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M. Gabriela Buamscha, James E. Altland, Dan M. Sullivan, Donald A. Horneck and John P.G. McQueen

The objective of this study was to determine if there are growth differences in geranium (Pelargonium ×hortorum ‘Maverick Red’) produced in fresh or aged douglas fir (Pseudotsuga menziesii) bark (DFB). A second objective was to document nitrogen (N) immobilization and decomposition rates of fresh and aged DFB to better understand the cause of growth differences. A series of experiments to measure plant response, N draw-down index (NDI), and percentage of cumulative carbon (C) loss were conducted on fresh and aged DFB. Geranium plugs were transplanted to containers filled with fresh or aged DFB. Treatments were arranged in a 2 × 3 factorial with two DFB ages (fresh and aged) and three N fertilizer rates (200, 300, and 400 mg·L−1). Plant growth was affected by DFB age in that geraniums were smaller when grown in fresh DFB. N draw-down analysis demonstrated that a large fraction of N in solution was immobilized in fresh and aged DFB. Carbon loss, measured as a gauge of bark decomposition, was not affected by N rate or bark type. Similarities in C loss between fresh and aged DFB agree with the similar N immobilization potential (NDI) in the two materials.

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M. Gabriela Buamscha, James E. Altland, Dan M. Sullivan, Donald A. Horneck and James Cassidy

A 1-year survey on the chemical and physical properties of Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] bark was conducted with the following objectives: 1) to document baseline chemical and physical properties of Douglas fir bark (DFB) that have relevance to production of container plants; 2) to determine the effect of DFB age on its chemical and physical properties; and 3) to document the consistency of those properties throughout the year. In June, August, October, and Dec. 2005, and February and May 2006, fresh and aged DFB samples were collected from two primary DFB suppliers (bark sources) for Oregon nurseries: source A offers a bark screened to 0.95 cm or less (fine) and source B screened to 2.2 cm or less (coarse). Samples were analyzed for pH, electrical conductivity (EC), essential plant macro- and micronutrients, bulk density, particle size distribution, and substrate moisture characteristic curves. Air space (AS), container capacity (CC), and solids were determined as a percent of container volume. Nonamended fresh and aged DFB contains appreciable extractable amounts of all measured plant macro- and micronutrients, except N. In general, the aging process reduced pH; and increased EC, and extractability of phosphorous, calcium, magnesium, boron, iron, and aluminum. Uniformity of DFB chemical properties throughout the year was affected by bark source and less so by age. In terms of physical properties, aged DFB had lower AS and higher CC compared with fresh DFB. Average differences in AS and CC between fresh and aged DFB within a source were 8% or less. Similar to chemical properties, uniformity of DFB physical properties was more affected by bark source than age.

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Handell Larco, Bernadine C. Strik, David R. Bryla and Dan M. Sullivan

A systems trial was established in Oct. 2006 to evaluate management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer each applied at rates of 29 and 57 kg·ha−1 nitrogen (N); sawdust mulch, compost topped with sawdust mulch (compost + sawdust), or weed mat; and two cultivars, Duke and Liberty. Each treatment was irrigated by drip and weeds were controlled as needed. The planting was certified organic in 2008. Bed type affected most leaf nutrients measured in one or both cultivars during the first year after planting, including N, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), boron (B), manganese (Mn), and zinc (Zn), but had less of an effect on leaf nutrients and no effect on soil pH, organic matter, or soil nutrients measured the next year. Feather meal contained 12 times more Ca and seven times more B than fish emulsion and resulted in higher levels of soil Ca and soil and leaf B in both cultivars, whereas fish emulsion contained three times more P, 100 times more K, and 60 times more copper (Cu) and resulted in higher levels of soil P, K, and Cu as well as a higher level of leaf P and K. Fish emulsion also reduced soil pH. Compost + sawdust mulch increased soil pH and organic matter and resulted in higher levels of soil nitrate-N (NO3-N), P, K, Ca, B, Cu, and Zn than sawdust alone and increased leaf K and B. Weed mat, in contrast, resulted in the lowest soil pH and increased soil ammonium-N (NH4-N). Weed mat also reduced soil Ca and Mg, but its effects on leaf nutrients were variable. Leaf Ca, Mg, and B were below levels recommended for blueberry the first year after planting when plants were fertilized with fish emulsion, whereas leaf N was low or deficient on average in the second year when plants were fertilized with feather meal. Leaf B was also low the second year in all treatments, and leaf Cu was marginally low. Leaf K, conversely, increased from the previous year and was becoming marginally high with fish emulsion. Fish emulsion, weed mat, and compost were generally the most favorable practices in terms of plant and soil nutrition. However, given the impact of each on soil pH and/or plant and soil K, further investigation is needed to determine whether these practices are sustainable over the long term for both conventional and organic production of highbush blueberry.

