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From March through June 1996, 15N-labeled fertilizer was applied to mature pecan trees [Carya illinoinensis (Wangehn.) K. Koch] in a commercial orchard to determine the fate of fertilizer-N in the tree and in the soil directly surrounding the tree. The concentrations of 15N and total N were determined within various tissue components and within the soil profile to a depth of 270 cm. By Nov. 1996, elevated levels of 15N were greatest at depths just above the water table (280 cm), suggesting a substantial loss of fertilizer-N to leaching. Recoveries of 15N from tissue and soil at the end of 1996 were 19.5% and 35.4%, respectively. Harvest removed 4.0% of the fertilizer-N applied, while 6.5% was recycled with leaf and shuck drop. In 1997, with no additional application of labeled fertilizer, the tissue components continued to exhibit 15N enrichment. By the end of the 1997 growing season, 15N levels decreased throughout the soil profile, with the most pronounced reduction at depths immediately above the water table. Estimated recoveries of 15N from pecan tissue (excluding root) and soil at the end of 1997 were 8.4% and 12.5%, respectively. In 1996 and 1997, 15N determinations indicated an accumulation of fertilizer-N in the tissues and a loss of fertilizer-N to the groundwater. Early spring growth, flowering, and embryo development used fertilizer-N applied the previous year, as well as that applied during the current year.

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The recovery of late-season (September) 15N-labeled fertilizer (N at 55 kg·ha-1) was followed in mature pecan trees [Carya illinoinensis (Wangehn.) K. Koch] and soil (0-270 cm) from 1996 (application year) through 2001 (end of study). Recovery of late-season applied 15N was compared to the recovery of six 15N applications (March through June, N at 221 kg·ha-1) of a previously reported study. By Nov. 1996, both fertilizer schedules exhibited considerable 15N accumulation below the rooting zone and just above the water table (280 cm), with 43.4% and 35.3% 15N recovered from the soil sampling profile of the September and March-June schedules, respectively. 15Nitrogen recoveries from perennial storage tissues (root and wood) were 20.6% and 10.1% under the September and March-June schedules, respectively. The 15N recoveries from annual abscission tissues (leaf, shuck, and nut) were 1.4% and 10.6% under the September and March-June schedules, respectively. By the end of the 2001 growing season, 4% and 9% of the 15N remained in the soil following the September and March-June applications, respectively. Under both fertilizer schedules, >80% of the fertilizer-N was lost to the environment through natural processes and very little was removed during harvest. Nearly 6 years following application, perennial storage of 15N remained greater in the September application (4.3% of the 15N applied) than in the March-June application (2.7% of the 15N applied). Late-season application of fertilizer-N during the kernel filling stage was stored in perennial tissues for use the following year; very little was used for current year growth of annual tissues. Increased accumulation of perennial storage N by late-season application may reduce the depletion of N caused during a heavy-cropping on-year and may moderate the alternate-bearing trend in pecan by providing a greater reservoir of N the following year.

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when studying use of N fertilizer using traditional methods. Nitrogen-14 and nitrogen-15 ( 15 N) are the two stable isotopes of N with atmospheric natural abundances of 99.6337% and 0.3663%, respectively. The latter is an important tracer element in

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leaves of spurs and ES ( Lang, 2001 , 2005 ; Rivera et al., 2016 ). Ayala et al. (2014) reported that foliar application of 15 N-urea after harvest influenced N storage reserves in floral buds for the subsequent spring. Similarly, Ouzounis and Lang

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Previous research on late-season N fertilization of pecans [Carya illinoinensis (Wangehn) K. Koch] has shown significant uptake and storage of N in perennial tissues (roots, trunk, and shoots) that was used in subsequent years. The objectives of this study were to follow the fate of 15N applied at three different stages during pecan kernel fill in both the soil and tree components. In August and September 2002, 15N-labeled ammonium sulfate (9.94% 15N atom excess) was applied (56 kg N/ha) to nine pecan research trees during the early [3 days into kernel fill (DIK)], middle (25 DIK), and late (38 DIK) stages of pecan kernel fill near Las Cruces, N.M. In November 2002, about 67% of applied 15N was recovered from the soil and 13% from tree components. More 15N was recovered in nuts from the early treatment than middle or late treatments. Recoveries for May 2003 were 27% and 60% for tissues and soils, respectively. Leaf recovery increased an average of 14% in May 2003 over November 2002 leaves. More 15N was recovered from the late treatment in all tree components for May 2003 than early or middle treatments. The primary source of N for spring growth was 15N stored in perennial tissues. Fifteen months after 15N fertilizer was applied during kernel fill in 2002 about 24% remained in the soil, 28% had been used by the tree, and 48% was lost to the environment.

