon State University. Cover crops add organic matter that creates air pockets in the soil for water to penetrate and be stored. Erosion is reduced, protecting both streams and soil.
Come spring, the fields will be prepared for planting. But instead of plowing the entire field to bury all of the crop residue, farmers will till only narrow eight-inch strips for seeding and leave the ground in between undisturbed.
Sam Sweeney, a Dayton-area vegetable producer, has seen marked improvement in soil conservation in the two years he has been using this "strip-till" method. Planting on a slope with conventional methods, Sweeney had previously lost soil, water, and nutrients into the creek.
"Strip tilling on that slope creates a barrier of undisturbed soil at each row. These small terraces catch water so it can soak into the soil and not drain off," he said.
Strip-tilling has many advantages, according to John Luna, of OSU's Integrated Farming Systems Program. It minimizes the disruption of desirable organisms such as earthworms in the soil that keep plants healthy. Cover crop residue can help smother weeds. And it limits the impact of tractors and other heavy equipment.
"Soil compaction limits the yield in many Oregon soils," Luna said. "Compacted soil prevents water from moving through the soil and restricts root growth. With conventional tilling methods, farmers traditionally make four to 10 passes through a field. With strip-tillage, growers make one or two passes over a field, and they are ready to plant."
With fewer passes, and more plant material in place, strip-tilling should improve soil structure so it will retain moisture and require less irrigation. Increased organic matter from cover crops can improve soil fertility and may reduce the need for chemical fertilizers.
Strip-till methods were used to plant more than 3,000 acres of vegetable crops in the Willamette Valley this year, yet Luna and others have some reservations.
"Strip-till isn't best for every situation," Luna said. "There are some situations where conventional tillage outperforms strip-tillage, and visa-versa. We don't understand the whole picture yet."
Sweeney concurs. "With all new practices, there is an awful lot to learn," he said.
Strip-till requires growers to invest in new equipment and monitor performance against conventional methods. Sweeney has seen economic savings in labor and fuel from reduced tillage. But speaking for the handful of pioneering vegetable growers in the Willamette Valley, Sweeney said, "Our main motivation is conservation."