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Handell Larco, Bernadine C. Strik, David R. Bryla and Dan M. Sullivan

A systems trial was established in Oct. 2006 to evaluate management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer each applied at rates of 29 and 57 kg·ha−1 nitrogen (N); sawdust mulch, compost topped with sawdust mulch (compost + sawdust), or weed mat; and two cultivars, Duke and Liberty. Each treatment was irrigated by drip and weeds were controlled as needed. The planting was certified organic in 2008. After one growing season, allocation of biomass to the roots was greater when plants were grown on raised beds than on flat beds, mulched with organic mulch rather than a weed mat, and fertilized with the lower rate of N. Plants also allocated more biomass belowground when fertilized with feather meal than with fish emulsion. Although fish emulsion improved growth relative to feather meal in the establishment year, this was not the case the next year when feather meal was applied earlier. After two seasons, total plant dry weight (DW) was generally greater on raised beds than on flat beds, but the difference varied depending on fertilizer and the type of mulch used. Shoots and leaves accounted for 60% to 77% of total plant biomass, whereas roots accounted for 7% to 19% and fruit accounted for 4% to 18%. Plants produced 33% higher yield when grown on raised beds than on flat beds and had 36% higher yield with weed mat than with sawdust mulch. Yield was also higher when plants were fertilized with the low rate of fish emulsion than with any other fertilizer treatment in ‘Duke’ but was unaffected by fertilizer source or rate in ‘Liberty’. Although raised beds and sawdust or sawdust + compost produced the largest total plant DW, the greatest shoot growth and yield occurred when plants were mulched with weed mat or compost + sawdust on raised beds in both cultivars. The impact of these organic production practices on root development may affect the sustainability of these production systems over time, however, because plants with lower root-to-shoot ratios may be more sensitive to cultural or environmental stresses.

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John R. Yeo, Jerry E. Weiland, Dan M. Sullivan and David R. Bryla

Phytophthora cinnamomi Rands causes root rot of northern highbush blueberry (Vaccinium corymbosum L.), which decreases plant growth, yield, and profitability for growers. Fungicides are available to suppress the disease, but are prone to development of resistance in target pathogens and cannot be used in certified organic production systems. Alternative, nonchemical, cultural management strategies were evaluated to reduce phytophthora root rot in a field infested with P. cinnamomi. The field was planted with ‘Draper’ blueberry, which is highly susceptible to the pathogen. The soil was either amended with gypsum or not before planting, and the plants were irrigated using narrow (adjacent to plant crown) or widely spaced (20 cm on either side of the plant crown) drip lines and mulched with douglas fir sawdust or black, woven geotextile fabric (weed mat). A fungicide control treatment was also included in the study and consisted of applying two conventional fungicides, mefenoxam and fosetyl-Al, to plants irrigated with narrow drip lines and mulched with sawdust. Initially, root infection by P. cinnamomi was lower with the combination of gypsum, wide drip lines, and sawdust mulch than with any other treatment, except the fungicide control. The soil under weed mat accumulated more heat units than under sawdust and resulted in faster hyphal growth by the pathogen. However, plant growth was similar in both mulch types. The effects of drip line placement and gypsum, on the other hand, were interactive, and plants grown with a combination of wide drip lines and gypsum produced the greatest amount of biomass among the cultural treatments. Narrow drip lines negated the disease-suppressive effects of gypsum by moving zoospore-inhibiting Ca2+ away from the plant root zone, and also resulted in wetter soil near the crown of the plants, which likely promoted zoospore discharge and root infection. However, wide drip lines resulted in N deficiency symptoms during the first year after planting and, therefore, resulted in less plant growth than the fungicide control. Thus, if N is managed properly, this study suggests that concerted use of gypsum and wide drip lines can help suppress phytophthora root rot in northern highbush blueberry and increase production in field soils where the pathogen is present.

