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Seasonal variation in yield fruit quality and nutritional status of greenhouse tomato under different fertilization management plans
Kavvadias V.1 *, Daggas T.2, Paschalidis Chr.3, and E. Vavoulidou1
1 NAGREF, Soil Science Institute of Athens, 1 Sof. Venizelou Str, 141 23, Lycovrisi, Attiki, Greece.
2 Natural Balance, Fruits and Vegetables, Stavrodromi Gianitsa, Greece.
3 Technological Education Institute of Kalamata, 241 00 Antikalamos, Messinia, Greece.
* Address correspondence to: Victor Kavvadias, N.AG.RE.F., Soil Science Institute of Athens, 1 Sof. Venizelou Str, 141 23, Lycovrisi, Attica, Greece. E-mail: email@example.com, firstname.lastname@example.org, Tel: +30 210 2816974, Fax: +30 210 2842129.
Abstract: A study was conducted in the region of Pella, Stavrodromi, North Greece for two consecutive years. The work investigated the effect of various fertilization plans at various growth stages on the vegetative growth, yield, fruit quality and nutritional status of a greenhouse semi long life tomato cv “Formula”. It was found that the recommended fertilization plan (a combination of application of NPK fertilizers until harvest) gave the highest yields (104 and 137 t ha-1 at 1st and 2nd year of experimentation respectively) when compared to other treatments (different combinations of N and calcium (Ca) applied to soil at week intervals until harvest). Soil application of Ca at different week intervals until harvest had no substantial effect in greenhouse tomato. It was concluded that the recommended NPK fertilization in combination with application of K during harvest could be the basis for an effective nutrient management in greenhouse tomatoes established on areas with similar soil climatic conditions.
Key words: Calcium, fertilization, nitrogen, tomato, quality.
Tomatoes (Lycopersicon esculentum L.) belong to the category of fruits with high consumption worldwide. In the Mediterranean region, where continuous cropping is a common practice, plastic-covered greenhouse tomato cultivation is a major economic activity. Greenhouse tomato production constitutes one of the most important farming practices in Greece. According to FAO (2009), 1.5 million tons of tomatoes were produced in Greece in 2007. Tomato is reported to be a heavy feeder of NPK (Balliu and Ibro, 2002; Hebbar et al., 2004). Excessive use of nitrogen (N) fertilizers during cultivation of greenhouse tomato, adversely affects plant growth, fruitset, fruit color, greenhouse ventilation and it promotes late yields and heterogeneity in production. Moreover the nutritional imbalances from excessive N fertilization reduce the defense mechanism of the plant and encourage attacks by pathogens (eg. Phytophthora infestans, Botrytis cinerea) (Malathrakis and Kilronomou, 1992). Calcium (Ca) plays an important role in the nutrient uptake by tomato plants (Mengel and Kirkby, 1982). However its relative immobility in conjunction with high N doses and adverse environmental conditions prevailing in greenhouses, could negatively affect nutrition and growth of tomato plants and it can be the cause for blossom end rot (Saure, 2001).
Therefore sustainable practices are needed to maintain high tomato yields and improve fruit quality. There have been many studies on fertilization in open field vegetable cropping systems, but little information exists on fertilizer requirements in greenhouse tomato cultivation and particularly in Greece, where there is a lack of appropriate fertilization management plans. The aim of this work was to study the growth and the nutritional status of greenhouse tomato typically grown in the region of Pella, North Greece, in relation to N and Ca fertilization.
MATERIALS AND METHODS
A two year study was conducted in the region of Stavrodromi, prefecture of Pella, Central Macedonia, Greece, where there is extensive greenhouse tomato cultivation. Soils of the region are classified as Entisols xerofluvents according to USDA classification (Soil Survey Staff, 1999). Tomatoes are mainly grown as the first crop during spring and it can also be grown as a second crop during summer-fall. The experiment was established according to common Greek agricultural techniques under the Integrated Management System. Farmers use technologies and ICM practices for the production and development of high quality products following EUREP GAP, and AGRO 2-1 & AGRO 2-2 (www.agrocert.gr).
