Comparative movement of labelled nitrogen and zinc in 1 ... - INTA

Journal of Horticultural Science & Biotechnology (2006) 81 (5) 839–844
Comparative movement of labelled nitrogen and zinc in 1-year-old
peach [Prunus persica (L.) Batsch] trees following late-season foliar
application
By E. E. SANCHEZ 1 , S. A. WEINBAUM 2 and R. S. JOHNSON 3 *
1 INTA, Alto Valle, CC 782, 8332 General Roca, Argentina
2 Department of Plant Sciences, One Shields Ave, University of California, Davis, CA 95616, USA
3 Department of Plant Sciences, University of California, UC Kearney Agricultural Center,
9240 South Riverbend Avenue, Parlier, CA 93648, USA
(e-mail: sjohnson@uckac.edu) (Accepted 7 June 2006)
SUMMARY
Late in the season, a double-labelled solution containing 15 N-enriched urea and 68 Zn sulphate was painted on the
entire leaf area of 15, 1-year-old ‘O’Henry/Nemaguard’ peach trees to quantify N and Zn movement out of leaves
following foliar application, and redistribution of these nutrients to new growth in the following Spring. About 47%
of the labelled N and only 7% of the labelled Zn painted on the leaf surfaces was recovered in the permanent structure
of the trees after leaf fall. Thus, it is concluded that foliar applications of Zn in the Autumn are not very efficient at
supplying Zn to peach trees, especially when compared to supplying N as urea sprays in the Autumn. These data raise
the possibility that foliar applications of Zn may actually be considered as soil applications, because 90% or more of
the foliar-applied Zn may be carried to the orchard floor at the time of leaf fall. Therefore, future research needs to
focus on assessing the efficacy of foliar applications for Zn nutrition of fruit trees, and identification of potentially
detrimental effects from possible excessive soil accumulation of Zn. Once within the tree, however, labelled Zn was
quite mobile and was stored throughout the plant, including in the roots. Of the labelled N and Zn exported from
treated leaves prior to leaf fall, a substantial redistribution from storage was evident by 2 weeks after bloom and, by
4 weeks after bloom, 38% and 56% of the labelled N and Zn, respectively, had been redistributed from storage in
roots, trunk and 1-year-old shoots to new growth. The biomass of new, above-ground growth tripled between 2 – 4
weeks after bloom and was coincident with a conspicuous influx of both N and Zn from the soil.
Zinc is considered to be the most widely-limiting
micronutrient for tree fruit production (Swietlik,
1999). Deficiencies are common in the sandy and
alkaline soils which are typical of many of California’s
fruit growing districts. Inadequate availability of zinc in
soils has resulted in the large-scale adoption of annual
foliar applications of zinc.
Post-harvest and dormant foliar sprays of Zn have
been recommended for deciduous fruit trees in many
production areas (Swietlik and Faust, 1984; Neilsen and
Neilsen, 1994). In California, it is estimated that a large
percentage of fruit and nut orchards are sprayed every
Autumn with Zn to increase tree Zn reserves.
Previous research suggested that the effects of these
sprays are short-lived, due to limited translocation of the
absorbed Zn. Thus, post-harvest applications of zinc to
‘Bramley’ apple (Malus domestica Borkh.) trees did
not increase Zn levels in flower receptacles in the Spring
following treatment (Hipps and Davis, 2001). Similar
results were reported by Sánchez and Righetti (2002) on
‘Jonagold’ apple trees. Swietlik and Zhang (1994)
reported that foliar-applied Zn was not translocated to
the roots of sour orange (Citrus aurantium L.) trees and,
thus, could not remediate Zn-deficiency in the roots.
*Author for correspondence.
To measure Zn movement out of treated leaves
accurately, it is necessary to use either radioactive 65 Zn or
the stable isotope 68 Zn. Unfortunately, few studies on
fruit trees have been undertaken with Zn isotopes.
Grauke et al. (1982) treated the abaxial and adaxial
surfaces of immature and mature pecan [Carya
illinoensis (Wang.) K. Koch] leaves with ZnSO4 and Zn
(NO3) 2 plus NH 4NO 3 and urea, both the former labelled
with 0.3 µCi 65 Zn, to study the uptake and translocation
of Zn. They reported some Zn translocation, but the
limited extent of movement could not ensure adequate
availability of Zn for new growth.
Zhang and Brown (1999) reported 14 – 15% recovery
of foliar-applied 68 Zn, after washing, in immature
pistachio (Pistacia vera L.) leaflets 3 – 10 d after
application. The absorption and transport of foliarapplied
Zn were much lower for mature than for
immature leaflets. Mature leaflets translocated 2% of the
applied Zn, while immature leaflets translocated 6.5%.
