Effect of Nutri-Vant-PeaK foliar spray on plant development, yield, and fruit quality in greenhouse tomatoes

 
Scientia Horticulturae 102 (2004) 177–188

      Effect of Nutri-Vant-PeaK foliar spray on plant
               development, yield, and fruit
              quality in greenhouse tomatoes
                               B.P. Chapagain, Z. Wiesman∗
      Bio-Industry Laboratory, The Institutes for Applied Research, Ben-Gurion University of the Negev,
                                  P.O. Box 653, Beer-Sheva 84105, Israel
                                          Accepted 2 December 2003

Abstract

   Fruit development in tomato is often accompanied by the depletion of foliar potassium to the
detriment of both the plant and the fruit quality. In an attempt to restore high foliar levels of potassium
in the greenhouse tomato Lycopersicon esculentum Mill cv. Durinta, the leaves were sprayed with
Nutri-Vant-PeaK, a novel foliar nutritive formulation based on monopotassium phosphate (MKP)
and designed to provide controlled and lasting penetration of potassium and phosphorus into leaves.
Nutri-Vant-PeaK contains 95% MKP and 5% Ferti-Vant, a non-destructive and long-lasting adjuvant
delivery system. The findings were compared with those for plants sprayed with MPK. The two types
of foliar fertilizer were administered at 1% (w/v) concentrations on days 40, 70 and 100 after planting.
Nonsprayed plants served as the controls. Plant height, leaf chlorophyll and mineral contents, and
fruit maturity were monitored during plant development. Total and marketable yields and fruit number
and size distribution were measured after the harvest. Fruit appearance and quality were scored
following cold storage under conditions simulating export. Plants sprayed with Nutri-Vant-PeaK
were taller than the plants in the other two groups. Chlorophyll, potassium, phosphate, magnesium
and iron contents in the leaves were significantly higher in plants sprayed with Nutri-Vant-PeaK or
MKP than in nonsprayed plants. Fruit matured significantly earlier in plants sprayed with MKP or
Nutri-Vant-PeaK. Marketable yield was significantly higher in the Nutri-Vant-PeaK treatment group
than in the other two groups. Fruit quality of plants spray with Nutri-Vant-PeaK was superior: there
was a higher percentage of firm fruit and a lower percentage of blotchiness and rotten fruits than
in the control plants. Glucose content and dry matter after storage were higher for fruit from both
groups of sprayed plants than for control plants, whereas fruit potassium, phosphorus and magnesium
contents were higher only for the Nutri-Vant-PeaK group. Fruit total nitrogen, nitrate, calcium, iron and
zinc contents were not affected by the spraying treatments. The results clearly show that application

 ∗ Corresponding author. Tel.: +972-8-6477184; fax: +972-8-6477184.
E-mail address: wiesman@bgumail.bgu.ac.il (Z. Wiesman).

0304-4238/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.scienta.2003.12.010
178               B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188

of foliar potassium and phosphorus nutrition via Nutri-Vant-PeaK is beneficial for greenhouse tomato
production.
© 2004 Elsevier B.V. All rights reserved.