The aim of the work was to investigate the effect of various fertilization plans, (Table 1) on the growth, yield, and nutritional status of a greenhouse semi long life tomato hybrid cv. “Formula”. Fertilization plans included: 1. Control: only basal P, K and Mg fertilization, 2. NPK fertilization based on a) soil analysis results, and b) fertilization recommendations according to local agricultural cooperative and a consultant service company based on knowledge and experience gained in the long term cultivation of tomato (fert1) and 3. Combinations of NPK fertilization and soil CaO application (fert2-fert8) (Table 1). The experiment was a totally randomized design with 9 treatments laid out in 4 experimental plots. Each experimental plot consisted of 64 tomato plants placed in four rows of 16 plants each. The plants of the outer rows and the two plants in each end of the middle row were kept as guard plants. Intra-row spacing was 33-35 cm and rows in each plot were set 1.20 m apart to approximate 25,000 plants ha-1. The experiment was conducted in a plastic greenhouse covered by UV + IR + antifog polyethylene, oriented in north-south direction, and 11 x 60 m in size. Relative humidity and air temperature ranged between 40-50% and 15-280C respectively during the day and between 70-90% and 12-140C during night respectively over the course of the study. No additional light was provided in the greenhouse. The greenhouse soil was a sandy loam (SL) with chemical characteristics presented in Table 2.
Semi long life tomato 25 days old seedlings were planted in a nursery on 15/2/04 and on 20/2/2005. The growth substrate was a mixture of stabilized manure, sand and soil in 1:1:1 ratio, free from pathogens since the mixture before use has been subjected to solarization. Seedlings remained in nursery for 43-45 days, where all the necessary cultivation practices were applied. Healthy and uniform plants were transplanted in the greenhouse on 30/3/04 and on 8/4/05.
Soil Sampling: Before planting, 10 samples from a depth of 0-30 cm were collected and mixed in one sample.
Basal fertilization: Basal fertilizers were applied in all greenhouse treatment plots 30 days before the transplanting. Based on the results of soil analysis, 50 kg P2O5/ha, 140 kg K2O/ha, and 50 kg MgO/ha were applied as superphospate (0-20-0), potassium sulfate (0-0-50) and magnesium sulfate (16% MgO) respectively. The fertilizers were surface broadcast by hand and were then thoroughly incorporated into the top 30 cm of soil by milling machine.
Fertilization in treatments Fert2-Fert8: In treatments Fert2-Fert8 each plant received the appropriate doses of fertilizers dissolved in one litter of water. Nitrogen in treatments Fert2-7, was applied in the form of ammonium nitrate. Levels of K and P in treatments Fert2-8 were the same as that in treatment Fert1 and were given in the form of sulfuric acid and potassium sulfate respectively. Calcium was applied in the form of CaO.
Irrigation and cultivation techniques: Water was applied with a trickle irrigation system composed of distribution lines with drip tubes placed at the base of each plant, each with a flow rate of 2 l h-1. As the plants grew, all lateral shoots were removed manually, and the resulting single stem was trained up a string according to the high wire system. The oldest leaves, those at the bottom of the stem, were periodically removed.
Plant tissue sampling: Samples were taken from 24 uniform plants in each replicate. The third youngest fully expanded leaf from the top of each plant and one fruit from the truss under harvest were collected for nutrient analysis. Samples of leaves and fruits were collected at the beginning and at the end of each harvest period. Harvest started when plants had developed the 6th truss with a duration from 20/5 to 12/7 and from 7/6 to 15/7 in the first (2004) and second year (2005), respectively. Sampling of leaves took place on 30/5/04 and 2/7/04 and on 10/6/05 and 12/7/05 for year 1 and 2 respectively and that of fruits on 17/6/04 and 10/7/04 and on 10/6/05 and 12/7/05 for years 1 and 2 respectively. Tomatoes were harvested every 4-5 days at the early red stage (stages 7–8 according to the KleurStadia, Holland, tomato color chart) on an individual fruit basis.
Measurements at harvest: During harvest the following measurements were taken for each plant in each treatment and replication: Total fruit yield (a), fruit weight (b), number of fruits (c), number of trusses (d), as well as Botrytis incidence of fruits (percentage of fruits per plant) (e) and number flowers was recorded.
Chemical analysis: The chemical analyses of soil and plant samples were done according to the methods suggested by SSSA, (1990).
Soil analysis: The following properties of the soil were determined: Electrical conductivity (E.C), pH (paste), carbonates by using Bernard calcimeter, organic matter was determined by dichromate oxidation, available P by sodium hydrogen carbonate (1M NaHCO3 pH 8.5) extraction, exchangeable K by extraction with IN NH4Ac pH 7.0, and available Zn, Fe, and Mn extracted by DTPA and measured with an atomic absorption spectrophotometer (Perkin Elmer AAnalyst 100 Atomic Absorption Spectrometer). Soil B was extracted with 0.02 M CaCl2 and it was measured by the azomethine-H procedure (Wolf, 1974) using a HITACHI U-2910 Spectrophotometer.
Plant analysis: Tissues (leaves and fruits) were first cleaned with washing powder, then washed with tap water and finally with distilled water. The samples were dried in the oven at 70 0C until constant weight and ground to pass through a mesh screen to achieve sample homogeneity before mineral concentration analysis. Leaf and fruit samples were analyzed for total Ν, P, Κ, Ca, Mg, and Na. Total N was determined by Kjeldhal method. Prior to the measuring of the other nutrients, tissue samples were subjected to dry ashing at 5200C for 5 h and then were diluted with HCl in a 1:1 ratio v/v. Phosphorus was determined by the vanadomolybdophosphoric yellow colour method. Potassium, Ca, Mg, and Na in digests were measured by using a Perkin-Elmer A-100 atomic absorption spectrophotometer. Nitrates were determined with a colorimetric method developed by according to Cataldo et al., (1975) using a HITACHI U-2910 Spectrophotometer.
Statistical analysis: Data were evaluated by using analysis of variance (ANOVA). Treatment means were separated by using Duncan Multiple Range Test (P < 0.05). A correlation analysis was also conducted to determine the relations among different variables.
RESULTS AND DISCUSSION
Yield, vegetative parameters and Botrytis incidence: Tomato plants gave higher yields in second year of experimentation for all treatments (Fig. 1) mainly due to high yields achieved at the end of the harvesting period (Fig. 2). This could be attributed to the differences in growth under different weather conditions. At the end of harvest period in the second year, outdoor temperatures raised to 37-390 C which may have increased tomato root and shoot growth and therefore fruit yield. Increased temperature can increase tomato fruit yield, biomass (Teasdale and Abdul-Baki, 1995) and root growth (McMichael and Burke, 1998). Moreover the occurrence of frost in the first year might have reduced yields. The recommended fertilization plan without application of Ca (Fert1) gave the highest yields (104 and 137 t ha-1 in Year 1 and 2 respectively) which were significantly higher in Year 2. Greenhouse soil (table 2) contained adequate to high nutrient concentrations the first year of the experiment, perhaps the cause of no yield difference. Tomato plants in treatment Fert1 gave high yields for longer period during the harvesting stage of year 1 in relation to the other treatments (Fig. 2). Therefore under normal greenhouse conditions this can be an advantage for harvesting plans of greenhouse tomatoes and their market distribution. The highest tomato yields obtained in fert1 can be attributed to the significantly higher number of trusses per plant and fruits per plant (Table 3). Moreover plants grown in this treatment showed enhanced resistance to Botrytis cinerea compared to most of the treatments. Although synthetic chemicals are used extensively to manage B. cinerea (Gullino, 1992), control is often difficult and incomplete. Thus, our fertilization plan could reinforce the effectiveness of B. cinerea control in greenhouse tomato. The least affected plants were those receiving only calcium and that may be related to the physiological role of the element and to low nitrate content obtained in fruits (Tzamos, 2004; Agrios 2005).
Soil application of Ca did not affect tomato yield. Hadi et al., (1996) have shown that high Ca supply can even reduce shoot, fruit growth and yield. Demand for higher Ca supply at rapid growth may not exist since at this stage high membrane permeability is required for solute flux (Marschner 1995, Saure 2001). Fertilization with a double dose of N did not promote high yields due to the fact that high doses of N produce many fruits but relatively lower weight fruits (Panagiotopoulos, 1995).
Nutrient concentration: The levels of nutrients, except K, of the different treatments were within the ranges that allow a suitable development of the tomato crop. Plants did not show any visual deficiency or toxicity symptoms. More specifically the following were found: Concentration (dry weight basis) of N in fruits (Table 4) and leaves (Table 5) was decreased during the period of harvest and ranged from 2.79%-3.49% in 1st sampling to 2.60%-3.12% in the second sampling while that in fruits was reduced from 1.75%-2.45% in 1st sampling to 1.70%-2.10%. Fertilization treatments significantly affected fruit and leaf N concentration at the start of harvest but not at the end. Levels of N were higher in the treatment with a double dose of N (Fert3) and lower in the control. Time of soil Ca application was negatively related to fruit P and positively to leaf P at the first sampling while no consistent differences were obtained at the end of harvest. Application of Ca at the third, fifth and eighth week of cultivation (Fert 8), gave fruits with lower nitrate concentration in comparison with other nitrogenous treatments and particularly those where Ca was given at the end of the harvest. This could be due to alkaline environment of the root zone promoted by Ca application. These results are directly connected with human health since NO3 is considered to be carcinogenic and also a cause of methemoglobinemia (Craddock, 1983).
Calcium, due to its immobility, was accumulated in leaves at the end of the harvest period and ranged from 0.90%-2.41% in 1st sampling to 3.86%-6.21% in the second sampling while that in fruits was reduced from 0.23-0.35% to 0.19-0.31%. Concentration of Ca in tomato fruits during their development is reduced due to the reduction of fruit respiration, while that of K and Mg increases (Xillogiannis, 2004). Soil application of Ca (Fert4-Fert8) did not cause any significant differentiation in plant Ca concentration in relation to the other treatments. Application of soil Ca at the beginning of the cultivation period (fert 4) favors the accumulation of Ca and the other nutrients (K, Mg) in plant tissues, which may positively affect tomato quality. There was an indication that Ca concentration in fruits was stimulated by the recommended fertilization indicating a suitable fertilization practice in order to alleviate the reduction of Ca in fruits, which subsequently affects the fruit quality. Fruit Ca significantly correlated with yield (r=0.53, P=0.05 and r=0.77, P=0.01 in first and second sampling respectively) which suggested that an increase of Ca could stimulate fruit growth and yield. The foliar application of Ca until the harvesting stage for Ca nutrition of greenhouse tomatoes should also be considered.
In contrast with Ca, K markedly decreased in leaves during harvest (from 2.50-3.60 % in 1st sampling to 1.47-1.83 % in second one), while it increased slightly in fruits. Treatment effect was significant only on nutrient concentration of leaves in the initial sampling. Potassium ions are characterized by high mobility in long-distance transport via the xylem and phloem. Therefore, plant organs preferentially supplied with phloem sap (young leaves, fleshy fruits) are replenished in this nutrient (Marschner, 1995). Considering the ease with which this nutrient is translocated, it is reasonable not to find significant differences in plant K. Despite the adequate soil K levels (table 2) the concentrations of K in leaves were below the recommended values for optimum growth of tomatoes (Koukoulakis, 1994). Soil exchangeable K has been shown to inadequately predict tomato K status and fruit yield response to soil K application (Hartz et al., 2002) partly related to the growth characteristics of the tomato cultivars. The inadequacy of K in the plant combined with the fact that tomato cultivation has been established on light texture soils with alkaline pH indicate that despite the basal fertilization given in the beginning of the experiment, additional K fertilizer may be required to realize the full yield potential of tomato under the current experimental conditions. In addition K is considered to be the key to production of quality fruits (Marschner, 1995). Studies on open-field and greenhouse tomato crops (Williams and Kafkafi, 1998; Chapagain and Wiesman, 2004) showed that the supply of K at specific growth stages of the tomato plant would improve fruit quality. The demand for K fertilization indicated by the significant positive correlations between fruit K and yield (r=0.54, P=0.05). Therefore K fertilization can be continued until the end of harvest preventing the fruit contents of K from declining to low levels in order to promote yield and quality of tomato fruits.
Magnesium, like Ca, was markedly accumulated in leaves during harvest ranging from 0.49-1.06 % in the 1st sampling, to 1.58-2.47 % in the second one but this trend was not so evident in fruits. Treatments had little effect on fruit Mg concentration. Sodium was also accumulated in leaves during harvest from 0.37%-0.55% at the beginning to 0.41%-0.72% at the end of harvest. Differences between samplings were not clear in fruits.
The findings of this study help to improve the quality of tomato fruits, reduce the use of N-fertilizers and thus NO3 emission to the environment as well as reduce the cultivation costs of greenhouse tomato. High tomato yields with low incidence of Botrytis cinerea on fruits can be achieved by a fertilization plan where low amounts of fertilizers and particular N are applied and basal fertilization did not include N dressings. Tomato yields showed a significant response to the recommended NPK fertilization (Fert2) which in combination with application of K during harvest could be the basis for an effective nutrient management in greenhouse tomatoes established on areas with similar soil and climatic conditions. Moreover, this study has shown that, under the current experimental conditions, soil application of Ca at different week intervals until harvest has no substantial effect in greenhouse tomato. However, this study also realizes the need of further investigation about the interaction of foliar Ca application in greenhouse tomato.