Similar patterns of absorption and translocation of
foliar-applied Zn were observed in field trials (Brown
et al., 1994).
In avocado, 65 Zn was not translocated from spots
applied to intact leaves, to adjacent parenchyma tissue
(Kadman and Lahav, 1979). Also, in ‘Hass’ avocado,
experiments in which 65 Zn was applied to leaves of

840
greenhouse-grown seedlings showed that less than 1% of
the Zn applied as ZnSO 4 or as Zn metalosate was
absorbed by the leaf tissue.
In apples, studies using both unlabelled Zn and the
stable isotope, 68 Zn, demonstrated that neither dormant
nor Autumn applications contributed significantly to the
Zn content of newly-developing tissues in the Spring
(Sánchez and Righetti, 2002). However, Spring
applications of Zn affected only those leaves contacted,
and very little Zn moved from the sprayed leaves to new
organs.
Thus, it appears that foliar-applied Zn is rather
immobile. The fact that symptoms of Zn deficiency are
clearly visible in new growth is consistent with the
limited mobility of Zn applied to mature foliage. Thus,
the efficacy of Zn application will depend on the
percentage of tree leaf area that receives the Zn spray,
and on the physiological age of the foliage exposed.
Up to now, no attempts have been made to quantify
the amount of Zn delivered to storage tissues after foliar
application, or to assess the portion of the storage pool of
Zn that is remobilised into new growth the following
Spring. In contrast to Zn, the relatively high N-use
efficiency of foliar urea sprays has been welldocumented
in many fruit species (Weinbaum, 1988;
Rosecrance et al., 1998;Tagliavini et al., 1998;Toselli et al.,
2004). However, an assessment of N-recovery in the
following season, after a late season application of urea,
has not been quantified under orchard conditions in any
fruit tree species.
Our objectives were (i) to quantify the movement of N
and Zn out of leaves following foliar application; (ii) to
quantify the distribution of N and Zn in the permanent
structures of the dormant tree; and (iii) to quantify the
redistribution of foliar-applied N and Zn from the tree
structure to new growth in the following Spring. The
relative contribution of the movement of foliar-applied
Zn to the storage pool should permit a more quantitative
perspective on the value of foliar applications of Zn.
MATERIALS AND METHODS:
In Spring 2003, dormant, nursery-grown peach trees of
cv. ‘O’Henry/Nemaguard’ were planted in a sandy loam
soil of the Hanford series (typic xerothents) at the
University of California Kearney Agricultural Center,
Parlier, California (36°48’ N, 119°30’ W). The trees were
trained to a Kearney Perpendicular “V” system (DeJong
et al., 1994) with two main scaffolds. All shoots not
arising from the scaffolds were removed in late Summer.
On 11 September 2003, five replicates of three uniform
trees that had grown to a height of approx. 1.5 m were
selected for treatment.
Ten ml of a ZnSO4 solution containing 68 Zn (99.4
Atom % 68 Zn) at 1 mg ml –1 plus 15 N-labelled urea (10.8
Atom % 15 N) at 2% (w/v) was applied with a small paint
brush to the adaxial leaf surface of the entire canopy on
each of the 15 trees. Before application, the trunks and
soil were covered with plastic to prevent contamination
by labelled Zn and N from the treated leaves, although
care was taken to prevent the labelled solution from
dripping or running-off the leaves. As the trees were still
growing, a second application of 3 ml per tree, mostly to
the new growth, was made on 29 October 2003, following
Foliar application of labelled N and Zn in peach
the same procedure. A total of 13 ml per tree was thus
applied in two applications. Senescent leaves were
collected on tarpaulins placed under the trees and
subsequently removed from the orchard to avoid any
possible contamination. During dormancy (16 January
2004), one tree from each replicate was excavated and
separated into roots, trunk and shoots. Backhoe trenches
2.0 m deep were dug 1.5 m from the trunk and the soil
around the roots was removed with a pitchfork. We
estimated ≥ 90% recovery of root biomass. The two
remaining trees in each replicate were excavated on two
dates in Spring 2004. All trees were left unpruned
between the time of Zn/N application and excavation, to
minimise variation between trees and to maximise the
recovery of both isotopes. The first Spring excavation
was on 22 March, 2 weeks after full bloom, and the
second excavation was on 5 April, approx. 4 weeks after
full bloom. In both Spring excavations, the trees were
divided into roots, trunk, shoots and new growth.