Keywords: Tomato; Foliar spray; MKP; Nutri-Vant-PeaK; Fruit quality; Fertigation

1. Introduction

    Tomato (Lycopersicon esculentum Mill) is one of the most widely consumed vegetable
crops in the world, with an estimated 99.4 million t of tomatoes being produced worldwide
each year (FAO, 2002). Since the tomato plays an important role in human health, the quality
of the nutritional components of this major crop fruit of particular concern to producers
throughout the world.
    Among the factors that influence the quality of tomato, potassium plays a key role, since
it is involved in metabolic processes, such as the synthesis of proteins, enzyme activation,
membrane transport processes, charge balance, and the generation of turgor pressure (Dorais
et al., 2001). As the tomato plant grows, the absorption of potassium increases to a relatively
greater extent than that of other nutrients (Voogt and Sonneveld, 1997). When potassium
uptake is lower than demand, foliar potassium is mobilized to the fruit, to the detriment
of plant growth and fruit set and quality (Besford and Maw, 1975; Mengel and Kirkby,
1987). Since the tomato fruit contains large concentrations of potassium, fruit development
imposes considerable demands for this mineral, and depletion of foliar potassium is a
common occurrence (Williams and Kafkafi, 1998).
    Although the required amount of potassium can be supplied to greenhouse tomatoes
through the fertigation system, we surmised—on the basis of studies on fruit trees and
open-field tomato crops (Uriu et al., 1980; Lavon et al., 1996; Williams and Kafkafi,
1998)—that a foliar supply of potassium at specific growth stages of the tomato plant
would improve fruit quality. The major problems associated with foliar application of fer-
tilizers, particularly to annual plants (Swietlik and Faust, 1984)—the cuticular barrier and
leaf burn—can be overcome by using low-salt-index fertilizers (i.e. those free of Na and Cl)
containing a low concentration of potassium and an appropriate adjuvant (Weinbaum, 1988).
    Among the potassium and phosphate fertilizers used in foliar application, MKP (mono-
potassium phosphate, PeaK® ; 52% P2 O5 , 34% K2 O) is the formulation with the lowest salt
index and is thus the foliar fertilizer of choice for many crops (Ankorion, 1998). However,
there is some disagreement about whether spraying with this fertilizer causes scorching of
the foliage. Some studies have suggested that the horticultural product PeaK is almost as safe
as analytical MKP for hydroponics and foliar sprays (Neumann and Etzion, 1993; Ankorion,
1998), and another study has shown that repeated spraying of field-grown tomatoes with a
3% solution of MKP did not cause visible damage and improved both yield and fruit quality
(Williams and Kafkafi, 1998). It has also been reported that foliar spraying of citrus trees
with PeaK increased total soluble solids (TSS), phosphate and potassium and decreased
nitrate concentration in the fruit and enhanced the yield (Lavon et al., 1996). Similarly, our
previous studies showed that a foliar spray of 2% MKP increased the yield and fruit quality
of greenhouse tomatoes despite leaf burn (Chapagain, 2001). These results encouraged us
B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188     179

to seek methods that would facilitate a reduction in the dose of MKP in the foliar spray
while retaining the positive effects of the fertilizer on greenhouse tomatoes.
   A new foliar nutritive product recently developed in our laboratory is currently being
marketed under the name Nutri-Vant-PeaK. This product consists of MKP crystals (95%)
coated with 5% of a novel non-destructive adjuvant delivery system known as Ferti-Vant
(Agro-Vant Ltd., Israel) that regulates the rate of nutrient penetration through the foliar
cuticular membrane and promotes sustained absorption of nutrients (Wiesman et al., 2002a).
The Ferti-Vant-based system significantly reduces the risk of leaf and fruit burn in many
plant species and also enhances yields and other horticultural parameters (Wiesman et al.,
2002b).
   The aim of the present study was to test the effects of foliar spraying of Nutri-Vant-PeaK
on plant development, fruit yield and quality, and time to fruit maturity in greenhouse
tomatoes. Plants sprayed with Nutri-Vant-PeaK were compared with those sprayed with
non-coated MKP, the common foliar fertilizer, and with unsprayed plants in a controlled
fertigated greenhouse tomato system.

2. Materials and methods

   The study was carried out from October 2000 to March 2001 on tomato plants cv. Durinta
growing in a greenhouse on the grounds of the Institutes for Applied Research, Ben-Gurion
University of the Negev, Beer-Sheva, Israel. In winter, the greenhouse was heated at night
to maintain a minimum temperature of 11 ◦ C. During the course of the study, monthly
minimum temperatures were 11–16 ◦ C, and maximum temperatures ranged from 29 to
33 ◦ C. The experimental system consisted of a randomized complete design, replicated
four times in groups of eight plants per replicate (total of 32 plants per treatment).
   Seedlings were planted in Perlite, an inert growth medium, in 10 l plastic pots on 20 Oc-
tober 2000. Plants were spaced at 0.4 m in paired rows, with 1 m between the rows, giving
a total of approximately 25,000 plants ha−1 . At 40, 70, and 100 days after planting (DAP),
1% concentrations (w/v) of PeaK® (Rotem Amfert Negev, Israel) or Nutri-Vant-PeaK
(Agro-Vant Ltd., Israel) were sprayed on the leaves of the plants comprising the two treat-
ment groups. The control plants were not sprayed. All plants (treatment and control groups)
were fertigated with a solution containing 180 mg l−1 of K and 50 mg l−1 of P (average
concentration). Each plant thus received approximately 54,000 mg of K and 15,000 mg of P
(average 2 l per day per plant) during the 150-day experiment. MKP-sprayed plants received
1.4% (749 mg) of K and 4.1% (693 mg) of P (average 100 ml per spray per plant × 3 sprays)
more than the control plants, and the plants sprayed with Nutri-Vant-PeaK received 95%
of the amounts of K and P applied to MKP-sprayed plants. Spraying was performed by
the conventional “run-off” method with a power-operated back-pack sprayer (Vermoreal,
France).
   Fertigation was supplied to each pot via a single dripper with a 2 l h−1 discharge rate. The
leaching fraction was in the range of about half of irrigation. Heading back of the plants
was performed at 136 DAP, and harvesting began at 95 DAP. Fruits were harvested every
other day only from trusses 1 to 5 at the early red stage (stages 7–8 according to the Kleur
Stadia, Holland, tomato color chart) on an individual fruit basis.
180             B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188

