Blueberry production is a major agricultural force in Oregon and Washington. Together, the two states account for roughly 55% of the United States’ cultivated blueberry production, with Washington producing about 29% of the U.S. total and Oregon about 26%.
East of the Cascade Range, organic blueberry production has strong potential because of favorable climate, yet serious soil challenges remain. Many sites there have sandy soils with low organic matter, and high pH — conditions that aren’t ideal for blueberries.
Growers often use organic amendments like sawdust to correct these issues, but the materials are often expensive and hard to get in the semi-arid environment. Oregon State University researchers aimed to find local, affordable alternatives that improve soil health for blueberries, especially in soils east of the Cascades.
A research team from Oregon State, Washington State University and the U.S. Department of Agriculture tested four locally available amendments in a new organic planting of ‘Draper’ blueberry at the OSU Hermiston Agricultural Research and Extension Center:
- Grape pomace compost
- Biochar
- Co-composted biochar and grape pomace
- Woodchips (the grower standard)
Amendments were either mixed into the soil or applied on the surface. Over two seasons, the team measured soil organic matter, nutrients and biological indicators such as microbial activity. They also profiled the soil’s bacteria and fungi.
Grape pomace compost — a waste product from the wine industry — delivered the biggest gains when incorporated into the soil. Compared with the woodchip standard and the other treatments, incorporated compost increased soil organic matter, boosted nitrogen, phosphorus and potassium, and raised microbial activity. Those changes support better nutrient cycling and water-holding capacity — key ingredients for blueberry growth in sandy soils.
Biochar and co-composted biochar offered some short-term benefits, such as helping manage nitrogen, but their effects were smaller in the first two years. Because biochar is stable and slow to break down, any larger benefits might emerge over a longer period. Across treatments, the overall makeup of soil bacteria and fungi did not shift much during the study window, which suggests that community-level changes may require more time.
For growers, these findings are practical and promising. Grape pomace is abundant in Oregon and Washington. Turning this byproduct into compost and using it in blueberry fields could help farmers reduce costs, recycle agricultural waste and improve soil health at the same time. While biochar may not deliver quick results, it could still play a role in long-term soil improvement and carbon storage.
The study also highlights how building healthy soils is a gradual process. While compost quickly improves nutrient availability and microbial activity, changes in the deeper microbial community structure may take years to emerge. Continued research will be needed to track how these amendments influence both soil and crop performance over the long run.
The results were published in Scientific Reports. Scott Lukas, who holds the Endowed Professorship for Northwest Berry Production and Management in the OSU College of Agricultural Sciences and OSU Extension Service, oversaw the study. Lead author Shikha Singh was a post-doctoral researcher in Lukas’ program and is now research assistant professor in the Department of Crop and Soil Sciences at Washington State University. Co-authors included Andrea Retano, Department of Horticulture, OSU; and David Bryla, USDA Agricultural Research Service.
The study was funded by the USDA National Institute of Food and Agriculture Organic Transitions Program (grant No. 2019-51106-30194), the USDA NIFA National Needs Graduate Fellowship Program (grant No. 2021-38420-34064), the OSU Agricultural Research Foundation (grant ID ARF#22082A) and the Washington Blueberry Commission.