Trunks were cut at the graft union, and roots were
washed with water at the excavation site. After tissue
separation, all fresh materials was taken to the laboratory
and washed. Tissues were cut into smaller pieces to
facilitate drying, placed in paper bags, dried at 60°C for at
least 48 h, and ground to pass a 40-mesh screen. Dry
tissue (0.5 g) was digested using a nitric acid-hydrogen
peroxide microwave digestion to produce a liquid sample
for total Zn and N isotope analysis (Sah and Miller, 1992).
Sample analysis
Digested plant samples were analysed using an
Agilent Technologies 7500c ICP-MS (Agilent
Technologies, Palo Alto, CA, USA). The Zn isotopes
measured were 64, 66, 67, 68 and 70. Each isotope was
monitored for 900 ms with a total of ten replicates per
analysis. Yttrium (0.5 µg l –1 ) was added as an internal
standard to each blank, each calibration standard, and
each plant sample. Calibration reference Zn standards
(SPEX CertiPrep, Metuchen, NJ, USA) ranged from 5 ng
ml –1 to 5 µg ml –1 total Zn (Zhang and Brown, 1999).
To calculate isotopic concentrations, the ion intensities
of each Zn isotope were first standardised with the signal
of the internal standard. The abundance of each isotope
was then determined by normalising each Zn isotope
ratio to the total amount of Zn measured in the sample.
Isotopic concentrations were calculated using calibration
curves for each Zn isotope and the abundance of that
isotope in the sample. The enrichment of 68 Zn was
evaluated using the 68 Zn/ 67 Zn ratio, which was calculated
using the ion intensities (Zhang and Brown, 1999).
Standard solutions were analysed throughout the
sample run and used to apply a mass discrimination
correction factor to all samples. This correction factor
was the ratio of the measured 68 Zn/ 67 Zn ratio to the
theoretical ratio, and ranged from 0.9944 – 1.0249.
The amount of Zn derived from the labelled fertiliser
was calculated from the equation based on the isotope
ratio modified from Ziegler et al. (1989), described in
detail by Zhang and Brown (1999).
Nitrogen isotope composition was determined by
mass spectrometry. Atom percentage values of 15 N were
converted to N derived from the labelled fertiliser using
standard conversions (Hauck and Bremer, 1976).
Results for dry mass (DM) and the distribution of

TABLE I
Biomass distribution (g DW tree –1 ) among organs of trees sampled during
dormancy (16 January), 2 weeks after full bloom (22 March) and 1 month
after full bloom (5 April)
Organ January 16 March 22 April 5
New Growth – 112.8 ± 22.6 339.4 ± 34.9
Shoots 292.0 ± 39.9 a
total and labelled Zn and N are reported as means ±
standard deviation for all components. Percentage
distributions of total and labelled Zn and N for each
tissue and sampling date were analysed by the paired
Student’s t test. Percentage values were arcsin
transformed before statistical analysis. Recovery of Zn
and N was calculated as a percentage of the total
application of 68 Zn and 15 N isotopes.
RESULTS
Almost 55% of the total DM of dormant, 1-year-old
trees corresponded to roots, 18% to the trunk, and 27%
to shoots (Table I). Two weeks after full bloom (22
March 2004), the second batch of trees was excavated,
and the total tree weights had not increased over the 65 d
since the previous, dormant season excavation (Table I).
The main difference in DM distribution between the first
and second excavated trees was in the roots. Roots, as a
percentage of tree DM, decreased from 55% during
dormancy to about 45% and 34%, 2 weeks and 4 weeks
after full bloom, respectively. As new growth increased,
tree DM increased by approx. 20% between dormancy
and 1 month after full bloom (Table I).
Total N content increased from 15 g to 26 g per tree
between dormancy and 1 month following full bloom.
Total Zn content increased from 11 mg to 20 mg per tree
during the same period (Table II). Most of the uptake of
N and Zn from the soil between dormancy and 4 weeks
after full bloom occurred over the 2 week period from
E. E. SANCHEZ,S.A.WEINBAUM and R. S. JOHNSON
223.8 ± 7.1 310.0 ± 41.3
Trunk 199.2 ± 54.6 204.0 ± 26.3 210.2 ± 30.0
Roots 603.4 ± 81.0 437.8 ± 23.2 442.4 ± 81.7
Whole Tree 1094.6 ± 145.5 978.4 ± 130.4 1302.0 ± 140.4
a
Values are means ± SD. (n = 5 trees).
841
2 – 4 weeks after bloom. The roots of dormant trees
contained 70% and 41% of total tree N and Zn contents
respectively, at the time when roots comprised 55% of
the tree biomass (Table III).
