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Denise Neilsen, Gerry Neilsen, Sunghee Guak and Tom Forge

Uncertain water supplies resulting from changing climatic conditions in western North America led to this investigation of the role of crop load reduction in maintaining performance of high-density ‘Ambrosia’ apple (Malus ×domestica) on M.9 rootstock. A split-plot experimental design was imposed for three growing seasons (2007–09) with six replicates of four main plot irrigation treatments and three crop load subplots comprised of three trees. Four season-long irrigation (Irr) treatments were applied through 2 × 4 L·h−1 drip emitters per tree and included Irr1) control [100% evapotranspiration (ET) replacement], Irr2) 50% ET replacement, Irr3) 50% ET replacement to half the emitters, and Irr4) an increasingly severe treatment commencing at 50% ET replacement (once every 2 days) in 2007 and progressing to 25% and 18% ET replacement, 2008–09. Three target crop loads were established annually, 4–5 weeks after bloom as low (2.5, 3, and 3.75), medium (4.5, 6, and 7.5), and high (9, 12, and 15) fruit/cm2 trunk cross-sectional area (TCSA) 2007–09, respectively, by hand thinning around 4 weeks after bloom. Volumetric soil moisture contents generally reflected the amount of water applied and ranged from 20% for control (Irr1) to <10% for Irr4. Both irrigation and crop load treatments affected midday stem water potential more than leaf photosynthesis and stomatal conductance (g S). By the 2nd and 3rd year stem potential values for irrigation treatments ranged from a maximum of −1.0 to −1.3 MPa for Irr1 to minimums ≤-2.0 MPa for Irr4. g S decreased as midday stem potential decreased, but at any given stem potential value was greater at high crop loads, presumably in response to an increased demand for photosynthates. Fruit size decreased as crop load increased, but as irrigation deficits became more severe, fruit size was more closely correlated with stem water potential than g S. Consequently, fruit size was controlled by two mechanisms, competition for photosynthates and the effects of plant water status on g S. Negative linear relationships between crop load and average fruit size were used to determine the crop load required to produce an average fruit size of 200 g at different irrigation deficits. It was not possible to achieve adequate fruit size when applications were very low, as at 18% to 25% ET in Irr4. Crop load reduction around mid-June had no negative consequences for fruit quality, enhancing fruit color, and soluble solids concentration (SSC) and did not affect the incidence of sunburn, internal breakdown or bitter pit at harvest.

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John Cline, Gerry Neilsen, Eugene Hogue, Shawn Kuchta and Denise Neilsen

Use of and interest in organic mulches for both integrated fruit production (IFP) and organic fruit production is increasing given recent efforts to reduce pesticide inputs and improve soil health. A series of four experiments was conducted in the southern interior of British Columbia over 5 years to investigate the use of a spray-on-mulch (SOM) slurry, comprised primarily of recycled waste newsprint fiber, as an effective method to control excessive weed competition and enhance tree establishment and performance. In four experiments, ‘Gala’, ‘Granny Smith’, ‘Ambrosia’, and ‘Honeycrisp’ apple (Malus ×domestica) trees on ‘Malling 9’ (‘M.9’) rootstock were exposed to a series of treatments including a glyphosate check, SOM waste paper, SOM over an organic underlay, SOM incorporated with dichlobenil or tackifier, SOM over black landscape fabric, rowcover cloth, or polyethylene plastic. SOM provided superior weed control in comparison with the glyphosate check treatment, a standard orchard practice in many modern orchards in North America. SOM application over compost, paper, and especially over cloth barriers were found to be more effective weed barriers than SOM alone. In comparison with glyphosate checks, SOM improved tree growth during tree establishment. Although the addition of dichlobenil provided season-long weed control, tree growth was diminished in comparison with SOM alone and remained similar to that of the glyphosate checks. There was little or no benefit of including a 2.5% tacking agent to help improve SOM integrity and long-term surface stability. When applied to bearing 4-year-old trees, SOM provided similar tree vigor as glyphosate checks over four growing seasons. The addition of landscape fabric, plastic, or cloth underlay material in combination with SOM improved tree vigor in formative years, but this benefit diminished over time. SOM-treated trees had greater cumulative yields over glyphosate checks after 3 years of production. SOM provided significant temperature moderation during the summer and winter months and provided moisture conservation during the summer. There were few SOM effects on plant nutrient status.