   Plant height, leaf chlorophyll and mineral contents, and fruit development were evaluated
during plant growth. Total yield, marketable yield and fruit number, along with fruit size
distribution and weight, were determined at harvest as described previously (Chapagain
et al., 2003). Fruits having a diameter of less than 47 mm as well as diseased and off-type
fruits were considered as unmarketable. After harvest, selected fruits were kept in storage (at
12 ◦ C for 12 days and 20 ◦ C for 3 days) to simulate export conditions (Chapagain, 2001).
Fruit quality parameters (firmness, dry matter (DM), number of rotten or blotchy fruits
(blotchiness), calyx status, juice electrical conductivity (EC), pH, TSS, glucose, titratable
acidity (TA) and mineral contents) were analyzed after the simulated storage as described
by Chapagain et al. (2003).
   Young fully expanded leaves (five and six from the top) were picked and washed thor-
oughly with de-ionized distilled water to remove any contamination from the leaf surface
prior to extraction and oven drying at 70 ◦ C for 72 h. Thereafter, the leaves were ground
for determinations of leaf nutrients. For the fruit nutrient analyses, 10 samples of eight
fruits per sample (two samples from each of trusses 1–5) from the stored fruits were se-
lected, and slices of the individual fruits of each sample (including pericarp, seeds and
jelly) were oven dried at 70 ◦ C for 72 h and subsequently ground. Each fruit was washed
well with de-ionized distilled water before grinding to remove any external contamination.
Contents of P, K, Ca, Mg, Fe, Mn, B, Zn and Na in leaves and fruits were analyzed by
ICP-AES (Perkin-Elmer OPTIMA-3000) following acid digestion. N was determined by
the macro-Kjeldahl method, and Cl by titration with 0.5N AgNO3 .
   Homogenized fruit tissue was centrifuged (14,000 rpm, 10 min), and the following pa-
rameters were determined in the supernatant: EC by means of an EC Meter (TH 2400,
EL-Hana Instruments, Israel), pH by means of a pH Meter (EcoMet P15, MRC, Israel),
TSS by means of a digital refractometer (PR-100, ATAGO, Japan), TA by titration with
NaOH (0.05N), glucose by means of an Elite Glucometer (Bayer, UK), and NO3 by means
the Reflectoquant nitrate test (MERCK-Rqflexz). Leaf chlorophyll was determined as de-
scribed by Moran (1982).
   Statistical analysis of the data was performed with JMP software (SAS, 2000) using
the Tukey–Kramer HSD test for determining significant differences among treatments at
P = 0.05.

3. Results

3.1. Plant growth and leaf analysis

3.1.1. Plant height
   The height of the tomato plants was measured on four different dates: 39 DAP (before
first spray), 69 DAP (1 month after the first spray, i.e. just before the second spray), 99 DAP
(1 month after the second spray, i.e. just before the third spray), and 130 DAP (1 month after
the third spray). There were no significant differences in plant height at 39 DAP. At 69 DAP
plants sprayed with MKP or Nutri-Vant-PeaK were significantly taller than the control
nonsprayed plants, whereas at 99 and 130 DAP only those sprayed with Nutri-Vant-PeaK
were significantly taller than the control plants (Table 1).
B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188             181

Table 1
Effect of foliar spray of MKP and Nutri-Vant-PeaK on the height of tomato plants
Treatment                      Plant height (cm)

                               39 DAP                  69 DAP                99 DAP              130 DAP

Control                        70.85 a                 158.85 b              218.71 b            270.32 b
MKP                            71.23 a                 163.18 a              222.23 ab           271.56 ab
Nutri-Vant-PeaK                71.11 a                 164.23 a              225.56 a            282.41 a
1% MKP or Nutri-Vant-PeaK was sprayed at 40, 70, and 100 days after planting (DAP). Values are means for 32
plants. Means in each column followed by different letters are significantly different at P ≤ 0.05.