In the second excavation, 2 weeks after bud break (22
March), the total N and Zn contents per tree remained
relatively unchanged from the levels determined
previously in dormant trees. The fact that, in these trees,
new growth contained 34% and 38% of the total pool of
N and Zn, respectively, 2 weeks after bud break (Table
III), indicates the substantial intra-tree redistribution of
nutrients that occurs during this period.
Recovery of labelled N and Zn applied to trees varied
from 45.3 – 49.2% and from 6.8 – 7.9%, respectively
(Table IV). These data did not include the 15 N and 68 Zn
retained in senescent leaves, as our aim was to quantify
the amount of foliar-applied nutrient translocated from
leaves to storage in perennial parts of the tree over the
Winter.
Both elements were translocated throughout the trees
after application. Sixty-five percent of the labelled N, and
42% of the labelled Zn were found in roots during
dormancy (Table V). Two weeks after full bloom, 24% of
the labelled N and 45.5% of the labelled Zn had been
translocated to new growth and, by 4 weeks after full
bloom (5 April), the storage pool had contributed 38%
and 55.9% of N and Zn, respectively, to the new growth.
A striking quantitative difference was apparent between
the two nutrients in their re-translocation from storage
to new growth. Roots remobilised 30% of stored N to the
new growth, and 79% of stored Zn (Table IV). As a
result, the amount of labelled N in roots decreased from
65% to 43.8% of the tree total, and labelled Zn
decreased from 42% to 7.7% of the tree total 1 month
after full bloom (Table V).
DISCUSSION
Previous studies applying 68 Zn to a single leaf or group
of leaves in fruit trees have suggested limited mobility
(Zhang and Brown, 1999; Sánchez and Righetti, 2002).
TABLE II
Total tree N (g N tree –1 ) and Zn (mg Zn tree –1 ) distributions among different organs of trees sampled during dormancy (16 January), 2 weeks after full
bloom (22 March) and 1 month following full bloom (5 April)
January 16 March 22 April 5
Organ N Zn N Zn N Zn
New Growth – – 5.70 ± 1.21 4.55 ± 0.86 14.93 ± 1.60 11.32 ± 0.98
Shoots 3.30 ± 0.44 a
4.51 ± 0.78 1.82 ± 0.55 2.95 ± 1.26 2.15 ± 0.24 4.26 ± 0.50
Trunk 1.20 ± 0.35 2.27 ± 0.75 0.89 ± 0.16 1.95 ± 0.79 0.85 ± 0.14 2.13 ± 0.66
Roots 10.79 ± 1.95 4.66 ± 0.36 8.24 ± 0.49 2.69 ± 0.39 7.94 ± 1.29 2.11 ± 0.49
Whole Tree 15.29 ± 2.50 11.44 ± 1.78 16.65 ± 2.05 12.13 ± 2.75 25.87 ± 2.49 19.83 ± 2.26
a
Values are means ± SD (n = 5).
TABLE III
Percentage distribution of total tree N and Zn among different organs of trees sampled during dormancy (16 January), 2 weeks after full bloom
(22 March) and 1 month after full bloom (5 April)
January 16 March 22 April 5
Organ N Zn Sig. N Zn Sig. N Zn Sig.
New Growth – – – 34.0 ± 3.5 37.9 ± 3.1 NS 57.7 ± 2.71 57.3 ± 2.0 NS
Shoots 21.8 ± 2.3 a
39.4 ± 2.8 ** b
10.7 ± 2.1 23.6 ± 5.6 ** 8.4 ± 1.1 21.5 ± 1.8 **
Trunk 7.8 ± 1.9 19.5 ± 3.2 ** 5.4 ± 0.6 15.8 ± 4.3 ** 3.3 ± 0.5 10.6 ± 2.6 **
Roots 70.4 ± 2.2 41.1 ± 3.9 ** 49.9 ± 5.3 22.7 ± 4.0 ** 30.6 ± 3.6 10.6 ± 1.5 **
Whole Tree 100.0 100.0 100.0 100.0 100.0 100.0
a
Values are means ± SD (n = 5).
b
NS, **, non-significant, or significant at P ≤ 0.01, respectively, by paired t test.

842
However, such studies could not simulate complete foliar
application, in which all leaves, shoots and trunk of the
tree are treated, nor quantify the percentage
redistribution of Zn and N from over-Winter storage to
new growth the following Spring. Furthermore, no
previous studies on fruit trees have identified the parts
which serve as sites of for Zn deposition over Winter
On the other hand, the dynamics of uptake of foliar N
by trees has been widely reported (Rosecrance et al.,
1998; Tagliavini et al., 1998; Weinbaum, 1988). Thus
inclusion of labelled N in the applications allowed us to
compare N with Zn, to gain better information on their
comparative partitioning to storage organs, their
redistribution after the resumption of growth in Spring,
and identification of probable source organs for nutrient
allocation into new growth.
