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Eric J. Hanson

Foliar B sprays (500 mg·liter-1) had increased the B content of apple (Malus domestics Borkh), pear (Pyrus communis L.), plum (Prunus domestics L.), and cherry (Prunus cerasus L.) leaves 90%) to 185% 3 days after treatment. Boron levels in treated apple, pear, and plum leaves decreased to levels similar to nontreated leaves by 9 days after application, whereas cherry leaves required 33 days to approach levels in nontreated leaves. Movement of applied B was also studied by treating cherry leaves with B solutions enriched in the stable isotope, 10B. Isotope analysis indicated that applied B moved out of leaves and into subtending tissues. The highest concentrations of applied B were found in buds, followed by bark and wood.

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Eric J. Hanson

Field trials were conducted in 1988 and 1989 in several Michigan locations to determine if fruit set and yield of sour cherry (Prunus cerasu s L. cv `Montmorency') can be increased by boron (B) applications. Orchards varied in age (6-12 years) and initial leaf B concentrations (18-32 ppm dry weight). Treatments consisted of an unsprayed control and B sprays (500 ppm B) applied to the leaves in Sept. Fall B sprays increased B concentrations in flowers the following spring by 50-100%. The percentage of flowers which set fruit was either unaffected by sprays or increased by as much as 100%.. Fruit yields were unaffected by B sprays in some trials, and increased by as much as 100% in others. No visual symptoms of B deficiency were observed. Results of 1990 trials will also be presented.

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Eric J. Hanson

Seven trials were conducted over 3 years in several Michigan locations to study the response of sour cherry (Prunus cerasus L. cv. Montmorency) to foliar B sprays. Orchards ranged in age (6 to 12 years) and leaf B concentrations (19 to 32 μg B/g dry weight). Treatments consisted of a 500 mg B/liter spray applied to leaves in late September or early October, and an untreated control. Boron sprays increased B concentrations in dormant buds and flowers by 94% and 54%, respectively, but did not consistently change leaf levels. Boron applications increased fruit set and production by as much as 100% in one trial, but had no effect in others. Fruit set and production were most consistently increased in trees containing leaf B levels of 19 to 25 μg·g–1 dry weight. In trees with leaf B concentrations of 25 to 32 μg·g–1, responses to B were less consistent and smaller in magnitude.

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Eric J. Hanson

The effects of multiple calcium (Ca) sprays on berry quality of mature `Bluecrop' plants was tested for two seasons. In 1992, treatments supplied a total of 0, 1.0, 1.9 or 3.8 kg Ca/ha, in five applications between 18 June and 16 July. Calcium was applied as CaCl2. Concentrations for the highest rate ranged from 0.08% Ca in the first spray to 0.2% in the last. In 1993, treatments included a control, 12.1 kg Ca/ha applied as CaCl2, 24.2 kg Ca as CaCl2, and 12.1 kg Ca as the commercial product Nutrical (CSI Chem., Bondurant, IA). Seven sprays were applied between 4 June and 16 July, using concentrations of 0.1% to 0.4% Ca. Treatments had no effect on the percentage of soft or rotten berries, berry firmness, or Ca concentrations in berries in either year. Leaf Ca levels were increased slightly by higher application rates.

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Eric J. Hanson

Calcium sprays were applied to `Bluecrop' highbush blueberry bushes between petal fall and fruit harvest. In 1992, bushes received five sprays between 18 June and 16 July that totaled 0, 1.0, 1.9 or 3.8 kg Ca/ha. Calcium was applied as CaCl2 at spray concentrations of 0.08% to 0.2% Ca. Treatments in 1993 consisted of a control; 12.1 and 24.2 kg Ca/ha as CaCl2; and 12.1 kg Ca/ha as the commercial product Nutrical. Calcium was applied in seven sprays between 4 June and 16 July using spray concentrations of 0.1% to 0.4% Ca. Berry samples were hand-picked, stored for 3 to 20 days, and evaluated. Treatments had no effect on the percentage of soft or rotten berries, berry firmness, or berry Ca concentrations during either year. Calcium applications increased leaf Ca concentrations. Chemical names used: calcium trihydroxyglutarate (Nutrical).

