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Renee H. Harkins, Bernadine C. Strik, and David R. Bryla

A study was conducted in western Oregon to assess the impact of cultivar and weed management strategy on accumulation and loss of plant biomass and nutrients during the first 3 years of establishment when using organic fertilizer. The study was conducted in trailing blackberry (Rubus L. subgenus Rubus Watson) planted in May 2010 and certified organic in May 2012. Treatments included two cultivars, Marion and Black Diamond, each with either no weed control after the first year after planting or with weeds managed by hand-weeding or the use of weed mat. Each treatment was amended with organically approved fertilizers at pre-plant and was drip-fertigated with fish emulsion each spring. Most primocane leaf nutrient concentrations were within the range recommended for blackberry. However, leaf nitrogen (N) was low in ‘Black Diamond’, especially when grown without weed control, whereas leaf boron (B) was low in all treatments. In many cases, leaf nutrient concentrations were affected by cultivar and weed management in both the primocanes and the floricanes. The concentration of several nutrients in the fruit differed between cultivars, including calcium (Ca), magnesium (Mg), sulfur (S), B, and zinc (Zn), but only fruit Ca was affected by weed management and only in ‘Marion’. In this case, fruit Ca was higher when the cultivar was grown with weed mat than with hand-weeding or no weeding. Total biomass production of primocanes increased from an average of 0.3 t·ha−1 dry weight (DW) during the first year after planting to 2.0 t·ha−1 DW the next year. Plants were first cropped the third year after planting and gained an additional 3.3 t·ha−1 DW in total aboveground biomass (primocanes, floricanes, and fruit) by the end of the third season. Fruit DW averaged 1.4 t·ha−1 in non-weeded plots, 1.9 t·ha−1 in hand-weeded plots, and 2.3 t·ha−1 in weed mat plots. Biomass of senesced floricanes (removed after harvest) averaged 3.2 t·ha−1 DW and was similar between cultivars and among the weed management treatments. ‘Marion’ primocanes accumulated a higher content of N, phosphorus (P), potassium (K), Mg, S, iron (Fe), B, copper (Cu), and aluminum (Al) than in ‘Black Diamond’. Weeds, however, reduced nutrient accumulation in the primocanes in both cultivars, and accumulation of nutrients was greater in the floricanes than in the previous year’s primocanes. Total nutrient content declined from June to August in the floricanes, primarily through fruit removal at harvest and senescence of the floricanes after harvest. Depending on the cultivar and weed management strategy, nutrient loss from the fruit and floricanes averaged 34 to 79 kg·ha−1 of N, 5 to 12 kg·ha−1 of P, 36 to 84 kg·ha−1 of K, 23 to 61 kg·ha−1 of Ca, 5 to 15 kg·ha−1 of Mg, 2 to 5 kg·ha−1 of S, 380 to 810 g·ha−1 of Fe, 70 to 300 g·ha−1 of B, 15 to 36 g·ha−1 of Cu, 610 to 1350 g·ha−1 of manganese (Mn), 10 to 260 g·ha−1 of Zn, and 410 to 950 g·ha−1 of Al. Overall, plants generally accumulated (and lost) the most biomass and nutrients with weed mat and the least with no weed control.

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Javier Fernandez-Salvador, Bernadine C. Strik, and David R. Bryla

