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Gerry Neilsen and Frank Kappel

Leaf nutrient concentration of `Bing' sweet cherry (Prunus avium L.) was affected by rootstock over 4 years in the Pacific Northwest. Trees on GM 79, GI 148/1, GI 195/1, and GI 196/4, which had higher yields than Mazzard, also had lower leaf K and, excepting GM 79, lower leaf Mg concentration. Use of GI 195/1 and 196/4 resulted in lower leaf N than use of Mazzard. These higher-yielding rootstocks will require greater attention to these macronutrients, especially on infertile soil sites. Micronutrient nutrition was little affected by rootstocks, which tended to have the low leaf Zn concentrations typical of irrigated Pacific Northwest orchards. GM 9 and GM 61/1 rootstocks were more dwarfing than Mazzard, with GM 9 leaves having lower K, but higher P, Mg, and Mn concentrations. GM 61/1 had lower leaf concentrations of most nutrients relative to Mazzard.

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Frank J. Peryea, Denise Neilsen, and Gerry Neilsen

The recommendations for boron (B) sprays in deciduous tree fruit orchards have changed little over the past 50 years. We conducted two 3-year field studies evaluating the effect of two modifications to the existing recommendation for B maintenance sprays on apple (Malus ×domestica) tree nutritional status. A widely recommended Na polyborate-based commercial B spray product was used as the B source. Postbloom sprays of B applied at the recommended annual B maintenance rate of 0.56 kg·ha-1 to `Scarlet Gala' apple trees consistently increased fruit B concentration but had a weaker effect on leaf B concentration in early August, the recommended timing for sampling leaves for mineral element analysis. Applying half or all of the annual B maintenance rate in a spray at the pink flowering stage increased flower cluster and early-season leaf B concentrations as well as having positive effects on fruit and leaf B concentrations. The pink sprays increased flower cluster Na concentration but had no effect on leaf and fruit Na concentrations. In the second study, one-quarter of the annual B fertilizer requirement was tank-mixed with each of four biweekly CaCl2 sprays applied starting in early June for bitter pit control. This treatment consistently increased `Scarlet Gala' fruit B concentration but had a lesser effect on August leaf B concentration. It did not interfere with fruit Ca status, and increased both fruit and leaf Na concentrations. Leaf Na concentration in all treatments was substantially lower than levels associated with specific Na toxicity of deciduous fruit trees. The results of these experiments indicate that applying B sprays at the pink flowering stage timing and tank-mixing B with CaCl2 sprays applied for bitter pit control are useful practices to enhance B spray efficacy and convenience of application.

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Gerry Henry Neilsen, Denise Neilsen, and Linda Herbert

A randomized complete block, split-plot experiment with six replicates was established and maintained for the first six fruiting seasons (1999 to 2004) in a high-density apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] orchard on M.9 rootstock planted in Apr. 1998. This report assesses responses to six main-plot fertigation treatments, each containing three tree subplots of five different cultivars (Ambrosia, Cameo, Fuji, Gala, and Silken). Fertigation treatments were a factorial combination of two nitrogen (N) rates and three N application timings. N was applied at low (28 mg N/L) or high (168 mg N/L) concentrations daily at 0 to 4, 4 to 8, or 8 to 12 weeks after full bloom (wafb). Under greater N inputs, all cultivars had increased midsummer leaf and harvested fruit N concentrations, decreased fruit firmness, and in heavy crop years, decreased percent red color. Annual yield of all cultivars was significantly increased by N rate in a single year, but their cumulative yields were not different between treatments as a result of rate or timing. Altering the timing of N application within 12 wafb only affected leaf and fruit tissue N concentration. Leaf N was higher after 4 weeks of fertigation any time, although concentrations declined over the growing season, reaching minimum values around harvest. Fruit N was increased by fertigation 4 to 12 wafb. Yield, fruit firmness, and color were unaffected by fertigation timing. Critical fruit quality issues for ‘Gala’ and ‘Silken’ were small fruit size, for Ambrosia low fruit numbers, and for ‘Cameo’ soft fruit. ‘Fuji’, which achieved high yield and leaf N concentration and firm fruit, had poor red color regardless of N treatments.

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Gerry Neilsen, Frank Kappel, and Denise Neilsen

`Lapins' sweet cherry (Prunus avium L.) trees on Gisela 5 (Prunus cerasus × Prunus cansecens) rootstock were maintained for the first four growing seasons with eight different fertigation treatments. Treatments involved N application at low (42 mg·L-1), medium (84 mg·L-1), and high (168 mg·L-1) concentrations via sprinkler-fertigation of Ca(NO3)2 each year about 8 weeks after bloom. The medium N treatment was also applied with P fertigation in early spring or with K fertigation in June. Nitrogen was also broadcast in early spring at 75 kg·ha-1 or followed with medium N sprinkler-fertigated postharvest in August. As a final treatment the medium root zone N concentration was maintained for 8 weeks postbloom via drip fertigation. Throughout the study, irrigation was scheduled to meet evaporative demand based on an electronic atmometer. Drip fertigation, which wet a smaller portion of the orchard floor, considerably reduced per-tree water applications. Tree vigor and pruning weights were reduced for drip-fertigated as compared to sprinkler-fertigated trees although cumulative yield was not significantly different during the study. Fruit size, however, was smaller for this treatment when crop load was at a maximum at year 4. Future research is warranted to insure fruit size can be maintained for heavily cropping drip-fertigated trees. Leaf and fruit N increased linearly as N concentration of sprinkler-fertigating solution increased from low to high values. Optimum yield and highest fruit quality were associated with the medium N treatment. Sprinkler fertigation of P and K did not increase leaf and fruit concentration of either nutrient or meaningfully affect tree performance.