3.1.2. Leaf chlorophyll content
   Leaf chlorophyll content was determined at 15, 45, 75, 105, and 135 DAP. At 15 and
45 DAP, there were no significant differences in chlorophyll a and chlorophyll b contents
among the three groups of plants (Table 2). At 75 and 105 DAP, however, levels of chloro-
phylls a and b were significantly higher in the two groups of sprayed plants. At 135 DAP,
levels of both chlorophylls a and b were significantly higher in the plants sprayed with
Nutri-Vant-PeaK than in the MKP-sprayed and nonsprayed plants.

3.1.3. Leaf mineral composition
   Leaf mineral composition was analyzed six times during the experiment: before the first
spray (39 DAP), 1 week after the first spray (46 DAP), before the second spray (69 DAP), 1
week after the second spray (76 DAP), before the third spray (99 DAP), and 1 week after the
third spray (106 DAP). At 39 DAP, no significant differences in leaf minerals were evident
among the three treatment groups (Table 3). At 46 DAP, leaf K content was significantly
higher in the two groups of sprayed plants as than in the control plants, and leaf P, Mg, Fe
and Ca were slightly, but not significantly, higher in the sprayed plants. At 69 DAP, the leaf
K content of the plants sprayed with Nutri-Vant-PeaK was significantly higher than that of
the control plants and MPK. At 76 DAP, not only leaf K but also P and Fe contents were

Table 2
Effect of foliar sprays of MKP and Nutri-Vant-PeaK on chlorophyll contents of tomato leaves
Treatment                    Leaf chlorophyll content (␮g cm−2 )

                             15 DAP           45 DAP               75 DAP          105 DAP        135 DAP

Chlorophyll a
  Control                    14.12 a          16.59 a              16.89 b         17.46 b        18.46 c
  MKP                        14.43 a          16.35 a              17.42 a         19.38 a        19.20 b
  Nutri-Vant-PeaK            13.86 a          16.32 a              17.52 a         19.56 a        20.23 a
Chlorophyll b
  Control                    5.16 a           6.08 a               6.92 b          6.87 b         6.87 c
  MKP                        5.03 a           6.10 a               7.69 a          7.68 a         7.29 b
  Nutri-Vant-PeaK            5.26 a           6.14 a               7.88 a          7.87 a         7.79 a
1% MKP and Nutri-Vant-PeaK was sprayed at 40, 70, and 100 days after planting (DAP). Values are means for
32 samples. Means in each column followed by different letters are significantly different at P ≤ 0.05.
182                B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188

Table 3
Effect of foliar sprays of MKP and Nutri-Vant-PeaK on mineral composition of tomato leaves
Treatment                   Leaf mineral composition (mg g−1 dry matter)

