Benefits of using liquid sources of potassium fertilizer in northern highbush blueberry

Fertigation with N increases growth and production relative to granular N applications in northern highbush blueberry (Vaccinium corymbosum L.), but little information is available on whether there is any benefit to fertigating with other nutrients. The objective of this study was to evaluate the use of K for fertigation. An initial study was done in a greenhouse to identify appropriate combinations of liquid N and K sources for fertigation using potted plants of ‘Duke’ blueberry. The results indicated that the concentration of K in the soil solution increased by 25% with potassium sulfate (K2SO4) and by 39% with potassium thiosulfate (KTS) and, depending on the soil type, was highest when KTS was applied with urea or ammonium sulfate. Leaf K was affected by K as well as N fertilizers and, on average, was greater with than without K in both an optimum and high pH soil and with KTS than with K2SO4 in the latter soil. A second study was conducted to compare fertigation to granular application of K fertilizer using a mature planting of ‘Duke’ blueberry. Treatments included fertigation (once a week from April to August) with water-soluble K2SO4 or KTS, a single application (April) of granular K2SO4, and no K fertilizer. Each K fertilizer was applied at a total rate of 84 kg/ha K2O per year. After 2 years, the treatments have had no effect on yield or fruit quality. However, fertigation with K2SO4 or KTS resulted in lower pH and higher concentrations of K, Ca, Mg, and S in soil solution under the drip emitters than either no K or granular K2SO4, while granular K2SO4 resulted in higher concentration of K than any other treatment at 15 cm from the drip emitter (edge of the wetting front). The fertigated treatments also had greener leaves (based on SPAD meter readings), greater whole-plant leaf K concentrations, and nearly twice as much extractable K in the soil as the non-fertigated treatments. Additional measurements are underway to determine whether K fertigation will have any effect on yield or fruit quality over the long term

Comparative Effects of Nitrogen Fertigation and Granular Fertilizer Application on Growth and Availability of Soil Nitrogen during Establishment of Highbush Blueberry

A 2-year study was done to compare the effects of nitrogen (N) fertigation and granular fertilizer application on growth and availability of soil N during establishment of highbush blueberry (Vaccinium corymbosum L. “Bluecrop”). Treatments included four methods of N application (weekly fertigation, split fertigation, and two non-fertigated controls) and four levels of N fertilizer (0, 50, 100, and 150 kg·ha−1 N). Fertigation treatments were irrigated by drip and injected with a liquid urea solution; weekly fertigation was applied once a week from leaf emergence to 60 d prior to the end of the season while split fertigation was applied as a triple-split from April to June. Non-fertigated controls were fertilized with granular ammonium sulfate, also applied as a triple-split, and irrigated by drip or microsprinklers. Weekly fertigation produced the smallest plants among the four fertilizer application methods at 50 kg·ha−1 N during the first year after planting but the largest plants at 150 kg·ha−1 N in both the first and second year. The other application methods required less N to maximize growth but were less responsive than weekly fertigation to additional N fertilizer applications. In fact, 44–50% of the plants died when granular fertilizer was applied at 150 kg·ha−1 N. By comparison, none of the plants died with weekly fertigation. Plant death with granular fertilizer was associated with high ammonium ion concentrations (up to 650 mg·L−1) and electrical conductivity (>3 dS·m−1) in the soil solution. Early results indicate that fertigation may be less efficient (i.e., less plant growth per unit of N applied) at lower N rates than granular fertilizer application but is also safer (i.e., less plant death) and promotes more growth when high amounts of N fertilizer is applied

Applying Boron by Fertigation or as a Foliar Fertilizer Is More Effective than Soil Applications in Northern Highbush Blueberry

Boron (B) is often deficient in many fruit crops, including blueberry (Vaccinium sp.). The objective of the present study was to evaluate different methods for applying B fertilizers to two commercial cultivars of northern highbush blueberry (V. corymbosum Earliblue and Aurora) in western Oregon, USA. Treatments included soil application of sodium tetraborate in early April (before bloom), foliar application of boric acid in late April (during bloom or petal fall), weekly fertigation with boric acid from April through July, and a control with no B. The plants were irrigated by drip, and the fertilizers were applied for two consecutive seasons at a total rate of 1.5 kg·ha−1 B per year. Each method of fertilizer application increased the concentration of B in the soil solution relative to the control, but fertigation was the only treatment that increased extractable soil B to the recommended level of 0.5 to 1.0 mg·kg−1 B. In terms of plant nutrition, foliar application of B was the most effective method for increasing the concentration of B in the leaves, roots, and fruit, followed by fertigation. Soil application of B, on the other hand, was relatively ineffective and, after 2 years, only increased the concentration of B in the leaves of ‘Earliblue’. Although leaf B levels were initially deficient at the site (<30 ppm B), none of the B application methods had any effect on yield, berry weight, fruit firmness, or titratable acidity of the fruit in either cultivar. However, foliar applied B resulted in higher concentrations of soluble solids in the fruit than no B or soil applied B in ‘Earliblue’, whereas B fertigation resulted in higher concentrations of soluble solids than soil applied B in ‘Aurora’. On the basis of these results, applying B by fertigation or as a foliar spray is recommended over the use of soil applications of B fertilizer in northern highbush blueberry