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Gerry Neilsen, Frank Kappel, and Denise Neilsen

‘Lapins’ sweet cherry (Prunus avium L.) on Gisela 5 (Prunus cerasus × Prunus canescens) rootstock were subjected to a factorial combination of two crop load and eight fertigation treatments from the sixth to the eight growing seasons. Crop load treatments included full crop and dormant spur thinning to remove and maintain 50% of fruiting spurs. The eight fertigation treatments, which had been maintained since the first growing season, included low (42 mg·L−1), medium (84 mg·L−1), and high (168 mg·L−1) concentrations of N applied by sprinkler fertigation of Ca(NO3)2 annually ≈8 weeks postbloom. The medium N concentration was also applied with P fertigated in early spring or K fertigated in June. A standard N treatment involved broadcast application of NH4NO3 in early spring at 75 kg·ha−1 also followed with medium N sprinkler-fertigated postharvest in August. The medium N concentration was also supplied for 8 weeks postbloom through drip emitters. Removal of 50% of fruiting spurs decreased annual yield on average by only 10%. Average fruit size could be increased in years of high crop load (greater than 400 g fruit/cm2 trunk cross-sectional area), but in a year of low crop load (less than 100 g fruit/cm2), fruit size was very large (averaging greater than 14 g) and unaffected by crop load adjustment. Minimal effects on fruit and leaf NPK concentrations, fruit firmness, soluble solids concentration (SSC), and titratable acidity (TA) were associated with yield reductions of 10%. Fertigation treatments resulted in a large range in tree vigor and yield during the experiment. High N applications reduced tree and fruit size and fruit TA and were undesirable. Annual P and K fertigation by sprinklers was generally ineffective, having minimal effects on tree PK nutrition and fruit quality with the exception of increased fruit firmness associated with P fertigation in 2005, when yield was low. Drip-fertigated trees were small, frequently had fruit with elevated SSC, but had deficient leaf K concentrations in 2004 implying a need to fertigate K when drip-irrigating.

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Kelly Ross, Gerry Neilsen, and Denise Neilsen

This work examined the effect of irrigation frequency and phosphorus (P) fertigation on the levels of phenolic compounds present in two sweet cherry cultivars, ‘Skeena’ and ‘Cristalina’, over three growing seasons (2012–14). Two irrigation treatments were tested: a high irrigation frequency (I1) and a low irrigation frequency (I2). Both irrigation treatments applied the same quantities of water [100% evapotranspiration (ET)], but the high irrigation frequency applied water four times daily (0300, 0900, 1500, and 2100 hr) whereas the low irrigation frequency was applied at one time (0900 hr) every second day. Three soil management treatments were investigated, including 1) an unmulched control receiving no P, 2) a 10-cm waste wood mulch receiving no P, and 3) a treatment involving annual fertigation of 20 g P/tree at full bloom as ammonium polyphosphate. It was determined that cultivar was the most important factor affecting levels of phenolic compounds in sweet cherries, with generally greater levels associated with ‘Skeena’. The effect of different irrigation and fertilization strategies showed less promising results in terms of influencing levels of phenolic compounds. Both severe and mild water stress did not show an appreciable influence on increasing levels of phenolic compounds in cherries. Furthermore, severe water stress, which occurred during 2012, was associated with the lowest annual concentration of phenolic compounds and an economically unacceptable reduction in fruit size. Phosphorus fertigation influenced cherry phosphorus status positively by increasing leaf and fruit P concentrations consistently, yet these fruit exhibited lower levels of phenolic compounds.

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Gerry Neilsen, Peter Parchomchuk, Michael Meheriuk, and Denise Neilsen

Various schedules of 40 g N and 17.5 g P/tree per year were applied with irrigation water (fertigation) to `Summerland McIntosh' apple (Malus ×domestica Borkh.) trees on M.9 rootstock commencing the year of planting. Leaf K concentrations averaged 0.82% dry mass, indicating deficiency, by the third growing season. This coincided with extractable soil K concentrations of 50-60 μg·g-1 soil in a narrow volume of the coarse-textured soil located within 0.3 m of the emitters. The decline in leaf K concentration was reversed and fruit K concentration increased by additions of K at 15-30 g/tree applied either as granular KCl directly beneath the emitters in spring or as KCl applied as a fertigant in the irrigation water. K-fertilization increased fruit red color, size, and titratable acidity only when leaf K concentration was <1%. Fruit Ca concentration and incidence of bitter pit or coreflush were unaffected by K application. NPK-fertigation commencing upon tree establishment is recommended for high-density apple orchards planted on similar coarse-textured soils.

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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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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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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.