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Experiments were conducted from 1985 to 1989 to evaluate the response of radishes (Raphanus sativus L.) to N fertilization on Histosols. Three of these experiments used 15N-labeled fertilizer to evaluate the recovery of N by radishes. There was no response to N fertilization in seven of the eight experiments, even though some of them were conducted under conditions of high rainfall. The one experiment in which radish yields increased with N was conducted in a poorly drained, waterlogged field that was atypical of normal radish production fields. Recoveries of fertilizer N in the marketable radish roots averaged 19%. The results of N and 15N analysis showed that although fertilizer N was available for uptake, so was an ample amount of soil mineralized N. These results indicate that under typical growing conditions, radishes produced on Florida Histosols do not respond to N fertilization.

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Abstract

To study the efficiency of fertilizer use by highbush blueberry (Vaccinium corymbosum L.), four mature ‘Bluecrop’ plants were treated before budbreak (21 Apr.) with soil applications of 15N-enriched urea at a rate equivalent to 40 kg N/ha. Leaf samples were collected at 1- to 4-week intervals during the season and whole plants were harvested at the end of the growing season (22 Sept.). Different plant components were separated, dried, weighed, and analyzed by mass spectrometry. Fertilizer-derived N was observed in leaves 2 weeks after application. The percentage of N from the fertilizer peaked 3 weeks after application (16.5%) and declined to ≈11% shortly thereafter. Plants recovered 32% of applied N by the end of the growing season. Leaves accounted for 32% of this total. Shoot tissue also accounted for 32% of fertilizer-derived N in the plant, with the highest percentage accumulating in young shoots. Less than 15% of fertilizer N remained in the soil at the end of the season.

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Abstract

Translocation of 15N from foliar-applied urea to vegetative and reproductive sinks of avocado (Persea americana Mill, cvs. Fuerte and Hass) was evaluated during inflorescence development and the early stages of fruit set. Urea (2%) increased the number and the total dry weight of the lateral inflorescence per shoot. The concentration of 15N in avocado inflorescences increased proportionately to the concentration of urea applied to the old leaf surface. The amount of 15N translocated was not affected by the proximity of the source leaf to the “terminal” inflorescence. 15N translocated to developing fruit and to new sprouting leaves in similar amount. Urea N was translocated basipetally from current flush leaves to developing fruit. Removing the vegetative sink reduced N influx to the reproductive tissue and increased initial fruit set by a factor of 1.7 to 2.1 in urea-treated and -untreated shoots, respectively. These data indicate that shoot growth does not limit fruit set in avocado via competition for N.

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Abstract

15N-labeled potassium nitrate was applied in a foliar spray to French prune/Marianna 2624 trees (Prunus domestica L.), and the nitrogen absorbed by the leaves was quantified. Nitrogen derived from a single foliar spray averaged 3% of total leaf nitrogen. L77, a non-ionic organosilicone surfactant which lowers surface tensions of aqueous solutions sufficiently for stomatal penetration, significantly enhanced the rate of NO3 absorption and increased incorporation of foliar-derived nitrogen into alcohol insoluble macromolecules. This enhancement was not apparent when labeled NO3 was applied with Regulaid, a carbohydrate-based non-ionic surfactant. About 25% of the foliar-derived N was apparently transported from leaves within 3 days when the stomatal penetrant was employed. No transport was evident in the absence of the penetrant.

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immobilize fertilizer N, it was pretreated 2 months before planting with a liquid fertilizer UAN-32 (32N–0P–0K) at the rate of 0.15 g/L N ( Krewer and Ruter, 2009 ). Treatments. Treatments consisted of applying 10% 15 N labeled fertilizer as ammonium sulfate

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