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A Molalla-area grower had experimented with other cover crops before finding successs with subterranean clover

Finding the right cover crop that works well with a particular agricultural crop is not always easy. What works for some growers and systems may not work for others.

However, a local hazelnut orchardist who has been experimenting with different cover crops has had success with subterranean clover.

Fred Kaser, a hazelnut producer in the Molalla area, has worked with the Clackamas Soil and Water Conservation District over the past few years to install a more efficient drip irrigation system that also allows him to apply fertilizer more precisely on his hazelnut orchards.

COURTESY PHOTO: LISA KILDERS - Molalla-area orchardist Fred Kaser has found that subterranean clover provides a good cover crop for his hazelnut orchard.

Once he was finished installing this practice, Fred became curious about what cover crops he might be able to use that would least interfere with his harvest but would reduce erosion and provide soil health benefits.

He experimented with different cover crops in his maturing orchards and in 2017 he tried subterranean clover in his northeast field. Subterranean clover is a cool-season annual legume that produces seeds during the summer at or below the soil surface (hence the name subterranean). Seeds then germinate in the fall after the first rains and grow rapidly through the fall/early winter.

It may go dormant for a time during the winter but becomes active again in early spring. It grows in densely matted clumps that are 6-15 inches tall and spreads through rootless runners reaching up to 3 feet in length.

After a few years of trial, Kaser noted that the "Subclover cover crop in what is now our nine-year-old hazelnut orchard is working very well and is quite easy to manage. Plus, now as the trees have sent roots out in the row centers, we are getting some nitrogen benefits. This orchard was visibly greener than our other orchards last spring. Every year it (the cover crop) gets better without having to add any seed since it is self-seeding.

COURTESY PHOTO: LISA KILDERS - Subterranean clover offers plenty of positives as a cover crop in a hazelnut orchard.

"This year we mowed it off in early April to about four inches high and then will let it bloom and go to seed. Then we will mow it off at ground level towards the end of June after the seed matures," Kaser added. "The clover residue is gone by hazelnut harvest and is not a problem. The last couple of years the clover has sprouted before hazelnut harvest and was maybe a half-inch high but did not cause any problems picking up nuts. We are broadcasting phosphorus and potassium in the fall and are putting all of the spring nitrogen on through the irrigation system plus the foliar feeds through early summer."

Kaser said the cover crop doesn't slow them down at harvest time like using a fine fescue grass would. This is because when they flail mow it in summer, the remaining residue is light, and turns to dust by late summer. Before harvest, the newly sprouted clover covers the orchard so there is less mud and dust at harvest time than if they had a bare floor.

There is one more benefit of the subterranean clover. It supports pollinators when the clover flowers in summer.

This system has worked so well for Kaser that he says if anyone is interested in using subterranean clover as a cover crop and would like to talk to him, he is happy to discuss the subject. Contact Scott Eden at Clackamas Soil and Water Conservation District at This email address is being protected from spambots. You need JavaScript enabled to view it. to get in touch with Kaser.

COURTESY PHOTO: LISA KILDERS - A look at Fred Kaser's northeast orchard where subterranean clover has proven to be a highly beneficial cover crop for hazelnuts.

Why are cover crops so important? Well, cover crops improve soil health, prevent erosion, reduce mud for vehicle traffic, smother weeds, improve water holding capacity, and increase biodiversity. Legumes, like subterranean clover, offer the additional benefit of providing nitrogen to the soil that can be taken up by the main cash crop.

On the other hand, not having a vegetative cover crop could mean soil erosion, reduced soil health, higher soil temperatures, and reduced soil moisture-holding capacity.

A new hazelnut orchard can use almost any cover including cash crops for the first few years, while the orchard is still immature. A perennial grass cover is another option during this time. Perennial grasses and most cash crops provide great soil health benefits, but once the orchard is fully mature there is little light on the orchard floor during the summer to support cover crops, reducing options.

Research on other cover crop options is ongoing with Nik Wiman at Oregon State University Cooperative Extension. Wiman has cover crop trials at the North Willamette Research and Extension Center in Aurora.


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