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Ed Stover, Michael Fargione, Richard Risio, Warren Stiles, and Kevin Iungerman

This study was initiated to determine if prebloom sprays of B, Zn, and urea would enhance cropping of apple (Malus×domestica Borkh.) after cold injury, hypothesizing that they may accelerate recovery of damaged vascular tissue. The following foliar nutrient treatments were applied prebloom to `McIntosh' and `Empire' trees at two sites in 1994 and 1995: 1) control; 2) B (22.8 mm) at half-inch-green; 3) Zn-EDTA (0.75 mm) at half-inch-green; 4) B and Zn-EDTA at half-inch-green; 5) B, Zn-EDTA, and urea (59.4 mm) at half-inch-green; 6) B and Zn-EDTA at half-inch-green, followed by B, Zn-EDTA, and urea at pink. In 1994, following a very severe winter that caused visible damage to vascular tissue, `Empire' at both sites cropped more heavily following all treatments that included both B and Zn; such treatments increased cropload by an average of 22% and 35% at the two test sites. Despite a mild winter preceding the 1995 season, prebloom nutrient treatments again increased cropping of `Empire'. In 1996, treatments included a control and a single foliar treatment (B + Zn-EDTA at half-inch-green followed by B, Zn-EDTA, and urea at pink) on `McIntosh' and `Empire' at seven orchard sites. Treatment enhanced cropping in `McIntosh' at three of the seven sites, but there was no effect on `Empire'. Factors influencing differences in response were not apparent from this study, although a complex of factors may be involved. Data for all years indicated that prebloom nutrients did not enhance spur leaf development or fruit set; such treatments probably enhance cropping by increasing retention of flower buds that would otherwise abscise before anthesis. Where cropping was increased, mean fruit weight was not reduced at P ≤ 0.05 but fruit weight was significantly less at P ≤ 0.10 in 1995. Chemical names used: boron (Solubor, disodium octaborate tetrahydrate); zinc (Zn-EDTA, zinc chelate).

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R. Romero-Aranda and J.P. Syvertsen

We compared net gas exchange rates of CO2 and H2O vapor of greenhouse-grown `Duncan' grapefruit (Citrus paradisi Macf.) and `Valencia' orange [C. sinensis (L.) Osbeck] leaves after multiple foliar sprays of urea N with and without NaCl: CaCl2 solutions. Highly saline solutions (3.8 dSm-1) caused necrotic burn symptoms after leaf chloride levels reached 7 mmol·m-2. Grapefruit leaves had higher leaf Cl and more burn symptoms than orange leaves. The remaining green areas of all salt-stressed leaves, however, had similar rates of net CO2 assimilation (ACO2) and stomatal conductance (gs) as water-sprayed control leaves. Total leaf N and chlorophyll increased with repeated foliar applications of urea solutions regardless of salinity levels in the spray solution. Thus, salts in solution did not interfere with foliar absorption of N. High urea N solutions (33.6 g·liter-1) without salts caused foliar burn and leaf abscission after one application. Three sprays of urea-N solution (11.2 g·liter-1) increased N concentration of N-deficient leaves about 60% and increased ACO2 rate about 50%. ACO2 did not increase when nitrogen concentration in leaves exceeded a threshold value of about 200 mmol·m-2 so photosynthetic nitrogen use efficiency (PNUE = ACO2/N) decreased with increasing leaf N concentration. Net gas exchange and PNUE was higher for grapefruit than for orange leaves. Leaf Cl levels from foliar-applied salts may not be as detrimental to leaf gas exchange as Cl from salts in soil-applied irrigation water.