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Gerry Neilsen, Denise Neilsen, Shufu Dong, Peter Toivonen and Frank Peryea

Calcium application trials were undertaken in a 'Braeburn' apple (Malus ×domestica Borkh.) orchard with a history of bitter pit development at harvest. In 2000, an early season calcium chloride application strategy was compared with the unsprayed control and a late season application strategy. From 2001–03, the assessment of timing of calcium chloride sprays was extended by comparing effects of five weekly sprays applied during the growing season either early, middle, or late season. Other Ca application strategies tested included sprays of acidified calcium carbonate suspensions and soil application of calcium thiosulphate. In the first experiment, early application of calcium chloride reduced the occurrence of bitter pit at harvest and after 3 months cold air storage, despite having low harvest fruit Ca concentrations. Late sprayed fruit had a higher incidence of bitter pit. In the second experiment, the later calcium chloride was sprayed in the growing season, the higher the fruit Ca concentration at harvest. Despite this, no bitter pit was measured at harvest for 2 years for early and midseason calcium chloride spray regimes. In 2003, when Ca disorders were severe and fruit large, bitter pit was observed despite early season calcium chloride sprays. Soil calcium thiosulphate application and foliar sprays of acidified calcium carbonate suspensions failed to meaningfully augment harvest fruit Ca concentrations and affect bitter pit incidence.

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Eugene J. Hogue, John A. Cline, Gerry Neilsen and Denise Neilsen

Fertigated ‘Gala’ apple trees on M.9 (Malus domestica Borkh.) rootstock, planted in 1998, were grown on a coarse soil for 6 years (1998 to 2003) and exposed to eight orchard floor vegetation management treatments within the tree row. These consisted of a glyphosate control; three waste paper mulch treatments [spray-on mulch paper mulch (SM), SM incorporated with dichlobenil, SM applied over uniformly spread shredded office paper (SOP)]; and four living cover crop mulch treatments [dwarf white clover (WC), sweet clover (SC), hairy vetch (HV), and annual rye]. There were no significant treatment effects on leaf nitrogen (N) and phosphorus (P) status; however, leaf potassium (K) levels were negatively affected by the living mulch treatments in 2 of 5 years. Tree vigor was diminished by several of the orchard floor vegetation management systems in 5 of 6 years. Trees receiving an SM treatment grew more rapidly than trees receiving the ground cover treatments and trees receiving a glyphosate treatment had relatively poor but comparable growth to several of the cover crop treatments. Growth response in trees receiving SM were observed in all production years. After 6 years, cumulative yields were highest from trees receiving any of the three SM or glyphosate treatments and significantly less for any of the ground cover treatments. Weed growth within the rye cover crop was significantly reduced in comparison with the other living mulches; however, it remained sufficiently competitive to contribute to diminished overall yield and tree growth in comparison with the SM and gylphosate control treatments. Overall, response of leaf K concentration to mulch treatments was insufficient to prevent low K levels after 5 years. The addition of K through the organic mulches or recycling of K by cover crops was insufficient to avoid the development of low leaf K levels. Annual fertigation of K, in addition to N and P, appears necessary to maintain adequate vigor and yield when using mulches or cover crops in intensive, drip-irrigated apple orchards grown on coarse soils.

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Gerry H. Neilsen, Denise Neilsen, Frank Kappel and T. Forge