                            P              K                Ca               Mg              Fe

39 DAP (before first spray)
  Control                   9.25 a         42.52 a          15.97 a          8.84 a          0.14 a
  MKP                       9.41 a         42.49 a          15.72 a          8.76 a          0.14 a
  Nutri-Vant-PeaK           9.31 a         42.93 a          15.23 a          8.96 a          0.14 a
46 DAP (1 week after first spray)
  Control                    9.12 a        42.65 b          15.33 a          8.82 a          0.14 a
  MKP                        9.56 a        43.95 a          15.67 a          9.05 a          0.15 a
  Nutri-Vant-PeaK            9.40 a        44.54 a          15.89 a          9.12 a          0.16 a
69 DAP (before second spray)
  Control                  8.48 a          37.32 b          14.35 a          7.96 a          0.11 a
  MKP                      8.65 a          39.21 b          14.23 a          8.02 a          0.12 a
  Nutri-Vant-PeaK          8.98 a          42.95 a          14.41 a          8.11 a          0.14 a
76 DAP (1 week after second spray)
  Control                  8.43 b          37.03 b          14.25 a          7.91 a          0.11 b
  MKP                      9.12 a          40.52 a          14.65 a          8.21 a          0.13 a
  Nutri-Vant-PeaK          9.23 a          41.24 a          14.85 a          8.32 a          0.14 a
99 DAP (before third spray)
  Control                   7.23 b         31.56 b          15.20 a          7.53 b          0.12 b
  MKP                       7.46 b         34.87 b          15.56 a          7.76 ab         0.13 ab
  Nutri-Vant-PeaK           8.43 a         38.28 a          15.60 a          8.12 a          0.14 a
106 DAP (1 week after third spray)
  Control                   7.25 b         30.65 b          15.30 a          7.43 b          0.12 b
  MKP                       8.84 a         36.85 a          15.51 a          8.12 a          0.14 a
  Nutri-Vant-PeaK           8.89 a         40.12 a          15.60 a          8.31 a          0.15 a
1% Nutri-Vant-PeaK was sprayed at 40, 70, and 100 days after planting (DAP). Values are means for 32 samples.
Means in each column followed by different letters are significantly different at P ≤ 0.05.

significantly higher in both the MKP- and Nutri-Vant-PeaK-sprayed plants compared with
the control plants (Table 3). At 99 DAP, leaf P and K contents in the plants sprayed with
Nutri-Vant-PeaK were significantly higher than those in the other two groups. On this date,
the levels of leaf Mg and Fe for the MKP-treated plants fell between those of the control and
the Nutri-Vant-PeaK groups. At 106 DAP, leaf P, K, Mg and Fe were significantly higher
in both groups of sprayed plants than in control plants (Table 3). There were no significant
differences among the treatments for minor elements like Zn, Na, B, Cl and Mn (data not
shown).

3.2. Fruit growth and maturation

   The average time to anthesis (measured from DAP to anthesis of 50% of the flowers of a
cluster) did not differ significantly among the three groups (Table 4). For the first five trusses,
the time to harvest (planting to picking of 50% of the fruits of a cluster) was significantly
B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188               183

Table 4
Effect of foliar spray of MKP and Nutri-Vant-PeaK on time to anthesis, time to harvesting, and time to fruit
maturity of tomato
Treatments                     Truss

                               First            Second             Third            Fourth             Fifth

Time to anthesisa
                (days)
  Control                      24 a             35 a               43 a             53 a               62 a
  MKP                          24 a             35 a               43 a             50 a               59 a
  Nutri-Vant-PeaK              25 a             35 a               43 a             51 a               60 a
Time to harvestb (days)
  Control                      101 a            109 a              115 a            123 a              131 a
  MKP                           92 b            103 b              107 b            114 b              120 b
  Nutri-Vant-PeaK               94 b            104 b              109 b            115 b              123 b
Time to maturityc (days)
  Control                      77 a             74 a               72 a             70 a               69 a
  MKP                          68 b             68 b               64 b             64 b               61 b
  Nutri-Vant-PeaK              70 b             69 b               66 b             64 b               63 b
1% MKP and Nutri-Vant were sprayed at 40, 70, and 100 days after planting. Values are means for eight plants.
Means in each column followed by different letters are significantly different at P ≤ 0.05.
   a Time from planting to anthesis of 50% flowers of a cluster.
   b Time from planting to picking of 50% fruits of a cluster.
   c Time from anthesis to picking of 50% fruits of a cluster.

shorter (by more than 1 week) in both groups of sprayed plants than in control plants. Time
to maturity (anthesis to picking of 50% of the fruits of a cluster) was significantly shorter in
both MKP- and Nutri-Vant-PeaK-sprayed plants. In addition, plants of both sprayed groups
showed a pattern of progressively short maturity from truss 1 to 5. There were no significant
differences in maturity between MKP- and Nutri-Vant-PeaK-treated plants.

3.3. Yield and fruit quality

3.3.1. Fruit yield
   The percentage of small fruits was significantly lower in plants sprayed with Nutri-Vant-
PeaK than in control plants. The marketable yield was significantly higher for the plants
sprayed with Nutri-Vant-PeaK even though there were no significant differences in total
yield and average number of fruits per plant among the three treatment groups (Table 5).
There were no significant differences in both total and marketable yields among the trusses
within all three treatment groups (data not shown).