The impact of organic fertilizer source on the growth, fruit quality, and yield of blackberry (Rubus L. subgenus Rubus Watson) cultivars (Marion and Black Diamond) grown in a machine-harvested, organic production system for the processed market was evaluated from 2011 to 2013. The planting was established in Spring 2010 using approved practices for organic production and was certified in 2012. Plants were irrigated using a dripline under a woven polyethylene groundcover (weed mat) installed for weed management. Two sources of liquid fertilizer were evaluated: 1) a corn steep liquor and fish waste digestion blend (“corn”; 2.5N–1.1P–1.2K); and 2) a fish solubles and molasses blend (“fish”; 4N–0P–1.7K). Fertilizers were applied by fertigation through the drip system at rates of 56 kg·ha−1 nitrogen (N) per year in 2011–12 and 90 kg·ha−1 N in 2013. The impact of fertigation on drip system performance was evaluated with two maintenance options, “flushing” and “no flushing” of the driplines. Total yield differed among years, whereas fruit soluble solids concentration and firmness as well as floricane biomass at pruning showed a year × cultivar interaction. ‘Black Diamond’ had greater total yield and average fruit weight than ‘Marion’, but produced a greater proportion unmarketable fruit. There was no effect of fertilizer source on yield, fruit quality, primocane length, or primocanes/plant in any year with the exception of fruit weight, which was greater with corn than with fish. ‘Marion’ had a greater floricane biomass when fertilized with fish than with corn. Soil nutrients were within the recommended range, except for boron (B), which was below recommended levels. Only soil nitrate-N was affected by fertilizer source, which was greater in ‘Marion’ than in ‘Black Diamond’ when fertilized with fish. Primocane leaf tissue nutrient concentrations were within recommended levels for all nutrients, except for calcium (Ca) and B, which were below recommended standards in both cultivars. Primocane leaf potassium (K) and zinc (Zn) concentrations were greater with fish than with corn. There was no fertilizer source or maintenance effect on emitter flow rate of the drip system in either year. However, flow rates decreased an average of 4.5% in the first year and 19% in the second year. Overall, there were no differences between the fertilizers on plant growth, yield, or fruit quality, and both fertilizers were suitable for planting establishment.

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Khalid F. Almutairi, David R. Bryla, and Bernadine C. Strik

Drought and mandatory water restrictions are limiting the availability of irrigation water in many important blueberry growing regions, such as Oregon, Washington, and California. New strategies are needed to maintain yield and fruit quality with less water. To address the issue, three potential options for reducing water use, including deficit irrigation, irrigation cutoffs, and crop thinning, were evaluated for 2 years in a mature planting of northern highbush blueberry (Vaccinium corymbosum L. ‘Elliott’). Treatments consisted of no thinning and 50% crop removal in combination with either full irrigation at 100% of estimated crop evapotranspiration (ETc), deficit irrigation at 50% ETc (applied for the entire growing season), or full irrigation with irrigation cutoff for 4–6 weeks during early (early- to late-green fruit) or late (fruit coloring to harvest) stages of fruit development. Stem water potential was similar with full and deficit irrigation but, regardless of crop thinning, declined by 0.5–0.6 MPa when irrigation was cutoff early and by >2.0 MPa when irrigation was cutoff late. In one or both years, the fruiting season was advanced with either deficit irrigation or late cutoff, whereas cutting off irrigation early delayed the season. Yield was unaffected by deficit irrigation in plants with a full crop load but was reduced by an average of 35% when irrigation was cutoff late each year. Cutting off irrigation early likewise reduced yield, but only in the 2nd year when the plants were not thinned; however, early cutoff also reduced fruit soluble solids and berry weight by 7% to 24% compared with full irrigation. Cutting off irrigation late produced the smallest and firmest fruit with the highest soluble solids and total acidity among the treatments, as well as the slowest rate of fruit loss in cold storage. Deficit irrigation had the least effect on fruit quality and, based on these results, appears to be the most viable option for maintaining yield with less water in northern highbush blueberry. Relative to full irrigation, the practice reduced water use by 2.5 ML·ha−1 per season.

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Carolyn F. Scagel, David R. Bryla, and Jungmin Lee