Uptake and Partitioning of Nutrients in Blackberry and Raspberry and Evaluating Plant Nutrient Status for Accurate Assessment of Fertilizer Requirements

Raspberry and blackberry (Rubus sp.) plantings have a relatively low nutrient requirement compared with many other perennial fruit crops. Knowledge of annual accumulation of nutrients and periods of rapid uptake allows for better management of fertilization programs. Annual total nitrogen (N) accumulation in the aboveground plant ranged from 62 to 110 and 33 to 39 lb/acre in field-grown red raspberry (Rubus idaeus) and blackberry (Rubus ssp. rubus), respectively. Research on the fate of applied ¹⁵N (a naturally occurring istope of N) has shown that primocanes rely primarily on fertilizer N for growth, whereas floricane growth is highly dependent on stored N in the over-wintering primocanes, crown, and roots; from 30% to 40% of stored N was allocated to new growth. Plants receiving higher rates of N fertilizer took up more N, often leading to higher N concentrations in the tissues, including the fruit. Reallocation of N from senescing floricanes and primocane leaves to canes, crown, and roots has been documented. Accumulation of other macro- and micronutrients in plant parts usually preceded growth. Primocanes generally contained the highest concentration of most nutrients during the growing season, except calcium (Ca), copper (Cu), and zinc (Zn), which often were more concentrated in roots. Roots typically contained the highest concentration of all nutrients during winter dormancy. Nutrient partitioning varied considerably among elements due to different nutrient concentrations and requirements in each raspberry and blackberry plant part. This difference not only affected the proportion of each nutrient allocated to plant parts, but also the relative amount of each nutrient lost or removed during harvest, leaf senescence, and pruning. Macro- and micronutrient concentrations are similar for raspberry and blackberry fruit, resulting in a similar quantity of nutrient removed with each ton of fruit at harvest; however, yield may differ among cultivars and production systems. Nutrient removal in harvested red raspberry and blackberry fruit ranged from 11 to 18 lb/acre N, 10 to 19 lb/acre potassium (K), 2 to 4 lb/acre phosphorus (P), 1 to 2 lb/acre Ca, and 1 to 4 lb/acre magnesium (Mg). Pruning senescing floricanes in August led to greater plant nutrient losses than pruning in autumn. Primocane leaf nutrient status is often used in nutrient management programs. Leaf nutrient concentrations differ with primocane leaf sampling time and cultivar. In Oregon, the present recommended sampling time of late July to early August is acceptable for floricane-fruiting raspberry and blackberry types, and primocane-fruiting raspberry, but not for primocane-fruiting blackberry, where sampling leaves on primocane branches during the green fruit stage is recommended. Presently published leaf tissue standards appear to be too high for K in primocane-fruiting raspberry and blackberry, which is not surprising since the primocanes are producing fruit at the time of sampling and fruit contain a substantial amount of K.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Horticultural Science and can be found at: http://horttech.ashspublications.org/Keywords: leaf tissue analysis, nutrient removal, organic, Rubus, fertilization, nitroge

Nutrient Requirements, Leaf Tissue Standards, and New Options for Fertigation of Northern Highbush Blueberry