‘Cristalina’ and ‘Skeena’ sweet cherry cultivars (Prunus avium L.) on Gisela 6 (Prunus cerasus × Prunus canescens) rootstock planted in 2005 were maintained since 2006 in a randomly blocked split-split plot experimental design with six blocks of two irrigation frequency main plot treatments within which two cultivar subplots and three soil management sub-subplots were randomly applied. The focus of this study was the growth, yield, and fruit quality response of sweet cherry to water and soil management over three successive fruiting seasons, 2009–11, in a cold climate production area. The final 2 years of the study period were characterized by cool, wet springs resulting in low yield and yield efficiency across all treatments. Soil moisture content (0- to 20-cm depth) during the growing season was often higher in soils that received high-frequency irrigation (HFI) compared with low-frequency irrigation (LFI). HFI and LFI received the same amount of water, but water was applied four times daily in the HFI treatment but every other day in the LFI treatment. Consequently, larger trunk cross-sectional area (TCSA) and higher yield were found on HFI compared with LFI trees. Soil management strategies involving annual bloom time phosphorus (P) fertigation and wood waste mulching did not affect tree vigor and yield. Increased soluble solids concentration (SSC) occurred with LFI. Decreased SSC occurred with delayed harvest maturity in trees receiving P fertigation at bloom. The largest fruit size was correlated for both cultivars with low crop loads ranging from 100 to 200 g fruit/cm2 TCSA. Overall cool, wet spring weather strongly affected annual yield and fruit quality, often overriding cultivar and soil and water management effects.

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Tom Forge, Gerry Neilsen, Denise Neilsen, Eugene Hogue and Dana Faubion

A variety of organic mulches and amendments have been observed to improve soil quality and productivity of apple orchards. Alfalfa hay and composted dairy manure solids (CDS) are readily available in the apple-growing region of the Pacific Northwest and British Columbia and could be used to improve orchard performance. The objective of this research was to determine the influences of CDS amendment and alfalfa hay mulch on populations of soil microfauna, soil chemical properties, and early growth; nutrient uptake; and yield of apple planted into a fumigated coarse-textured soil in central Washington State. Alfalfa mulch significantly improved tree vigor and fruit yield with minimal adverse effects on fruit quality, whereas the CDS amendment had minor effects on vigor and yield. Both alfalfa mulch and CDS amendment increased availability and uptake into leaves and fruit of most key nutrients but plant nutrient concentrations were not deficient in control plots, suggesting that increased nutrient availability was probably not the primary reason for the increased vigor attributed to alfalfa mulch at this site. The alfalfa mulch resulted in elevated populations of microbivorous nematodes and protozoa that persisted through later years of the experiment, indicating greater overall microbial activity, mineralization of nutrients, and possible direct stimulation of root growth under mulch; the CDS amendment did not consistently enhance populations of microbivorous nematodes. The alfalfa mulch, but not CDS amendment, suppressed the buildup of populations of root-lesion nematodes, which are important components of the replant disease complex that was suppressing tree growth at the site despite the preplant fumigation. Accordingly, we speculate that the reduced impacts of root-lesion nematodes contributed to the improved vigor and fruit yield of trees grown with alfalfa hay mulch.

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Shufu Dong, Denise Neilsen, Gerry H. Neilsen and Michael Weis

A simple flatbed-scanner-based image acquisition system was developed for the measurement of `Gala'/M9 (Malus ×domestica Borkh.) apple tree root growth in rhizoboxes with a transparent acrylic sheet on one side. A tree was planted in the center of each rhizobox, and a modified flatbed scanner was periodically used to directly capture high-resolution digital images of roots growing against the transparent wall. Total root length in the images was either measured manually, or by computer mouse tracing, or automatically with a computer image analysis system. Correlations were made among the different measurements. High quality root images were obtained with the adapted scanner system. Significant linear relationships were found between manual and computer traced root length measurements (r = 0.99), traced and automatic measurements (r = 0.76) and manual and automatic measurements (r = 0.75). Apple roots appeared on the transparent wall 34 days after transplanting, and grew rapidly thereafter, reaching a maximum on the transparent wall 59 days after transplanting. Our results showed that the use of a flatbed scanner for the acquisition of root images combined with computer analysis is a promising technique to speed data acquisition in root growth investigations.