3.3.2. Fruit appearance
   The percentage of rotten fruits in the Nutri-Vant-PeaK group was significantly lower
than that in the other two groups. The percentage of firm fruit was significantly higher and
blotchiness (blotchy fruits) significantly lower in the Nutri-Vant-PeaK group than in fruits
from the control plants. There were no significant differences in the percentages of fruits with
calyx or in calyx freshness after the storage simulation among the three groups (Table 6).
184                 B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188

Table 5
Effect of foliar sprays of MPK and Nutri-Vant-Peak on percentage of small fruits, total and marketable yields and
average number of fruits per plant of tomato
Treatments                  Small                  Total yield              Marketable               Average number of
                            fruitsa (%)            (g/plant)                yield (%)                fruits per plant
Control                     9.58 a                 3560 a                   87.59 b                  32.43 a
MKP                         8.48 ab                3580 a                   87.30 b                  32.65 a
Nutri-Vant-PeaK             7.35 b                 3640 a                   90.06 a                  33.16 a
1% MKP and Nutri-Vant were sprayed at 40, 70, and 100 days after planting. Values are means for fruits from 32
plants of trusses 1 to 5. Means in each column followed by different letters are significantly different at P ≤ 0.05.
    a Small fruits ≤ 47 mm diameter.

Table 6
Effect of foliar sprays of MKP and Nutri-Vant-PeaK on appearance of tomato fruits
Treatment                 Firm                Rotten              Fruits with            Calyx                 Blotchiness
                          fruits (%)          fruits (%)          calyx (%)              freshnessa            (%)
Control                   48.80 b             4.16 a              99.00 a                1.98 a                7.81 a
MKP                       52.23 ab            4.00 a              98.91 a                2.01 a                5.25 ab
Nutri-Vant-PeaK           58.00 a             2.60 b              98.87 a                2.48 a                3.22 b
1% MKP and Nutri-Vant-PeaK were sprayed at 40, 70, and 100 days after planting. The analysis was performed
after storage simulation (at 12 ◦ C for 12 days and 20 ◦ C for 3 days). Values are means for 20 samples (eight fruits
per sample) taken from trusses 1 to 5. Means in each column followed by different letters are significantly different
at P ≤ 0.05.
    a Calyx freshness: 1 = low; 2 = medium; 3 = high.

3.3.3. Fruit quality parameters
   Fruit glucose content was significantly higher in Nutri-Vant-PeaK-sprayed plants than
in fruit from the other two groups. Fruit TSS was significantly higher in Nutri-Vant-PeaK
sprayed plants than in control plants. The TSS of the MKP-sprayed plants was not signifi-
cantly different from the control plants or the Nutri-Vant-PeaK-sprayed plants. There were
no significant differences in juice pH, TA and EC among the treatments. DM of the fruit
was significantly higher for the two sprayed groups than for the control group (Table 7).

Table 7
Effect of foliar spray of MKP and Nutri-Vant-PeaK on tomato fruit quality parameters
Treatment              Fruit quality parameter

                       pH            Glucose           TSS             TA                         EC             DM (%)
                                     (mg g−1 FW)       (% Brix)        (meq g−1 FW)               (dS m−1 )
Control                4.21 a        7.09 b            3.51 b          0.06 a                     4.85 a         4.85 b
MKP                    4.08 a        7.10 b            3.71 ab         0.07 a                     4.84 a         5.00 a
Nutri-Vant-PeaK        4.22 a        7.81 a            3.92 a          0.07 a                     5.06 a         5.04 a
1% MKP and Nutri-Vant was sprayed at 40, 70, and 100 days after planting. The analysis was done after simulation
storage (at 12 ◦ C for 12 days and 20 ◦ C for 3 days). Values are means for 10 samples (eight fruits per sample) taken
from trusses 1 to 5. Means in each column followed by different letters are significantly different at P ≤ 0.05.
TSS: total soluble solids; TA: titratable acidity; EC: electrical conductivity; DM: dry matter.
B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188                      185

Table 8
Effect of foliar sprays of MKP and Nutri-Vant-PeaK on fruit mineral composition of tomato
Treatment            Fruit mineral composition (mg g−1 dry matter)