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Qiang Xiao, XiaoHui Fan, XiaoHui Ni, LiXia Li, GuoYuan Zou, and Bing Cao

Pillai, V.N. 1996 Membrane-encapsulated controlled-release urea fertilizers based on acrylamide copolymers J. Appl. Polym. Sci. 60 2347 2351 Agehara, S. Warncke, D.D. 2005 Soil moisture and temperature effects on nitrogen release from organic nitrogen

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Guohai Xia* and Lailiang Cheng

One-year-old `Concord' vines were fertigated with 0, 5, 10, 15, or 20 mm N in a modified Hoagland's solution for 8 weeks during summer. Half of the vines fertigated at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. Four vines from each treatment combination were destructively sampled during dormancy to determine the levels and forms of N and carbohydrates. Nitrogen fertigation during the summer only slightly increased vine N concentration whereas foliar urea application in the fall significantly increased vine N concentration. In response to foliar urea application, concentrations of both free amino acid-N and protein-N increased, but the ratio of protein N to amino acid N decreased. Arginine was the most abundant amino acid in free amino acids and proteins, and its concentration was linearly correlated with vine N concentration. Concentrations of total non-structural carbohydrates (TNC) decreased slightly in response to N supply from fertigation. Foliar urea application in the fall significantly decreased TNC concentration at each N fertigation level. Starch, glucose and fructose decreased in response to foliar urea applications, but sucrose concentration remained unaffected. Approximately 60% of the carbon decrease in TNC caused by foliar urea application was recovered in proteins and free amino acids. We conclude that free amino acids account for a larger proportion of the N in vines sprayed with foliar urea, but proteins remain as the main form of N storage. In response to foliar urea application, part of the carbon from TNC is incorporated into proteins and free amino acids, leading to a decrease in the carbon stored in TNC and an increase in the carbon stored in proteins and free amino acids.

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Guohai Xia and Lailiang Cheng

One-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated with 0, 5, 10, 15, or 20 mm N in a modified Hoagland's solution for 8 weeks during summer. Half of the vines fertigated at each N concentration were sprayed with 3% foliar urea twice in late September while the rest served as controls. Four vines from each treatment combination were destructively sampled during dormancy to determine the levels and forms of N and carbohydrates. Nitrogen fertigation during the summer did not significantly alter vine N concentration whereas foliar urea application in the fall significantly increased vine N concentration. In response to foliar urea application, concentrations of both free amino acid-N and protein-N increased, but the ratio of protein-N to free amino acid-N decreased. Arginine was the most abundant amino acid in free amino acids and proteins, and its concentration was linearly correlated with vine N concentration. Concentrations of total nonstructural carbohydrates (TNC) decreased slightly in response to N supply from fertigation. Foliar urea application in the fall significantly decreased TNC concentration at each N fertigation level. Starch, glucose, and fructose decreased in response to foliar urea applications, but sucrose concentration remained unaffected. Approximately 60% of the carbon decrease in TNC caused by foliar urea application was recovered in proteins and free amino acids. We conclude that free amino acids account for a larger proportion of the N in vines sprayed with foliar urea compared with the unsprayed vines, but proteins remain as the main form of N storage. In response to foliar urea application, part of the carbon from TNC is incorporated into proteins and free amino acids, leading to a decrease in the carbon stored in TNC and an increase in the carbon stored in proteins and free amino acids.

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Pinghai Ding*, Minggang Cui, and Leslie H. Fuchigami

Reserve nitrogen is an important factor for plant growth and fruiting performance in tree fruit crops. The fall foliar urea application appears to be an efficient method for increasing N reserves. The effect of fall foliar urea application on N reserves and fruiting performance were studied with four year old `Gala'/M26 trees grown in 20 gallon containers in a pot-in-pot system from 2001 to 2003 at the Lewis-Brown Horticulture Farm of Oregon State Univ.. The trees were either sprayed with 0 or 2 times 3% urea after harvest in October. Shoot and spur samples were taken at the dormant season for reserve N analysis. Fruit performance was recorded in the following growing season. The fall foliar application significantly increased spur N reserve and had the trend to increase shoot N reserve but not significantly. The fall foliar application significantly increased tree fruit set and cluster fruit set. With normal fruit thinning, fall foliar urea application has the trend to increase both tree yield and average fruit size; without fruit thinning, fall foliar urea application has the trend to increase tree yield. These results indicate that fall foliar urea application an effective method to increase reserve N for maintaining tree yield.