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Katie Palanjian, Luis Valenzuela, Denise Neilsen, Gerry Neilsen and David Eissenstat

As roots change color from white to brown, their absorptivity for water and nutrients typically diminishes. The effects of irrigation on root pigmentation were studied during 2003 and 2004 in Summerland, British Columbia, using an experimental orchard of `Golden Delicious' apple trees on M9 rootstocks. Root pigmentation was monitored weekly over the growing season using a minirhizotron camera inserted into clear plastic tubes in the root zone. Each tree had two emitters, one on either side of the bole and ≈30 cm from the trunk. Four irrigation treatments were tested: full irrigation with replenishing 100% of daily evapotranspiration (ET) on both sides of the tree (100% both), 50% ET irrigation on both sides (50% both), irrigating alternating sides of the tree with 50% ET (50% alternating) and one-sided irrigation at 50% ET (50% one-side). The 50% alternating irrigation treatment simulated the irrigation practice of partial root zone drying where irrigation was alternated about weekly from one side of the tree to the other. Root pigmentation was remarkably fast among these trees, with median days to browning ranging from 4 to 10 days among treatments. For 50% one-side trees, root pigmentation on the dry side of the tree was much faster than roots on the wet side (4 and 7 days, respectively; P< 0.007). Otherwise, no additional significant effects of irrigation on pigmentation were detected.

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Luis R. Valenzuela, Denise Neilsen, Gerry Neilsen and David Eissenstat

New irrigation practices using controlled soil water deficits offer the opportunity of reducing tree vegetative growth and enhancing fruit quality without decreasing fruit size or yield. We tested partial root zone drying (PRD) and deficit irrigation in `Golden Delicious' trees on M9 rootstock, at Summerland, B.C., Canada. There were four treatments: full irrigation (100% daily ET replacement), both sides irrigation (50%daily ET replacement), deficit irrigation (1 side, 50% daily ET replacement) and PRD (alternating sides, 50% daily ET replacement). The purpose of this study was to determine how deficit irrigation and PRD affect above- and below-ground physiology of apple trees where the amount of irrigation was the same. Soil water content, stem water potential, stomatal conductance and transpiration were significantly higher for deficit irrigation than PRD irrigation (P < 0.05) for both years (2003 and 2004). Root dynamics varied among years. For both years, root production was higher in trees under PRD than in trees under deficit irrigation. Root survivorship was significantly higher for trees exposed to PRD treatment than those exposed to deficit irrigation treatment in 2003 (P < 0.0003), but not in 2004 (P > 0.662). Stem growth, fruit yield, and fruit quality were generally not affected by treatments in 2003. In 2004, however, fruit yield was 37% higher in deficit irrigation than in PRD (P < 0.05). Soluble solids and sugar: acid ratio did not differ between these two treatments. For conditions where the amount of irrigation applied was the same, our results suggest that PRD may be less effective than deficit irrigation.

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Gerry H. Neilsen, Denise Neilsen, Peter Toivonen and Linda Herbert

A randomized, complete block, split-plot experimental design with six replicates was established and maintained annually for the first five fruiting seasons (1999 to 2003) in a high-density apple [Malus sylvestris (L) Mill var. domestica (Borkh.) Mansf] orchard on M.9 rootstock planted in Apr. 1998. Main plot treatments involved eight different nutrient regimes, each containing three tree subplots of each of five different cultivars (Ambrosia, Cameo, Fuji, Gala, and Silken). This report compares a +phosphorus (P) treatment, involving annual fertigation at bloom time of 20 g P/tree as ammonium polyphosphate (10N–15P–0K), to a −P treatment. Both treatments also received nitrogen, potassium, and boron nutrients through fertigation. Drip fertigation of P increased 2 M KCl-extractable P to 0.4-m depth within 0.5-m distance of the drippers. Leaf and fruit P concentrations were consistently increased by the +P treatment with few differences among cultivars. P-fertigated trees also had a 20% increase in cumulative yield overall cultivars during the first five fruiting seasons. Standard fruit quality measurements, including fruit size, soluble solids concentration, titratable acidity, and red coloration were unaffected by P application. However, reductions in incidence of water core at harvest, increased resistance to browning, and elevated antioxidant content of harvested fruit measured in some years imply a role for P in apple membrane stability. The cumulative results indicate that applications of 20 g P as ammonium polyphosphate annually at bloom would be advantageous for apples receiving adequate fertigated applications of nitrogen, potassium, and boron. Best apple performance was associated with leaf P concentrations above 2.2 mg·g−1 dry weight and fruit P concentrations between 100 and 120 mg·kg−1 dry weight.