                     N (% DW)       NO3               P           K           Ca        Mg         Fe        Zn
                                    (mg g−1 FW)
Control              2.00 a         0.017 a           5.35 b      42.47 b     5.23 a    2.46 b     0.06 a    0.04 a
MKP                  2.00 a         0.013 a           5.98 ab     44.39 ab    5.46 a    2.65 a     0.06 a    0.05 a
Nutri-Vant-PeaK      1.96 a         0.014 a           6.44 a      48.30 a     5.64 a    2.64 a     0.06 a    0.05 a
1% MKP and Nutri-Vant-PeaK were sprayed at 40, 70, and 100 days after planting. The analysis was performed
after storage simulation (at 12 ◦ C for 12 days and 20 ◦ C for 3 days). Values are means of 10 samples (eight fruits
per sample) from truss 1 to 5. Means in each column followed by different letters are significantly different at
P ≤ 0.05.

There were no differences in these parameters between trusses within the treatment groups
(data not shown).

3.3.4. Fruit mineral composition
   Fruit Mg was significantly higher in the two sprayed treatment groups than in the control
plants, whereas K and P were higher only in the plants sprayed with Nutri-Vant-PeaK
(Table 8). Contents of N, NO3 , Ca, Fe and Zn were not significantly different among fruits
of the three groups (Table 8). Contents of other minor elements, such as Mn, Cl, B and Na,
did not differ significantly among the treatments (data not shown).

4. Discussion

   The main aim of this experiment was to investigate the effects of foliar application of
the new coated MKP product, Nutri-Vant-PeaK, on greenhouse tomatoes. The beneficial
effects of the product were evident from a preliminary study that showed an increase in plant
height, a decrease in the percentage of small fruits, and a significant increase in levels of
fruit glucose, TSS, and EC in comparison with the values for nonsprayed plants. However,
the results of the preliminary study also illustrated one of the known disadvantages of the
foliar spraying technique—leaf burn: some signs of burning were visible on the margins
of lower leaves two days after spraying with as low a concentration as 2% MKP, but these
moderate symptoms vanished as the plant matured, and no other detrimental effects were
noticed (Chapagain, 2001). It has previously been reported that 3% MKP is the highest
concentration that field-grown tomato foliage can tolerate without visible damage after
seven cumulative applications of MPK together with the surfactant L-77 (Williams and
Kafkafi, 1998). Our current experiment was therefore designed with the aim of balancing
the promotive effect of MPK with protection from leaf burn. To this end, the MKP was coated
with superior delivery system—Ferti-Vant (Wiesman et al., 2002a) and the concentration
of MPK was reduced to 1%.
   The results of the current experiment showed a significant initial increase in plant height
in both the MKP and Nutri-Vant-PeaK groups, but at the later stages of the experiment
plants were significantly taller only in Nutri-Vant-PeaK group (Table 1). A similar pattern
186             B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188