Northern highbush blueberry (Vaccinium corymbosum) is well adapted to acidic soils with low nutrient availability, but often requires regular applications of nitrogen (N) and other nutrients for profitable production. Typically, nutrients accumulate in the plant tissues following the same pattern as dry matter and are lost or removed by leaf senescence, pruning, fruit harvest, and root turnover. Leaf tissue testing is a useful tool for monitoring nutrient requirements in northern highbush blueberry, and standards for analysis have been updated for Oregon. Until recently, most commercial plantings of blueberry (Vaccinium sp.) were fertilized using granular fertilizers. However, many new fields are irrigated by drip and fertigated using liquid fertilizers. Suitable sources of liquid N fertilizer for blueberry include ammonium sulfate, ammonium thiosulfate, ammonium phosphate, urea, and urea sulfuric acid. Several growers are also applying humic acids to help improve root growth and are injecting sulfuric acid to reduce carbonates and bicarbonates in the irrigation water. Although only a single line of drip tubing is needed for adequate irrigation of northern highbush blueberry, two lines are often used to encourage a larger root system. The lines are often installed near the base of the plants initially and then repositioned 6–12 inches away once the root system develops. For better efficiency, N should be applied frequently by fertigation (e.g., weekly), beginning at budbreak, but discontinued at least 2 months before the end of the growing season. Applying N in late summer reduces flower bud development in northern highbush blueberry and may lead to late flushes of shoot growth vulnerable to freeze damage. The recommended N rates are higher for fertigation than for granular fertilizers during the first 2 years after planting but are similar to granular rates in the following years. More work is needed to develop fertigation programs for other nutrients and soil supplements in northern highbush blueberry.Keywords: fertilizer, humic acids, ammonium-nitrogen, soil pH, organic, Vaccinium corymbosu

Growth and Fruit Production of Highbush Blueberry Fertilized with Ammonium Sulfate and Urea Applied by Fertigation or as Granular Fertilizer

Fertigation with liquid sources of nitrogen (N) fertilizers, including ammonium sulfate and urea, were compared with granular applications of the fertilizers in northern highbush blueberry (Vaccinium corymbosum L. ‘Bluecrop’) during the first 5 years of fruit production (2008–12). The planting was established in Apr. 2006 at a field site located in western Oregon. The plants were grown on raised beds and mulched every 2 years with sawdust. Liquid fertilizers were injected through a drip system in equal weekly applications from mid-April to early August. Granular fertilizers were applied on each side of the plants, in three split applications from mid-April to mid-June, and washed into the soil using microsprinklers. Each fertilizer was applied at three N rates, which were increased each year as the plants matured (63 to 93, 133 to 187, and 200 to 280 kg·ha⁻¹ N) and compared with non-fertilized treatments (0 kg·ha⁻¹ N). Canopy cover, which was measured in 2008 only, and fresh pruning weight were greater with fertigation than with granular fertilizer and often increased with N rate when the plants were fertigated but decreased at the highest rate when granular fertilizer was applied. Yield also increased with N fertilizer and was 12% to 40% greater with fertigation than with granular fertilizer each year as well as 17% greater with ammonium sulfate than with urea in 2011. The response of berry weight to the treatments was variable but decreased with higher N rates during the first 3 years of fruit production. Leaf N concentration was greater with fertigation in 4 of 5 years and averaged 1.68% with fertigation and 1.61% with granular fertilizer. Leaf N was also often greater with ammonium sulfate than with urea and increased as more N was applied. Soil pH declined with increasing N rates and was lower with granular fertilizer than with fertigation during the first 3 years of fruit production and lower with ammonium sulfate than with urea in every year but 2010. Soil electrical conductivity (EC) was less than 1 dS·m⁻¹ in each treatment but was an average of two to three times greater with granular fertilizer than with fertigation and 1.4 to 1.8 times greater with ammonium sulfate than with urea. Overall, total yield averaged 32 to 63 t·ha⁻¹ in each treatment over the first 5 years of fruit production and was greatest when plants were fertigated with ammonium sulfate or urea at rates of at least 63 to 93 kg·ha⁻¹ N per year.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Horticultural Science and can be found at: http://hortsci.ashspublications.org/Keywords: Nitrogen management, Vaccinium corymbosum, Soil pH, Leaf nutrients, Fertilizer practices, Salinit

Weed Management Practices for Organic Production of Trailing Blackberry: I. Plant Growth and Early Fruit Production

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.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Horticultural Science and can be found at: http://hortsci.ashspublications.org/.Keywords: Yield, Drip irrigation, Fruit quality, Landscape fabric, Rubus, Weed mat, Leaf water potentialKeywords: Yield, Drip irrigation, Fruit quality, Landscape fabric, Rubus, Weed mat, Leaf water potentia

Weed Management Practices for Organic Production of Trailing Blackberry, II. Accumulation and Loss of Biomass and Nutrients

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.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Horticultural Science and can be found at: http://hortsci.ashspublications.org/.Keywords: Tissue nutrient status weed control, Organic fertilizer, Rubus, Landscape fabri

Weed Management, Training, and Irrigation Practices for Organic Production of Trailing Blackberry: III. Accumulation and Removal of Aboveground Biomass, Carbon, and Nutrients

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