Location: Horticultural Crops Research
Project Number: 2072-21000-055-011-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jul 1, 2020
End Date: Jun 30, 2022
The objective of the agreement is to determine the potential of using biochar as a cost-effective soil amendment for organic production of cultivated blueberries in the Pacific Northwest. The Pacific Northwest is extremely well suited for organic production of northern highbush blueberry (Vaccinium corymbosum). Currently, the region cultivates over 50,000 acres of blueberries and leads both national and worldwide production of the crop. Production occurs on both the east and west sides of the Cascade Range, which divides the region both geographically and climatologically. While most of the conventional production occurs west of the Cascades, more than 75% of the organic blueberry acreage is in the semi-arid east side, where the climate reduces the incidence of weeds, arthropod pests, and diseases. The region produced 32 million pounds of organic blueberries in 2019, which is as much as the rest of the United States combined. While the size of the organic blueberry industry has increased rapidly east of the Cascades, research is limited in the region. Consequently, many of the horticultural issues that are emerging remain unresolved. Native soils in this regions contain free lime and are high pH (> 7.8) and low organic matter content (< 0.7%). Therefore, to grow blueberries, growers are acidifying the soil and managing nutrition through trial and error to achieve suitable growing conditions. Growers report that building and maintaining soil organic matter is challenging in these soils and are concerned that low soil organic matter content could limit production and long-term viability in their fields. One possible way to increase organic matter is by adding biochar to soil. Biochar is a highly porous carbon-rich residue produced by thermal cracking (pyrolysis) of biomass under oxygen-controlled conditions. Chars produced by this process are recalcitrant and can persist in soils for years. They also tend to have high ion-exchange capacities and, when added to soil, increase retention of water and nutrients and improve porosity and aeration. Productivity has been shown to respond positively to biochar addition in a number of crops, especially in acidic and coarse-textured soils. Essentially, any form of biomass can be converted to biochar, including prunings from orchards and vineyards. Blueberry fields are pruned each winter. These prunings are mulched between the rows and away from the roots; therefore, any carbon and nutrients in them are no longer available to the plants. Biochar can be produced at both a small and large scale using blueberry prunings, including with mobile units that can be easily moved from site to site.
The study will be conducted in a 1-acre field of ‘Duke’ northern highbush blueberry located at the Hermiston Agricultural Research and Extension Center (HAREC) located in Hermiston, Oregon. The plants will be spaced 3 x 10 ft apart on rows raised beds covered with black weed mat. Treatments will be laid out in a randomized complete block design with five replicates and include wood chips (control) or biochar that is either spread on the soil surface in a 3-foot-wide band and incorporated prior to shaping the beds (method 1) or incorporated in a 6-inch-wide band during bed shaping (method 2). Biochar will be produced from local prunings of blueberry using a small-capacity air curtain burner. This type of unit is mobile and can be easily moved from site to site. Irrigation water will be acidified using a sulfur burner and applied using two lines of drip tubing per row. A dilution of fish emulsion will be injected through the drip system at a rate of 5 lb N/acre per week from April through July. Canopy development will be monitored remotely by capturing images of the field using a small unmanned aerial system (UAS) equipped with a multispectral camera. The images will be processed using camera software and converted to percent cover. Leaf samples will be collected in late-July each year as recommended for blueberry and analyzed for nitrogen and other nutrients using a combustion analyzer and inductively coupled spectrometry. Soil samples will be collected in September and analyzed for pH, EC, CEC, soil organic C content, and Mehlich 1 nutrients, as well as changes in soil structure, infiltration, and water holding capacity. Plants will be cropped during the second year after planting (industry standard). Ripe fruit will be harvested by hand from each plot and weighed on each harvest date (usually two or three per season) to determine the total yield. A subsample of berries will also be counted on each date to determine average berry weight and later analyzed for Brix and titratable acidity. Data will be analyzed using the generalized linear mixed model (GLIMMIX) procedure in SAS. Blocks will be treated as random effects with biochar treatment and application method as fixed effects. Data analysis will include a two-way ANOVA with a least-squares mean option; a Tukey–Kramer adjustment for multiple comparisons will be used for estimates and tests of significance (alpha = 0.05). Assumptions of normality and homogeneity of variances will be assessed utilizing the Shapiro-Wilk test (W > 0.80) and the Levene's test (alpha = 0.05), respectively. If no transformation satisfied the assumptions of normality and equality of variances, data will be non-parametrically analyzed using mixed models on rank transformed data.