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Oregon State University scientists have embarked on a major soil research project to identify soil management strategies in sweet cherry orchards that will improve overall fruit quality and tree health.

The three-year project, led by OSU’s Dr. Anita Azarenko, is funded by a $437,000 competitive grant of the U.S. Department of Agriculture’s Integrated Organic Program. Other project directors include nematologist Dr. Russell Ingham, soil scientist Dr. David Myrold, and Dr. Clark Seavert, agricultural economist, all from OSU. “It’s a huge project,” Azarenko said.

In replicated trials, the biological and economic effects of two organic fertility management systems during cherry orchard establishment and early production will be compared at the OSU Lewis Brown Research Farm in Corvallis, which is already certified organic, and at the Mid-Columbia Agricultural Research and Extension Center in Hood River. A cherry orchard at the Hood River experiment station is in the process of being certified organic.

In one of the fertility management systems, pelletized fertilizers made of fish and poultry products that provide nitrogen quickly but do not add significant organic matter are being used as well as geotextile landscape cloth for weed control.

The other system uses green manures, compost, and/or organic mulches. High-carbon compost and composted bark mulch will be applied to the plots after planting to control weeds and immobilize nitrogen in the fertile orchard soils.

Fruit quality

Nine grower cooperators—four organic and five conventional and alternative—are involved in the project. All of them are looking at different ways to enhance soil quality and improve fruit quality.

The project will look at faunal composition, functional specificity of soil microbes, and microbial activity.

“Nobody has ever done a complete study of soil biology in sweet cherries,” Azarenko said. “We want to find out that if we enhance soil biology, will we improve fruit quality? I know that I can probably affect soil biology (soil bacteria, fungi, nematodes, protozoa), but in doing so, does it really affect the overall fruit quality and tree performance?”

The bottom line, she said, is profitability. Does a healthier soil translate into improved fruit quality and yields?

The soil community is more than just chemical and physical properties of things like nitrogen, phosphorus, and good infiltration rates. She asks, “Is there a particular ratio for microbial population density that translates into a healthy soil?”

Soil biology research has been conducted on apples on the East Coast by researchers at Cornell University, New York. However, Azarenko is interested in the dynamics of a short-season crop like sweet cherries.

Studies at Cornell showed that high straw amendments to the soil increased tree damage from voles. “We haven’t seen that yet in any of the straw work done here,” she noted. “But that’s always a worry—when you change the environment, you can sometimes create other problems.”

And just because you change the soil biology population dynamics doesn’t necessarily mean that tree performance is increased.

Growers need to know things like how long the effects of compost last in the soil and about other soil-building strategies, Azarenko said. The grower trials will compare compost and straw amendments with a control or conventional practices.

Oregon State University researchers have studied laying down chopped straw in orchard rows as a way to conserve soil moisture in areas with low-volume wells or poor-quality water. But scientists are also finding value from the straw in building up soil carbon and organic matter and improving water infiltration and soil aeration.

At Azarenko’s own organic cherry orchard, she reported that she increased organic matter in the soil from 4 percent to 7 percent by using straw in the orchard rows.

She commented that the research is in part an outcome of all the different soil amendments being sold to improve soil biology and technology available to laboratories to perform a variety of soil biology assays for growers. As a scientist, she wants to know what is really needed to improve soil health.

“One of my goals is to reduce the number of inputs that growers need to provide to the orchard to achieve optimal production,” she said. “Fertilizer costs are going up as are biological soil amendments.

“I’m hoping if you use the right products at the front end, that in the long-term, we can design a soil program that works for us instead of requiring growers to keep putting things in the ground.”

The researchers are hoping to identify different soil community structure indicators that can be used to show successful use of soil management practices.

“My goal is to develop a matrix of desirable outcomes to serve as a guide for growers,” she said, explaining that by honing in on certain soil indicators, growers would know that their soil was within their acceptable range.

For example, if a lab analysis showed that the soil was at a certain carbon to nitrogen ratio, the grower would know that everything was in balance. Another indicator of the soil community structure may be the diversity of the nematodes.

By identifying the specific indicators, Azarenko believes that the costs for soil analysis can be minimized. “Instead of analyzing for 12 different things, hopefully we can reduce it down to one or two.”