Biochar for Blueberries: The Benefits of Soil Amendment

By: Octavia Hogaboam

location: USDA Horticultural Crop Research Unit and Oregon State University, Corvallis, OR

Blueberries are one of Oregon’s most valuable crops and are renowned not only for their great taste but also for their nutritional value. Blueberry growers, like all farmers, are constantly looking for ways to simultaneously increase yield, and improve the environmental and economic sustainability of production.  In other crops, biochar-based amendments have shown promise in accomplishing these goals, however, little is known about the response of blueberries to these novel amendments. 

Bryan Sales, as part of his PhD dissertation research, investigated the effects of biochar amendments on blueberry (Vaccinium sp.) growth and fruit production. To accomplish this, Bryan amended soil with biochar and analyzed changes in plant growth and fruit production.

Effects of Biochar on Blueberry Root Growth and Soil Characteristics

Blueberries grow best in well-drained, acidic soils with a high amount of organic matter. As such, it is standard to incorporate sawdust into the soil at the time of planting and periodically throughout the lifetime of the plant. Biochar usually has an alkaline pH (>7), which could potentially be detrimental to acid-loving blueberries, despite the improvement in other soil properties. However, 12 weeks after the soil was amended with 20% biochar, the soil

pH averaged 4.6-5.3. Unamended soil had only a slightly lower pH than the amended soil. This finding was important as significant changes in pH can stunt growth and reduce yields.

Biochar amendments improved root growth.  Bryan observed large increases in the density and biomass of roots in blueberries grown in biochar-amended soil (Figure 1) were observed [1]. Additionally, 10% and 20% biochar treatment led to an increase in the formation of soil aggregates that were not present in unamended soil. Soil aggregates are important for water retention, nutrient availability, and microbial activity. Likewise, the roots of plants grown in biochar also had 10-fold greater amounts of beneficial ericoid mycorrhizal fungi, which help the plant obtain nutrients from the soil.

Effects of Biochar Soil Amendment on Blueberry Leaf Development

Biochar amendments increased the size of the leaves as well. Again, among the different treatments, an amendment rate of 20% biochar led to the largest leaf area.

Bryan’s research showed that although biochar led to an increase in overall nutrition, it did not have a significant effect on the blueberry plant’s ability to fight off P. cinnamomi, a soil-borne pathogen that causes root rot. However, other studies have reported that biochar suppresses soil-borne pathogens at low concentrations, making this a subject matter to be studied further.

Effects of Biochar Soil Amendment on Blueberry Fruit Yield

This improvement in early fruit production is promising and applying biochar to the planting hole is considerably more economical than the addition of sawdust. Overall, plant growth and productivity have responded positively to biochar amended in soil. The results of Bryan’s research have shown that there should be renewed interest and attention to biochar as a soil amendment, even for acidophilic crops, like blueberries!

Bryan is currently an Assistant Professor at the University of North Carolina Pembroke, where he continues his research on sustainable solutions to agricultural and horticultural challenges.  

 

 

Further reading

[1] Sales B., Bryla D., Trippe K., Weiland J., Scagel C., Strik B., and Sullivan D. (2020). Amending Sandy Soil with Biochar Promotes Plant Growth and Root Colonization by Mycorrhizal Fungi in Highbush Blueberry. Hortscience 55(3): 353-361.

DOI: https://doi.org/10.21273/HORTSCI14542-19

[2] Sales B. (2019) Effects of Biochar and Nitrogen-Enriched Soil Amendments on Plant Growth, Mineral Nutrition, and Early Fruit Production in Highbush Blueberry (Vaccinium sp.) Oregon State University. Web: