Effect of Nutri-Vant-PeaK foliar spray on plant development, yield, and fruit quality in greenhouse tomatoes
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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: email@example.com (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. References Ankorion, J., 1998. MKP (monopotassium phosphate) for foliar fertilization. In: El-Fouly, M.M., Abdalla, F.E., Abdel-Maguid, A.A. (Eds.), Proceedings of the Symposium on Foliar Fertilization: A Technique to Improve Production and Decrease Pollution, Cairo, Egypt, 10–14 December 1995, NRC, pp. 71–84. Besford, R.T., Maw, G.A., 1975. Effects of potassium nutrition on tomato plant growth and fruit development. Plant Sci. 42, 395–412.
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