A study was conducted to evaluate the effects of salinity on growth and nutrient uptake in basil (Ocimum basilicum L. ‘Siam Queen’). Plants were fertilized with a complete nutrient solution and exposed to no, low, or moderate levels of salinity using NaCl or CaCl2. The plants in control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis (Blaszk., Wubet, Renker, & Buscot) C. Walker & A. Schler., to determine whether AMF mitigate the effects of salinity stress. Electrical conductivity (EC) of leachate collected from salinity treatments reached levels ≥8 dS·m−1 but had no effect on plant growth in the first 41 days of treatment. However, by 75 days, plants exposed to low and moderate levels of NaCl and CaCl2 had 20% to 38% less dry weight (DW) than controls. Reductions in DW were similar between NaCl and CaCl2 and was greater in roots than in shoots. Both NaCl and CaCl2 salinity reduced stomatal conductance (g S) within 25 days, but hastened flowering by 2–3 days, and nearly doubled the DW of flowers at 75 days. Salinity from NaCl increased uptake of Na and reduced uptake of Ca, whereas CaCl2 salinity increased uptake of Ca and reduced uptake of Mg and Mn. Both salts also increased relative uptake of N, Cu, and Zn, and reduced relative uptake of S and Fe. In general, Na was concentrated in roots and excluded from shoots, whereas Cl was concentrated primarily in leaves. Both salts reduced root colonization by AMF. However, AMF increased g S by 10% with NaCl and 22% with CaCl2, and increased shoot DW by 22% and 43%, respectively. Other than Ca and Cl, AMF did not enhance nutrient uptake under NaCl or CaCl2 salinity. ‘Siam Queen’ basil was moderately tolerant to salinity, due at least in part to exclusion of Na from the shoots, and inoculation with AMF increased tolerance to both NaCl and CaCl2 salinity. Differences in basil tolerance to NaCl and CaCl2 indicate plants may have different mechanisms for dealing with salinity and sensitivity is not solely a function of EC. This highlights the importance of understanding the source of salinity in irrigation waters and soil for predicting damage.

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Emily K. Dixon, Bernadine C. Strik, and David R. Bryla

Organic production of blackberries is increasing, but there is relatively little known about how production practices affect plant and soil nutrient status. The impact of cultivar (Black Diamond and Marion), weed management (nonweeded, hand-weeded, and weed mat), primocane training time (August and February), and irrigation (throughout the summer and none postharvest) on plant nutrient status and soil pH, organic matter, and nutrients was evaluated from Oct. 2012 to Dec. 2014 in a mature trailing blackberry (Rubus L. subgenus Rubus Watson) production system. The study site was certified organic and machine harvested for the processed market. The planting was irrigated by drip and fertigated with fish hydrolysate and fish emulsion fertilizer. Soil pH, organic matter content, and concentrations of soil nutrients, including ammonium-nitrogen (NH4-N), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), manganese (Mn), and zinc (Zn), were greater under weed mat than in hand-weeded plots. Soil K and boron (B) were below recommended standards during the study, despite a high content of K in the fish fertilizer and supplemental B applications. Primocane leaf nutrient concentrations were below the N, K, Ca, and Mg sufficiency standards in ‘Black Diamond’ and were lower than in ‘Marion’ for N, phosphorus (P), Ca, Mg, S, B, and Zn in at least one year. In contrast, floricane leaves and fruit tended to have higher nutrient concentrations in ‘Black Diamond’ than in ‘Marion’. Weed management strategy affected many nutrients in the soil, leaves, and fruit. Often, use of weed mat led to the highest concentrations. Withholding irrigation postharvest had limited effects on plant nutrient concentrations. Primocane training time affected the nutrients in each plant part differently depending on year.

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Emily K. Dixon, Bernadine C. Strik, and David R. Bryla