By treating the entire canopy, we were able to quantify
the amounts and percentages of labelled N and Zn
applied to leaves that were translocated out prior to leaf
abscission. Between 45.3 – 49.2% of N, and 6.7 – 7.8% of
Zn was recovered in the trees after leaf fall. The 15 N and
68 Zn recovered in new Spring growth had been foliarly
applied the previous Autumn, stored during the Winter,
and remobilised in the Spring. These data should be
considered as the minimum percentage redistribution of
N and Zn from storage organs to new growth, because
our experiment was terminated 4 weeks after full bloom.
We cannot rule out the possibility of additional nutrient
redistribution from storage if the experiment had been
extended into the growing season .
Using 15 N-labelled urea, Tagliavini et al. (1998)
demonstrated 58 – 69% absorption of the urea-N
intercepted by the canopies of nectarine [Prunus persica
(L.) Batsch var. nectarina] trees. We did not analyse
senescent leaves, but recognise that additional recovery
of foliar-applied N in these leaves was likely, as complete
export of urea-N prior to leaf senescence was not
anticipated. Other studies have shown N recovery rates
in the permanent structure of the tree of 50% or better
after an Autumn foliar application of 15 N-labelled urea
Foliar application of labelled N and Zn in peach
TABLE IV
Distribution of labelled N and Zn (mg tree –1 ) among different organs of trees sampled during dormancy (16 January), 2 weeks after full bloom
(22 March) and 1 month after full bloom (5 April), and percentage recovery of total isotope applied
January 16 March 22 April 5
Organ N Zn N Zn N Zn
New Growth – – 13.01 ± 1.78 0.397 ± 0.06 22.30 ± 1.87 0.568 ± 0.069
Shoots 13.58 ± 1.02 a
0.425 ± 0.053 7.56 ± 2.7 0.232 ± 0.072 7.28 ± 0.06 0.296 ± 0.04
Trunk 6.31 ± 1.74 0.107 ± 0.03 4.24 ± 0.94 0.081 ± 0.017 3.32 ± 0.31 0.073 ± 0.022
Roots 37.22 ± 4.02 0.385 ± 0.027 29.38 ± 1.14 0.166 ± 0.028 26.0 ± 5.39 0.079 ± 0.017
Whole Tree 57.11 ± 4.84 0.918 ± 0.074 54.19 ± 5.89 0.876 ± 0.137 59.89 ± 6.58 1.016 ± 0.100
RECOVERY (%) 47.75 ± 4.05 7.10 ± 0.57 45.31 ± 4.93 6.78 ± 1.06 49.24 ± 5.50 7.86 ± 0.78
a
Values are means ± SD (n = 5).
(Weinbaum, 1988; Rosecrance et al., 1998).
In the present study, we were unable to determine how
much of the labelled Zn deposited on the leaf surfaces
was actually absorbed by the leaves. Nevertheless, 7 – 8%
transport is approx. the same percentage translocation as
has been reported in other crops (Boaretto et al., 1998;
Ferrandon and Chamel, 1988; Zhang and Brown, 1999).
Some workers have even reported less than 1%
translocation (Boaretto et al., 2002; Volschenk et al.,
1999). Presumably, Zn transport levels less than 10%
might be considered the maximum that can be achieved
with standard sprays of ZnSO4. There are significant
barriers to the absorption of foliar-applied Zn. Zn can be
adsorbed to the cuticle and/or cell walls (Ferrandon and
Chamel, 1988), or sequestered in an insoluble form
(Zhang and Brown, 1999) and thus made unavailable for
transport.
Partitioning of N to the root system in Autumn, for
storage during the Winter, is well-documented in
perennial trees (Sánchez et al., 1992; Millard, 1996), but
no similar data on Zn are available in the literature.
Sixty-five percent of the recovered, labelled N was
transported to the roots in this experiment (Table V).
Although not as much as N, 42% of the recovered 68 Zn
was found in dormant roots (Table V), suggesting good
mobility of the small amount of leaf-absorbed Zn in
peach trees. This contrasts with citrus, where several
studies have shown limited movement of foliarly-applied
Zn to roots (Swietlik, 2002a, b).