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Y. Suenaga, K. Takamori, F. Nishimot, S. Miyoshi, and T. Higashi

It is not uncommon that tipburns, deformation, and poor coloring of strawberries, delaying of differentiation of flowering buds and flowering, etc., occur reflecting rapid changes in soil solution concentrations by repeated applications of conventional fertilizers. These physiological disorders contribute to lowering the yield and quality of strawberries to a significant extent. Polyolefin coated urea called “MEISTER” is one of the excellent controlled availability fertilizers whose dissolution is primarily controlled by temperature. Therefore, blended materials of a few MEISTER products can supply N matching the plant demand for the long growing season (8 months). This results in contributing to the prevention of occurrences of the physiological disorders described above. Treatment plots using blended materials of MEISTER products were early dissolution, even dissolution, and late dissolution and were fertilized with a single basal application. Compared with the conventional plot, the late dissolution plot was most suitable for strawberry growth, producing the largest yield of high quality. The new fertilization using MEISTER will contribute to decreasing the amount of fertilizer to apply, eliminating topdressing, saving labor cost, etc.

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G.H. Neilsen, P. Parchomchuk, W.D. Wolk, and O.L. Lau

Newly planted `Jonagold' and `McIntosh' apple (Malus domestica Borkh.) on M.26 fertigated with Ca(N03)2 showed increased early tree vigor and leaf Ca concentration but decreased leaf Mg and Mn compared to trees fertigated with urea or NH4N03. Fertigation with P increased early tree vigor, leaf and fruit P concentration, and decreased leaf Mn in the first year relative to a single planting hole application of granular P. Increased fruit Ca concentration in `Jonagold' in one year was associated with the use of Ca(N03)2 and fertigation of P. Fruit quality was generally unaffected by the experimental treatments.

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A.M. Akl, A.M. Wassel, F.F. Ahmed, and M.A. Abdel Hady

This study was performed during the 1991, 1992, and 1993 seasons to study the effect of different concentrations and number of sprays urea and/or boric acid on behavior of buds, vegetative growth, and vine nutritional status of Red Roomy grape vines. Two, three, four, or five sprays for both urea at 0.5%, 1.0%, or 1.5% and/or boric acid at 0.1%, 0.2%, 0.3% in addition to the control treatments were applied. A gradual increase was observed in the percentages of burst and fruiting buds, main branch length, leaf area, cane thickness, total chlorophyll, and total carbohydrates in the leaves and considerable depression was observed in the percentages of dormant and vegetative buds. The most pronounced effect on growth and nutritional status was detected on vines sprayed four times with urea at 1.0% plus boric acid at 0 2% during the growing season.

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A.M. Akl, A.M. Wassel, F.F. Ahmed, and M.A. Abdel Hady

This investigation was conducted during the 1991, 1992, and 1993 seasons to study the effect of different concentrations and number of sprays urea and/or boric acid on yield and berries quality of Red Roomy grapevines. Two, three, four, or five sprays for both urea at 0.5% 1%, or 1.5% and /or boric acid at 0.1%, 0.2%, or 0.3% in addition to the control treatment were applied. Combined sprays of urea and boric acid was preferable in increasing the number of clusters, yield per vine, berry set parentage, fertility coefficient. weight, length and shoulder of cluster, weight and dimensions of berry, total soluble solids, total sugars, and total anthocyanins in grapes and in reducing the percentages of cracked and shot berries and the total acidity compared with the single application of both. Spraying urea at 1.0% in combined with boric acid at 0.2% four times (i.e., at growth start, first bloom, immediately after berry set, and at 30 days later) is recommended for achieving high yield and fairly good berries quality in `Red Roomy' grape vines.