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Eric J. Hanson and Jorge B. Retamales

`Bluecrop' highbush blueberries (Vaccinium corymbosum L.) received various N fertilizer treatments for 5 years. Treatments were evaluated by measuring berry yields and leaf N levels annually and bush size after 5 years. Nitrogen fertilizers increased yields and leaf N levels compared with nonfertilized controls. Split applications of urea (half applied at budbreak, half at petal fall) resulted in 10% higher yields than the same amount in a single application at budbreak. Urea and two controlled-release fertilizers (CRF) with different dissolution rates (3 to 4 months, 8 to 9 months) resulted in similar yields and leaf N levels when compared at the same rate of N. The dissolution rate of the CRF materials did not affect yields or leaf N levels.

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Philip A. Throop and Eric J. Hanson

Absorption of “N-enriched fertilizer by young `Bluecrop' bushes was compared following applications on six dates between April and Sept. Ammonium sulfate solutions containing 2.1 g N (10.2 atom % 15N) were dripped directly into the root zone of single bushes. Soil covers and irrigation were used to maintain similar soil moisture conditions during treatment periods. Bushes were excavated after two weeks of exposure, and separated into roots, stems, and current-season growth (shoots, leaves, fruit). Tissues were dried, weighed, and analyzed for 15N and 14N by mass spectrometry. Bushes treated in May, June and July absorbed a greater percentage of applied N (6-8%) than bushes treated in Apr, Aug or Sept (1-3%). Results indicate that fertilization between late May and late July may result in the greatest efficiency of fertilizer use.

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Eric J. Hanson and G. Stanley Howell

Mature `Concord' vines (Vitis labrusca L.) were excavated at 2- to 4-week intervals through the season to study seasonal changes in vine N concentration. Vine N content began increasing 2 weeks after budbreak, increased most rapidly from mid-May to mid-July, and declined between fruit maturation and the beginning of leaf senescence. Vine N content was lowest at budbreak (18 g) and maximum at fruit maturity (75 g). This change represented a net accumulation of 57 g N/vine or 77 kg N/ha. In a separate study, `Seyval blanc' vines were treated with double 15N-labeled ammonium nitrate at either budbreak or bloom. Labeled N was applied as a spray beneath vines to simulate a broadcast vineyard application. Vines were excavated when leaves began to senesce in October, partitioned into various components, and analyzed by mass spectrophotometry to determine fertilizer-derived N content. Vines had recovered statistically similar percentages of fertilizer N applied at budbreak (7.1%) and bloom (10.6%). The low recovery of fertilizer N likely resulted from the method of fertilizer application, the presence of a competitive grass sod between the rows, and relatively high native soil N levels.

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Philip A. Throop and Eric J. Hanson

Rates of absorption of 15N-enriched ammonium sulfate by young `Bluecrop' highbush blueberries (Vaccinium corymbosum L.) were compared following applications on six dates between late April and September. Ammonium sulfate solutions containing 2.1 g N (10.2 atom % 15N) were dripped directly into the root zone of single bushes. Soil covers and irrigation were used to maintain similar soil moisture conditions during treatment periods. Treated bushes from each application date were excavated after 2 weeks of exposure and separated into roots, stems, and current season's growth (new shoots, leaves, fruit). Tissues were dried, weighed, and analyzed for 15N and 14N by mass spectrometry. Soils were also analyzed for labeled and nonlabeled N. Bushes treated in late May, June, and July absorbed a greater percentage of applied N (6% to 9%) than bushes treated in April, August, or September (1% to 3%). Absorption of N appeared to be affected more by the demand of the plants than soil N availability. Plants absorbed N most efficiently during active growth between late bloom and fruit maturity.

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John A. Cline and Eric J. Hanson

Individual fruit of `Delicious' apple (Malus domestica Borkh.) were exposed to low, high, or ambient relative humidity (RH) levels during different stages of fruit development to study the importance of transpiration and the xylem system in supplying Ca to fruit. The Ca content of fruit exposed to low RH was the same or higher than that of fruit exposed to high RH. Treatments imposed early or late in the season usually affected fruit Ca levels similarly. Fruit weight was not consistently affected by RH treatments. The xylem may be a significant source of fruit Ca throughout the season.