In the Spring, trees had remobilised approx. 24% of
their 15 N and 45.5% of their 68 Zn for new growth 2 weeks
after full bloom. By the end of the experiment, 4 weeks
after full bloom, remobilisation had increased to around
38% and 55.9% of tree 15 N and 68 Zn, respectively (Table
V). Remobilisation of 15 N and 68 Zn was mainly from
roots and shoots. Roots were particularly important for
supplying Zn, as 79% of the 68 Zn in roots moved into
new growth, compared to only 30% for 15 N (Table IV).
Once again, this supports our conclusion that Zn from
foliar sprays is reasonably mobile in peach trees. In fact,
TABLE V
Percentage distribution of total labelled N and total labelled Zn among the different organs during dormancy (16 January), 2 weeks after full bloom
(22 March), and 1 month after full bloom (5 April)
January 16 March 22 April 5
Organ N Zn Sig. N Zn Sig. N Zn Sig.
New Growth – – – 24.0 ± 1.3 45.5 ± 3.9 ** 38.0 ± 2.6 55.9 ± 3.1 **
Shoots 24.0 ± 3.2 a
46.3 ± 3.0 ** b
13.7 ± 3.6 26.2 ± 5.3 ** 12.5 ± 2.1 29.2 ± 3.6 **
Trunk 11.0 ± 2.7 11.7 ± 3.0 NS 7.8 ± 0.9 9.2 ± 1.2 NS 5.7 ± 0.8 7.2 ± 2.0 NS
Roots 65.0 ± 2.2 42.0 ± 2.9 ** 54.6 ± 4.9 19.1± 3.5 ** 43.8 ± 4.3 7.7 ± 1.3 **
Whole Tree 100.0 100.0 100.0 100.0 100.0 100.0
a
Values are means ± SD (n = 5).
b
NS, **, non-significant, or significant at P ≤ 0.01, respectively, by paired t test.

in early Spring, Zn appears to be even more readily
available than N.
The question of Zn mobility in plants is controversial.
Early observations suggested that Zn was quite
immobile; however, recent studies have demonstrated
extensive phloem mobility of Zn in wheat (Garnett and
Graham, 2005; Haslett et al., 2001; Page and Feller, 2005).
At present, it appears that Zn may exhibit variable
mobility (Longnecker and Robson, 1993). Experiments
with apple have shown no or little movement of Zn from
the leaf receiving the application (Orphanos, 1975);
however, wheat experiments have shown extensive
mobility throughout the plant (Haslett et al., 2001). Some
of these differences may be due to species differences.
The degree of mobility could also be influenced by the
Zn status of the plant, thus deficient plants would not
remobilise Zn well (Longnecker and Robson, 1993); and
by the stage of plant development (Millikan et al., 1969).
For instance, in wheat, where Zn mobility has been
studied extensively, Zn appears to be quite immobile in
young growing plants. However, when flowering and
seed formation begin in mature plants, Zn mobility is
increased. Senescing wheat leaves export more than 50%
of their Zn to developing seeds (Garnett and Graham,
2005).
One important, practical question is whether a foliar
spray of Zn, under the conditions in our experiment,
could effectively supply the Zn needs of a growing peach
tree in the Spring. By 1 month after bloom, only about
5% of Zn in the new growth was derived from the foliar
application in the Autumn. This is insufficient to
maintain vigorous growth, if root uptake is limited.
However, the concentration of Zn used in our
experiment (1 mg ml –1 ) is considerably less than typical
recommended rates of 11 – 17 kg ZnSO4 (36% Zn) ha –1
(Johnson and Uriu, 1989). Assuming an application rate
of 830 l ha –1 , this range of recommended rates would
provide 4 – 6 mg ml –1 Zn. In addition, 68 Zn was applied
only to the adaxial sides of the leaves. Thus, with higher
concentrations applied both to the adaxial and abaxial
leaf surfaces, it is conceivable that 8 – 12 times more Zn
could be supplied to the tree. However, even that
amount would still only provide 40 – 60% of the total
amount in the new growth. Therefore, it appears that
BOARETTO, A. E., OLIVEIRA, M. W., MURAOKA, T. and NASCIMENTO
FILHO, V. F. (1998). Absorption and translocation of 65 Zn
applied to common bean leaves. Journal of Nuclear Agricultural
Biology, 27, 225–230.
BOARETTO, A. E., BOARETTO, R.M.,MURAOKA, T., NASCIMENTO
FILHO, V. F., TIRITAN, C. S. and MOURAO FILHO, F. A. A. (2002).
Foliar micronutrient application effects on citrus fruit yield, soil
and leaf Zn concentrations and 65 Zn mobilization within the
plant. Acta Horticulturae, 594, 203–209.