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Bernadine C. Strik, Amanda Vance, David R. Bryla and Dan M. Sullivan

A long-term trial was established in Oct. 2006 in western Oregon to identify organic production systems for maximum yield and quality in highbush blueberry (Vaccinium corymbosum L.). The planting was transitional during the first year after planting and was certified organic during fruit production (2008–16). Treatments included planting method (on raised beds or flat ground), fertilizer source (granular feather meal or fish solubles), and rate (“low” and “high” rates of 29 and 57 kg·ha−1 N during establishment, increased incrementally as the planting matured to 73 and 140 kg·ha−1 N, respectively), mulch [sawdust, yard debris compost topped with sawdust (compost + sawdust), or black, woven polyethylene groundcover (weed mat)], and cultivar (‘Duke’ and ‘Liberty’). Mulches were replenished, as needed, and weeds were controlled throughout the study. Raised beds resulted in greater yield than flat ground during the establishment years but had less effect on yield once the plants were mature. After 9 years, cumulative yield was 22% greater on raised beds than on flat ground in ‘Liberty’ but was unaffected by planting method in ‘Duke’. Cumulative yield was also 10% greater with feather meal than with fish solubles, on average, and 4% greater with the low rate than with the high rate of fertilizer. ‘Duke’ was particularly sensitive to fertilizer source and produced 35% less yield overall with fish solubles than with feather meal. By contrast, there was relatively little effect of fertilizer source or rate on yield in ‘Liberty’. In five of 9 years, yield was 8% to 20% greater with weed mat than with sawdust or compost + sawdust. Mulch type had no effect on cumulative yield of ‘Duke’, but cumulative yield of ‘Liberty’ was 11% greater with weed mat than with sawdust or compost + sawdust. Soil temperature was warmer under weed mat than under sawdust, and plants on raised beds covered with weed mat required more irrigation than those grown on flat ground mulched with sawdust. ‘Duke’ produced heavier, larger, and firmer berries with lower total soluble solids (TSS) than ‘Liberty’. However, other treatment effects on berry quality were relatively small and inconsistent. For example, berry weight was greater on raised beds than on flat ground, on average, but only by 3% (0.06 g/berry). Plants on raised beds also produced berries with slightly lower TSS than those on flat ground (15.2% and 15.7%, respectively, in ‘Liberty’, and 13.1% and 13.3%, respectively in ‘Duke’). There was no effect of fertilizer source or rate on TSS in ‘Liberty’ (15.5% on average), whereas in ‘Duke’, TSS was highest when fertilized at the high (13.7%) or low (13.4%) rate of fish, and was lower when using feather meal (12.9% and 13.1% for low and high rate, respectively). Plants fertilized with fish produced firmer fruit than with feather meal in five of the 7 years in which the measurements were taken. Also, fertilization with the higher rate of either product increased berry firmness compared with the low rate in six of the 7 years. The impact of mulch was inconsistent through the study period. On average, ‘Duke’ berries were softest when fertilized with the low (173 g·mm−1 deflection) and high (176 g·mm−1) rates of feather meal and were the firmest with the high rate of fish (182 g·mm−1). In ‘Liberty’, the low rate of feather meal produced softer fruit (157 g·mm−1) than the other fertilizer treatments (162 g·mm−1 on average). When this study was initiated in 2006, the most common organic production system in this region was raised beds with sawdust mulch and fertilizing with a high rate of fish solubles. For this production system, yield for mature plants in our study (2014−16) was the equivalent of 8.9−12.3 t·ha−1 in ‘Duke’ and 11.8−23.7 t·ha−1 in ‘Liberty’. However, when plants were grown on raised beds with weed mat and fertilized with the high rate of feather meal, yield increased to 10.2−19.3 t·ha−1, depending on year, in ‘Duke’. By contrast, there was little effect of production system on yield of mature ‘Liberty’ plants. These yields, particularly for the best-performing treatment combination in ‘Duke’, are similar to what are observed in commercial conventional fields or organic farms using similar management practices. Our results showed that choice of organic production system can have significant impact on yield and economic costs and returns.