was evident for leaf chlorophyll content (Table 2). These findings indicate that “greenness”
and vigor increased with application of both MKP and Nutri-Vant-PeaK, but the promotive
effect was sustained only in the plants sprayed with Nutri-Vant-PeaK.
   The pattern repeated itself once again for contents of leaf minerals. In addition to increased
P and K contents, Mg and Fe contents rose during the later stages of plant growth in plants
sprayed with either MKP or Nutri-Vant-PeaK, but the levels of these minerals remained
higher only in the plants sprayed with Nutri-Vant-PeaK (Table 3). Although control plants
obtained adequate amounts of P (50 mg l−1 ) and K (180 mg l−1 ) via fertigation, the levels
of both these minerals declined (P 22% and K 28%) during fruit development, in keeping
with the results reported by Williams and Kafkafi (1998). In the sprayed plants, this decline
was much smaller (P 6% in MKP treatment; 4% in Nutri-Vant-PeaK treatment; K 13%
in MKP treatment; 6.5% in Nutri-Vant-PeaK treatment). Higher levels of leaf P and K in
response to spraying with MKP were also observed in Star Ruby grapefruit (Lavon et al.,
1996). As was the case for P and K, there was a 15.9% decline in the leaf Mg content of
the control plants, whereas the decline was only 6% in the sprayed plants. There was also a
drop in leaf Fe content in the control plants, but not in the sprayed plants. The decreases in
the P, K and Mg in the leaves were accompanied by increases of these elements in the fruit.
The smaller decrease of leaf P and K in sprayed plants suggests that foliar application of
MPK prevented depletion of leaf P and K. The high levels of Mg and Fe in the leaf tissue
of the sprayed plants versus the control plants cannot be directly attributed to the MPK
spray: instead, it is probably due to the strong sink provided by the more vigorous sprayed
leaves.
   A comparison among the three plant groups of time to anthesis and time to harvest
showed a significant difference only in the time to harvesting between the sprayed groups
and the control. However, a comparison between trusses within a treatment group did show
differences in both time to anthesis and time to harvesting (Table 4). The differences in time
to anthesis between trusses within a treatment does not provide us with information on the
effect of the spray on fruit maturity because in an indeterminate type of tomato like Durinta
flowering starts with the first truss and then proceeds to the second and so on. In addition,
anthesis of the most of the flowers occurred either before or just after the first spray. The
stimulatory effect of MPK on ripening, as reflected in the significantly shorter time to fruit
maturity (anthesis to picking of the fruits) in all the sprayed plants, may be attributed to
the P component of the spray. Indeed, several studies (Burnik-Tiefengarber et al., 1994;
Yamada and Martin, 1994; Goren et al., 1998) have clearly demonstrated the effect of P
salts on the maturation of olive and citrus fruits. Our results clearly suggest that spraying
of MKP with—uncoated or as Nutri-Vant-PeaK—could provide tomato growers with an
early crop.
   Blotchiness and rotting of fruits during storage are common problems that are encountered
in the tomato industry (Dorais et al., 2001). The lower percentage of both rotten and blotchy
fruits from the Nutri-Vant-PeaK-sprayed plants (Table 6), i.e. the improved fruit appearance,
represents an important potential economic benefit to growers, since healthy appearing fruit
with fresh calyxes are indices of paramount importance to consumers. The increase in yield
and the improvement in post-harvest quality parameters may be related to the spray’s success
in preventing the leaf contents of K and other mineral nutrients from declining to low levels
during fruit set (Williams and Kafkafi, 1998).
B.P. Chapagain, Z. Wiesman / Scientia Horticulturae 102 (2004) 177–188                 187

    Foliar application of 1% Nutri-Vant-PeaK significantly increased the values of three pa-
rameters influencing the taste of tomato fruit, glucose, TSS and DM (Table 7). Lavon et al.
(1996) reported similar findings for citrus sprayed with PeaK, although they used a higher
concentration of PeaK (3%) to overcome the greater resistance of citrus leaves to foliar fer-
tilizer. Despite the lower concentration of 1% used in our experiment—a concentration that
supplied only an additional 1% K and 4% P during the course of 150 days—the percentages
of P and K in the tomato leaves were much higher than those reported for the citrus leaves
(Lavon et al., 1997). These superior results for tomato may be due to the effectiveness of
the Ferti-Vant delivery system, which facilitates sustained absorption of the elements into
the leaves (Wiesman et al., 2002a).
    The findings that foliar spraying with Nutri-Vant-PeaK reduced fruit total N and NO3
contents (although not significantly) while significantly increasing fruit P, K and Mg con-
tents might be of considerable relevance to human health and nutrition. The source of the
significantly higher fruit P, K, and Mg concentrations may lie in the higher levels of these
minerals in the leaf tissue. The lower NO3 is as yet unexplained, and a study on this subject
is currently under way.
    From the grower’s perspective, foliar application of 1% Nutri-Vant-PeaK at the later
stages of tomato plant growth, especially during fruit set and development, appears to
improve fruit quality and benefit marketability considerably, with a minimal risk of foliage
damage. While foliar spraying increases the cost of cultivation, the difference in outlay is
negligible when set against potential economic benefits gained from improved fruit quality.

5. Conclusion

   The results of this study show conclusively that three sprays of 1% Nutri-Vant-PeaK in
conjunction with regular fertigation prevented the depletion of leaf P and K and accelerated
fruit maturation and improved fruit quality in greenhouse tomatoes.

Acknowledgements

   The authors thank Mr. Shabtai Cohen and Mr. Rami Golan for their technical help and
Mrs. Inez Mureinik for editing this manuscript. We would like to thank to all staffs of
the Phyto-Oleochemical Laboratory of the Institutes for Applied Research, Ben-Gurion
University of the Negev, Isreal for their assistance. This study was supported by the Dibner
Fund.

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