BROWN,P.H.,ZHANG, Q. and BEEDE, B. (1994). Effect of foliar fertilization
on zinc nutritional status of pistachio trees. Annual
Report of the California Pistachio Industry, Crop Year 93–94.
Fresno, CA, USA. 77–80.
DEJONG,T. M., DAY,K.R.,DOYLE, J. F. and JOHNSON, R. S. (1994).The
Kearney Agricultural Center Perpendicular “V” (KAC-V)
orchard system for peaches and nectarines. HortTech, 4, 362–367.
E. E. SANCHEZ,S.A.WEINBAUM and R. S. JOHNSON
REFERENCES
843
several post-harvest foliar sprays would be required to
overcome severe Zn deficiency in peach trees. To fully
answer this question, additional research is needed to
determine the effect of multiple sprays, solutions of
different concentration, and times of application on the
efficiency of Zn uptake in mature bearing trees.
We conclude that foliar applications of Zn in the
Autumn are not very efficient at supplying Zn to peach
trees (< 10%), especially when compared to supplying N
as Autumn urea sprays (≥ 50%). However, once
absorbed by the tree, Zn is quite mobile and is stored
throughout the plant, including in the roots. During early
Spring growth, this stored Zn is supplied to new shoot
growth in greater percentages than N, especially for that
portion stored in the roots. Thus, the most significant
barrier to improving the efficiency of Zn fertilisation in
peach trees is getting adequate Zn into the tree, not its
mobility once it is in the tree. New approaches to
improve the efficiency of Zn uptake would be useful.
Ongoing research is required to determine the
quantitative significance of foliar applications of Zn,
which have become a standard practice for many peach
growers. Since sprays are often applied during leaf
senescence in late Autumn (Johnson and Uriu, 1989),
many leaves fall to the ground before any efflux of Zn
has occurred. Other leaves are induced to abscise within
1 – 2 weeks and may not have sufficient time to export
the full 7 – 8% of foliar-applied Zn that may be available
for export. Thus, there is a good chance that foliar
applications supply substantially less of the Zn needs of
growing fruits and shoots than we have estimated above.
Indeed, since at least 92 – 93% of the applied Zn falls to
the ground with senescing leaves, the greatest effect is
probably on increasing soil Zn levels (Boaretto et al.,
2002). This could increase the availability of Zn for root
uptake, but eventually could lead to problems with heavy
metal contamination of the soil.
The authors acknowledge the technical assistance of
Kevin Klassen and Becky Phene at the Kearney
Agricultural Center, and the Interdisciplinary Center of
Plasma Mass Spectrometry, specifically Michelle Gras
for her expertise in developing and implementing the
methodology for Zn isotope determination at UC Davis.
FERRANDON, M. and CHAMEL, A. R. (1988). Cuticular retention,
foliar absorption and translocation of Fe, Mn and Zn supplied
in organic and inorganic form. Journal of Plant Nutrition, 11,
247–263.
GARNETT, T. P. and GRAHAM, R. D. (2005). Distribution and remobilization
of iron and copper in wheat. Annals of Botany, 95,
817–826.
GRAUKE,L.J.,STOREY,J.B.,EMINO, E. R. and REED, D. W. (1982).
The influence of leaf surface, leaf age, and humidity on the
foliar absorption of zinc from two zinc sources by pecan.
HortScience, 17, 474.
HASLETT,B.S.,REID, R. J. and RENGEL, Z. (2001). Zinc mobility in
wheat: Uptake and distribution of zinc applied to leaves or
roots. Annals of Botany, 87, 379–386.
HAUCK, R. D. and BREMNER, J. M. (1976). Use of tracers for soil and
fertilizer research. Advances in Agronomy, 28, 219–266.

844
HIPPS, N. A. and DAVIS, M. J. (2001). Effects of foliar zinc applications
at different times in the growing season on tissue zinc concentrations,
fruit set, yield and grade out of culinary apple trees.
Acta Horticulturae, 564, 145–151.
JOHNSON, R. S. and URIU, K. (1989). Mineral Nutrition. In: Peaches,
Plums, and Nectarines, Growing and Handling for Fresh
Market. (LaRue, J. H. and Johnson, R. S., Eds.). University of
California Division of Agriculture and Natural Resources,
Publication 3331. 68–81.
KADMAN,A. and LAHAV, E. (1978). Experiments with zinc supply to
avocado trees. In: Proceedings of the 8th International.
Colloqium of Plant Analysis and Fertilizer Problems. (Ferguson,
A. R., Bieleski, R. L. and Ferguson, I. B., Eds.). New Zealand
DSIR Information Series 134, Government Printer,Wellington,
New Zealand. 225–230.
