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Bryan K. Sales, David R. Bryla, Kristin M. Trippe, Carolyn F. Scagel, Bernadine C. Strik, and Dan M. Sullivan

Biochar, as a soil amendment, has been reported to improve plant growth by increasing soil moisture and retaining nutrients. In a previous 12-week greenhouse study with highbush blueberry (Vaccinium hybrid), we found that amending soil with biochar alone or in combination with bokashi (fermented wheat bran) increased plant growth relative to unamended soil. The biochar was produced from mixed conifer species during conversion of wood to energy. In the current study, we aimed to validate the greenhouse findings under field conditions in western Oregon. The specific objectives of this 2-year study were to determine the effect of amending soil with biochar or a combination of biochar and bokashi on growth and early fruit production during establishment of northern highbush blueberry (Vaccinium corymbosum L.). To achieve these objectives, we transplanted ‘Duke’ blueberry plants into soil that was either unamended or amended with biochar or 4:1 (v/v) mixtures of biochar and bokashi or biochar and douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust. Each amendment was either applied in the planting hole or incorporated into the row. A treatment with douglas fir sawdust incorporated into the row was also included and represented the industry standard for the region. Plants grown in soil amended with biochar (in the planting hole or row) had 40% to 74% greater total dry weight at the end of the first growing season and 70% to 82% greater fruit yield in the second season than those grown with no amendments or in soil amended with sawdust. However, leaf Mg concentrations were lower with biochar, suggesting it could limit Mg uptake in blueberry. Soil amended with sawdust, on the other hand, was higher in organic matter, microbial activity, and wet stable aggregates than the other soil treatments but resulted in lower leaf N concentrations during the second year after planting. Unlike in the greenhouse study, biochar had no effect on root colonization by mycorrhizal fungi, and there was no benefit to using biochar with bokashi. Adding 4 L of biochar to the planting hole was considerably more economical than applying it to the row and cost $1320/ha less than the industry standard of incorporating sawdust in the row. These findings indicate that biochar is a promising soil amendment for commercial production of highbush blueberry.

Full access

Ryan C. Costello, Dan M. Sullivan, David R. Bryla, Bernadine C. Strik, and James S. Owen

New markets for organic northern highbush blueberry (Vaccinium corymbosum L.) have stimulated interest in using composts specifically tailored to the plant’s edaphic requirements. Because composts are typically neutral to alkaline in pH (pH 7 to 8), and blueberry requires acidic soil (pH 4.2 to 5.5), we investigated elemental sulfur (S0) addition as a methodology for reducing compost pH. The objectives were to 1) characterize initial compost chemistry, including the pH buffering capacity of compost (acidity required to reduce pH to 5.0), 2) measure changes in compost chemistry accompanying acidification, and 3) evaluate plant growth and mineral nutrition of blueberry in soil amended with an untreated or acidified compost. Ten composts prepared from diverse feedstocks were obtained from municipalities and farms. Addition of finely ground S0 reduced compost pH from 7.2 to 5.3, on average, after 70 d at 22 °C, and increased the solubility of nutrients, including K (from 22 to 36 mmol(+)/L), Ca (from 5 to 19 mmol(+)/L), Mg (from 5 to 20 mmol(+)/L), and Na (from 6 to 9 mmol(+)/L). Sulfate-S, a product of S0 oxidation, also increased from 5 to 45 mmol(−)/L. The composts were incorporated into soil at a high rate (30% v/v) in a greenhouse trial to evaluate their suitability for use in blueberry production. Shoot and root growth were strongly affected by compost chemical characteristics, including pH and electrical conductivity (EC). Potassium in compost was highly variable (2–32 g·kg−1). Concentration of K in the leaves increased positively in response to compost K, whereas shoot dry weight and root growth declined. Leaf Mg also declined in response to compost K, suggesting that elevated K concentrations in compost may cause Mg deficiency. Composts with the highest K were also high in total N, pH, and EC. Compost acidification to pH ≤ 6 improved growth and increased leaf Mg concentration. On the basis of these results, composts derived from animal manures or young plant tissues (e.g., green leaves) appear to be unsuitable for high-rate applications to blueberry because they usually require high amounts of S0 for acidification and are often high in EC and K, whereas those derived from woody materials, such as local yard debris, appear promising based on their C:N ratio, compost acidification requirement, and EC.

Open access

Bryan K. Sales, David R. Bryla, Kristin M. Trippe, Jerry E. Weiland, Carolyn F. Scagel, Bernadine C. Strik, and Dan M. Sullivan

Biochar, a carbon-rich, fine-grained residue obtained from pyrolysis of biomass, is known to improve soil conditions and to suppress infection by soilborne pathogens. However, its use as a soil amendment has received relatively little attention by the horticulture industry. Two 12-week experiments were conducted in a greenhouse to determine the potential of using biochar, produced from mixed conifers during conversion of wood to energy, as a soil amendment for highbush blueberry (Vaccinium hybrid ‘Legacy’). Plants in the first experiment were fertilized once a week with a complete fertilizer solution, whereas those the in the second experiment were fertilized once a month with a solution of ammonium sulfate. In both cases, the plants received the same amount of N in total and were grown in pots filled with unamended soil (sandy loam) or soil amended at rates of 10% or 20%, by volume, with biochar or a 4:1 mix of biochar and bokashi (biochar-bokashi). The bokashi was produced from fermented rice (Oryza sativa L.) bran and was added to increase nutrients in the amendment. Half of the plants in each soil treatment were inoculated with Phytophthora cinnamomi Rands, which causes root rot in blueberry. Although pH of the raw biochar was high (8.5), soil pH averaged 4.5 to 5.5 in each treatment. In the absence of P. cinnamomi, plants grown with 20% biochar or 10% or 20% biochar-bokashi had greater leaf area and 30% to 70% more total dry weight than those grown with 10% biochar or in unamended soil. Biochar also improved soil aggregation and increased root colonization by ericoid mycorrhizal fungi. The percentage of roots colonized by mycorrhizal fungi was 54% to 94% in plants grown with the amendments, but was ≤10% in those grown in unamended soil. Plants inoculated with P. cinnamomi were stunted and showed typical symptoms of root rot. Root infection by the pathogen was unaffected by biochar or biochar-bokashi and negated any growth benefits of the amendments. Overall, amending soil with biochar appears to be a promising means of promoting plant growth and mycorrhizal colonization in blueberry, but it may not suppress phytophthora root rot.