Relatively little is known about aboveground nutrient content of organic blackberry, and there is no published work on total carbon (C) content. Treatment effects on biomass, C, and nutrient content, accumulation, and removal were assessed over 2 years in a mature organic trailing blackberry (Rubus L. subgenus Rubus, Watson) production system that was machine harvested for the processed market. Treatments included two irrigation options (no irrigation after harvest and continuous summer irrigation), three weed management strategies (weed mat, hand-weeded, and nonweeded), and two primocane training times (August and February) in two cultivars (Black Diamond and Marion). Floricanes comprised an average of 45% of the total aboveground plant dry biomass, while primocanes and fruit comprised 30% and 25%, respectively. Depending on the treatment, the total aboveground dry biomass accumulation over the course of the season was 5.0–6.5 t·ha−1 per year, while C stock of the planting was an estimated 0.4–1.1 t·ha−1 in late winter. Carbon accounted for ≈50% of the dry biomass of each aboveground plant part, including primocanes, floricanes, and fruit. Weed management had the largest impact on plant biomass and nutrient content. No weed control reduced aboveground dry biomass, the content of nutrients in the primocanes, floricanes, and fruit, and the annual accumulation of dry biomass and nutrients, whereas use of weed mat resulted in the most dry biomass and nutrient content. Nutrient accumulation was similar between the cultivars, although February-trained ‘Marion’ plants had a greater removal of most nutrients in 2014 than the year prior. The amount of nitrogen (N) removed in the fruit was 22, 18, and 12 kg·ha−1 for weed mat, hand-weeded, and nonweeded plots, respectively, in 2013. In 2014, ‘Marion’ and ‘Black Diamond’ differed in N removed in harvested fruit when grown with weed mat at 18 and 24 kg·ha−1, respectively, whereas there was no cultivar effect when plants were grown in hand-weeded or nonweeded plots. Plots with weed mat tended to have the most nutrients removed through harvested fruit in both years. In 2014, N removal from August-trained ‘Marion’ was 5 kg·ha−1 N less than the other training time and cultivar combinations. Plants that were irrigated throughout the summer accumulated more dry biomass, N, potassium (K), magnesium (Mg), sulfur (S), boron (B), and copper in one or both years than those that received no irrigation after fruit harvest. The irrigation treatment had inconsistent effects on nutrient content of each individual plant part between the two years. Removal of nutrients was often higher than what was applied through fertilization, especially for N, K, and B, which would eventually lead to depletion of those nutrients in the planting.

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David R. Bryla, Thomas J. Trout, and James E. Ayars

Large, precision weighing lysimeters are expensive but invaluable tools for measuring crop evapotranspiration and developing crop coefficients. Crop coefficients are used by both growers and researchers to estimate crop water use and accurately schedule irrigations. Two lysimeters of this type were installed in 2002 in central California to determine daily rates of crop and potential (grass) evapotranspiration and develop crop coefficients for better irrigation management of vegetable crops. From 2002 to 2006, the crop lysimeter was planted with broccoli, iceberg lettuce, bell pepper, and garlic. Basal crop coefficients, K cb, defined as the ratio of crop to potential evapotranspiration when the soil surface is dry but transpiration in unlimited by soil water conditions, increased as a linear or quadratic function of the percentage of ground covered by vegetation. At midseason, when groundcover was greater than 70% to 90%, K cb was ≈1.0 in broccoli, 0.95 in lettuce, and 1.1 in pepper, and K cb of each remained the same until harvest. Garlic K cb, in comparison, increased to 1.0 by the time the crop reached 80% ground cover, but with only 7% of additional coverage, K cb continued to increase to 1.3, until irrigation was stopped to dry the crop for harvest. Three weeks after irrigation was cutoff, garlic K cb declined rapidly to a value of 0.16 by harvest. Yields of each crop equaled or exceeded commercial averages for California with much less water in some cases than typically applied. The new crop coefficients will facilitate irrigation scheduling in the crops and help to achieve full yield potential without overirrigation.

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Renee H. Harkins, Bernadine C. Strik, and David R. Bryla

Weed management practices were evaluated in a new field of trailing blackberry (Rubus L. subgenus Rubus Watson) established in western Oregon. The field was planted in May 2010 and certified organic in May 2012. Treatments included two cultivars, Marion and Black Diamond, grown in 1) non-weeded plots, where weeds were cut to the ground just before harvest; 2) hand-weeded plots, hoed two to three times per year; and 3) weed mat plots, covered with black landscape fabric. Each treatment was fertilized with fish emulsion and irrigated by drip. Weeds increased from 2010 through 2012 in both non-weeded and hand-weeded plots and required 38 and 90 h·ha−1 of labor to remove the weeds in the latter treatment in 2011 and 2012, respectively. Weeds in weed mat plots, in comparison, were confined primarily to the planting holes in the fabric and required only 1 h·ha−1 of labor for weed removal each year. Blackberry growth, in terms of number and dry weight of the primocanes, was similar among treatments during the first year after planting but differed with cultivar and weed management the next season. In 2011, ‘Black Diamond’ produced shorter but an average of three more primocanes per plant than ‘Marion’, whereas plants in hand-weeded and weed mat plots produced nearly twice as many primocanes as non-weeded plots. Hence, when fruit were produced on floricanes (the previous year’s primocanes) for the first time in 2012, ‘Black Diamond’ had 15% more yield than ‘Marion’, and weed control increased yield by 67% with hand-weeding and 100% with weed mat, on average. ‘Black Diamond’ and weed control also produced larger berries (measured as average individual fruit weight) with a greater water content but a lower soluble solids concentration. So far, of the three practices studied, weed mat was best suited to organic production of blackberries. The initial cost of the weed mat was far less than the cost of hand-weeding during the first 3 years after planting, and after only one season of fruit production, the yield benefit of weed mat provided enough profit to warrant its use over no weeding or hand-weeding.