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John R. Yeo, Jerry E. Weiland, Dan M. Sullivan and David R. Bryla

Phytophthora cinnamomi Rands is a ubiquitous soilborne pathogen associated with root rot in many woody perennial plant species, including highbush blueberry (Vaccinium corymbosum). To identify genotypes with resistance to the pathogen, cultivars and advanced selections of highbush blueberry were grown in a greenhouse and either inoculated or not with propagules of P. cinnamomi. Two experiments were conducted, including one with 10 commercially established cultivars and another with seven newly released cultivars, three commercially established cultivars, and three advanced selections of highbush blueberry. Pathogen resistance was based on the shoot and root dry biomass of the inoculated plants relative to the noninoculated plants within each genotype, as well as on the percentage of root infection among the genotypes. Resistant genotypes included four commercially established cultivars, Aurora, Legacy, Liberty, and Reka, and two new cultivars, Overtime and Clockwork. When these genotypes were inoculated, average relative shoot biomass was ≥60% of that of the noninoculated plants, whereas relative root biomass was ≥40%. ‘Star’, as well as two advanced selections (an early- and a late-season type) may also have some degree of resistance, but further investigation is needed. Relative shoot biomass of the susceptible genotypes, on the other hand, ranged from 19% to 53% and relative root biomass ranged from 11% to 26%. The susceptible genotypes included ‘Bluetta’, ‘Bluecrop’, ‘Bluegold’, ‘Blue Ribbon’, ‘Cargo’, ‘Draper’, ‘Duke’, ‘Elliott’, ‘Last Call’, ‘Top Shelf’, and ‘Ventura’. These cultivars are not recommended at sites with conditions conducive to root rot, such as those with clay soils and/or poor drainage.

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James W. Julian, Bernadine C. Strik, Handell O. Larco, David R. Bryla and Dan M. Sullivan

A systems trial was established to evaluate factorial management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer applied at 29 and 57 kg·ha−1 of nitrogen (N); sawdust mulch, compost topped with sawdust mulch (compost + sawdust), or weed mat; and two cultivars, Duke and Liberty. The planting was established in Oct. 2006 and was certified organic in 2008. Weeds were managed by hand-hoeing or pulling in sawdust and weed mat-mulched plots and a combination of hand-pulling, propane-flaming, and post-emergent, targeted applications of acetic acid or lemon grass oil to any weeds present in the compost + sawdust plots depending on year. Data were recorded on input costs and returns in Year 0 (establishment year) through Year 3. Plants were harvested beginning the second year after planting. Planting costs were $741/ha higher on raised beds than on the flat, but the higher costs were more than offset by an average of 63% greater yields that improved net returns by as much as $2861/ha. Cumulative net returns after 3 years were negative and ranged from –$32,967 to –$50,352/ha when grown on raised beds and from –$34,320 to –$52,848/ha when grown on flat beds, depending on cultivar, mulch, and fertilizer rate and source. The greatest yields were obtained in plants fertilized with the low rate of fish emulsion or the high rate of feather meal, but fertilizing with fish emulsion by hand cost (materials and labor) as much as $5066/ha more than feather meal. Higher costs of establishment and pruning for ‘Liberty’ compared with ‘Duke’ were offset by higher net returns in all treatment combinations, except feather meal fertilizer with either weed mat or compost + sawdust mulch. Mulch type affected establishment costs, weed presence, and weed management costs, which included product and labor costs for application of herbicides (acetic acid and lemon grass oil) as well as labor for hand-weeding as needed, depending on the treatment. The highest yielding treatment combinations (growing on raised beds mulched with compost + sawdust and fertilized with fish emulsion) improved cumulative net returns as much as $19,333/ha over 3 years.

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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.