LONGNECKER, N. E. and ROBSON, A. D. (1993). Distribution and
transport of zinc in plants. In: Proceedings of the International
Symposium of Zinc in Soils and Plants. September 27-28. Perth,
Western Australia. 79–91.
MILLARD, P. (1996). Ecophysiology of the internal cycling of nitrogen
for tree growth. Journal of Plant Nutrition and Soil Science,
159, 1–10.
MILLIKAN, C.R.,HANGER, B. C. and BJARNASON, E. N. (1969). The
mobility of 65 Zn in Trifolium subterraneum L. and Antirrhinum
majus L. Australian Journal of Biological Science, 22, 311–320.
NEILSEN, G. H. and NEILSEN, D. (1994). Tree fruit zinc nutrition. In:
Tree Fruit Nutrition. (Peterson, A. B. and Stevens, R. G. Eds.).
Good Fruit Grower, Yakima, WA, USA. 85–93.
ORPHANOS, P. I. (1975). Spray application of zinc to young apple
trees. Horticulture Research, 15, 23–30.
PAGE, V. and FELLER, U. (2005). Selective transport of zinc, manganese,
nickel, cobalt and cadmium in the root system and
transfer to the leaves in young wheat plants. Annals of Botany,
96, 425–434.
ROSECRANCE,R.C.,JOHNSON, R. S. and WEINBAUM, S.A. (1998).The
effect of timing of post-harvest foliar urea sprays on nitrogen
absorption and partitioning in peach and nectarine trees.
Journal of Horticultural Science & Biotechnology, 73, 856–861.
SÁNCHEZ, E. E. and RIGHETTI, T. L. (2002). Misleading zinc deficiency
diagnosis in pome fruit and inappropriate use of foliar
zinc sprays. Acta Horticulturae, 594, 363–368.
Foliar application of labelled N and Zn in peach
SÁNCHEZ, E. E., RIGHETTI, T. L., SUGAR, D. and LOMBARD, P.B.
(1992). Effects of timing of nitrogen application on nitrogen
partitioning between vegetative, reproductive and structural
components of mature ‘Comice’ pears. Journal of Horticultural
Science, 67, 51–58.
SWIETLIK, D. (1999). Zinc nutrition in horticultural crops.
Horticultural Reviews, 23, 109–178.
SWIETLIK, D. (2002a). Zinc nutrition of fruit crops. HortTechnology,
12, 45–50.
SWIETLIK, D. (2002b). Zinc nutrition of fruit trees by foliar sprays.
Acta Horticulturae, 594, 123–129.
SWIETLIK, D. and FAUST, M. (1984). Foliar nutrition of fruit crops.
Horticultural Reviews, 6, 287–355.
SWIETLIK, D. and ZHANG, L. (1994). Critical zinc 2+ activities for
sour orange determined with chelator-buffered nutrient solutions.
Journal of the American Society for Horticultural Science,
119, 693–701.
TAGLIAVINI, M., MILLARD, P. and QUARTIERI, M. (1998). Storage of
foliar-absorbed nitrogen and remobilization for spring growth
in young nectarine (Prunus persica var. nectarina) trees. Tree
Physiology, 18, 203–207.
TOSELLI, M., THALHEIMER, M. and TAGLIAVINI, M. (2004). Leaf
uptake and subsequent partitioning of urea-N as affected by
the concentration and volume of spray solution and by the
shoot leaf position in apple (Malus domestica) trees. Journal
of Horticultural Science & Biotechnology, 79, 97–100.
VOLSCHENK, C.G.,HUNTER, J. J., LEROUX, D. J. and WATTS, J.E.
(1999). Effect of graft combination and position of application
on assimilation and translocation of zinc in grapevines. Journal
of Plant Nutrition, 22, 115–119.
WEINBAUM, S. A. (1988). Foliar nutrition in fruit trees. In: Plant
Growth and Leaf-Applied Chemicals. (Neumann, P.E., Ed.).
CRC Press Inc., Boca Raton, FL, USA, 81–100.
ZHANG, Q. and BROWN, P. H. (1999). Distribution and transport of
foliar applied zinc in pistachio. Journal of the American Society
for Horticultural Science, 124, 433–436.
ZIEGLER, E. E., SERFASS, R. E., NELSON, S. E., FIGUEROA-COLON, R.,
EDWARDS, B.B.,HOUK, R.S. and THOMPSON, J. J. (1989). Effect
of low zinc intake on absorption and excretion of zinc by infants
studied with 70 Zn as extrinsic tag. Journal of Nutrition, 119,
1647–1653.