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David R. Bryla, Jim L. Gartung, and Bernadine C. Strik

A study was conducted in a new field of northern highbush blueberry (Vaccinium corymbosum L. ‘Elliott’) to determine the effects of different irrigation methods on growth and water requirements of uncropped plants during the first 2 years after planting. The plants were grown on mulched, raised beds and irrigated by sprinklers, microsprays, or drip at a rate of 50%, 100%, and 150% of the estimated crop evapotranspiration (ETc) requirement. After 2 years, drip irrigation at 100% ETc produced the most growth among the irrigation methods with at least 42% less water than needed for maximum growth with microsprays and 56% less water than needed with sprinklers. Drip irrigation also maintained higher soil water content in the vicinity of the roots than the other methods but reduced growth when plants were over-irrigated at 150% ETc. Only 570 mm of irrigation water, or the equivalent of 1320 L per plant, was required over two seasons to reach maximum total plant dry weight with drip, whereas 980 mm or more water was needed with sprinklers and microsprays. Consequently, irrigation water use efficiency (defined as the difference in plant biomass produced under irrigated and rain-fed conditions divided by the total amount of irrigation water applied) was significantly higher with drip than with the other irrigation methods, averaging 0.41 g of total dry weight per liter of drip irrigation. In terms of both growth and water use, drip irrigation was the best and most efficient method to establish the plants.

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Fan-Hsuan Yang, David R. Bryla, and Bernadine C. Strik

Over-canopy sprinkler systems are used to cool northern highbush blueberry (Vaccinium corymbosum L.) fields and maintain fruit quality in the northwestern United States, but more information is needed to determine exactly when cooling is needed. The objective of this study was to identify the critical temperatures for heat damage to berries and for effective evaporative cooling. An initial study conducted in western Oregon in a mature planting of late-season ‘Elliott’ blueberry revealed that heat damage was typically observed within 1 to 3 days after an extreme heat event. Fruit damage, including softening, shriveling, and necrosis, occurred during both green and blue stages of development and was found primarily on sun-exposed berries, which on hot, sunny days (>35 °C) were 7 to 11 °C warmer than the ambient air temperature. A subsequent study was conducted to determine whether the critical temperature for heat damage differed between the green and blue fruit stages. In this case, ‘Aurora’ was compared with ‘Elliott’ blueberry. Berries were heated using a chamber-free convective unit and were exposed for up to 4 hours to berry temperatures of 42, 44, 46, and 48 °C. When the berries were green, significant damage was visible at each temperature within 1.5 to 2 hours in ‘Aurora’ and 3 to 3.5 hours in ‘Elliott’. Damage of green berries increased with time and temperature, and after 4 hours, ranged from 17% to 59% of the total berry number in the cluster in ‘Aurora’ and 10% to 24% in ‘Elliott’. Fruit damage at the blue stage was less than at the green stage and was only significant at 46 and 48 °C (within 3.5 to 2 hours, respectively) in ‘Aurora’ and at 48 °C (within 2 hours) in ‘Elliott’. Wax and cutin layers thickened on the berries as they progressed from green to blue, which perhaps increased their tolerance to heat at later stages of development. Based on these results, northern highbush blueberry fields should be cooled at air temperatures >32 °C during the green stages of fruit development and >35 °C during ripening.