The quality of the tomatoes is a complex concept and includes the appearance, value and biological value of fruit (Boteva, 2009; Mitova, etc.,2010; Atanasova et al.,2009). In the implementation of the programme for harmonization in March 2002, the Collegium of Ministry of Agriculture and Food adopted Decree No 9 for
Requirements for quality and control of the fresh fruit and vegetables (edu. DV, # 42/24.04.2002). In 2012 in conjunction with European subsidies (art. 68, regulation-73 from 2009), the Ordinance was enriched with additions. The Ordinance relating to the control of the quality, however, treats only morfometričnite indicators for quality of fresh fruit and vegetables. For the commercial market appearance is essential for the supply of output, but for full and healthy feeding of consumer biological or nutritional value of the proposed product is the most important. Formation of quality production of tomatoes is a function of the variety, the agrotehnika and soil-climatic conditions. Balanced fertilisation is an important factor in controlling rastežnite and reproductive events. In this context, particular emphasis is given to potassium. The potassium is an indispensable element for all living organisms (Nikolova, 2010; Rajkova, 1977; Mengel and Kirkby, 1981). Potassium fertilisation is a major, rapid-factor for improving the quality of most field (soil) and substrate grown vegetables.
Purpose of the study was to determine the impact of increasing rates of potassium on certain morphological and biochemical parameters characterizing the quality of varieties and hybrids determinant tomatoes, grown as early field production.
Material and methods
The experiment was carried out on the cinnamonic-podzolic (pseudopodzolic) soil in the field station of N.Poushkarov Institute in Primorsko, district of Burgas, in 2009-2010 . The soil is characterized with high humic content- 2,3%, medium soil acidity- pH 5.0, low content of mineral nitrogen (NH4-N-7.2 mg/kg; N03-N-3, 7mg/kg), available phosphorus-3,3 mg/100 g and average content of K20-15,3 mg/100 g. The experiments started in the middle of May with planting of seedlings. Block method with the size of the test plot 9,6 m2 in 4 replications was used. The first fruits are taken on the 15 July. Harvests have been made during the 7 days.
Four cultivars of tomato were used. All of them are included in the official catalogue in Bulgaria- Trapezitsa, Elena F1, Nikolina F1 and Dora (Mitova, 2007). Four levels of potassium (K0. K80, K160 and K240 kg. ha-1) and equal nitrogen and phosphor fertilizations as background were combined. The potassium is imported in the form of potassium chloride, nitrogen as ammonium nitrate, and phosphorus as
double superphosphate. Variants of the trial are shown in table 1. For convenience when considering results of variants in the trial will be shown with the initials of the variety, with a capital letter and potassium dose as an index to the right. Bio-chimical indicators for quality of fruit were determinated between the first and fourth yeilds.
After taking into account the yield of fruit in phase “marketing maturity” are sampled for analysis. The samples were pre-treated for chemical analysis after drying at 60oC with preliminary fixation (at 105oC). The content of total sugars wasdetermined refractometrically in (%) (by Digital refractometer-32-145). the content of nitrates and ascorbic acid was determined on the apparatus RQ flex plus 10 of Merck).
Results and discussion
Influence of potasssium applied on morfometric indicators for quality of production
The biomass of fruit from the second harvest are included as morfometric indicators (table 1).
Table 1. Impact of K-fertilization and variety on the weight of fruits , kg/ha
|Trapezitza||Elena F1||Nikolina F1||
|LSD at 5%||270,28||264,92||311,16||459,78|
The yields from cultivated in the study tomato varieties are representative indicators. Parallel changes forl varieties and hybrids tomatoes between fertiliser and the mass of the collected fruit were shown. The varieties of tomato expressed some specifics. While Trapezitsa (174,6 g/fruit) and Nikolina F1 (256,97 g/fruit) at-large from fertilisation by K16 rate, then when Elena F1 under the most high fertiliser rate-K24. was obtained and a maximum weight of the fruit (258,77 g/fruit). In variety, Dora will statistically proven differences between the two latest versions (295 87 g/fruit when applied with N200P180K160 and 300,43 g/fruit in N200P180K240). To control variant, toren with N200P180K0, the mass of the various varieties grow between 8.07
and 26,46% for variety Trapezitsa; 7,23% at variety-45,78 Elena F1; 14,19-35,51% at variety Nikolina F1 and 9,48-24,03% in variety Dora. Increasing potassium standards will have a major impact on the accumulation of mass of variety Elena F1 between 7,23 and 45,78% relative to the control. The largest mass of fruit in the experiment is the variety Dora due as of potassium manure, so probably and varieties characteristics. The average mass of the fruit is 81,1% greater than that of variety Trapezitsa, with 30,83% of variety Elena F1 and with 21,45% than that of variety Nikolina F1.
Influence of potassium on the biochemical parameters of quality
Nitrate content is an important characteristic of quality and food safety of vegetables. Having in mind former knowledge that species of tomatoes as a rule do not accumulate nitrates in red fruit (Mitova and Dinev, 1995) in this test and in the two analysis of mature fruits of tomato expressed low content of nitrates in experimental variants. A number of studies (Bamouh et al., 2010; Mengel and Kirkby, 1982) demonstrates the impact of potassium fertilization on the accumulation of dry matter in fruit of tomatoes in field and in glass-house. Cited in the literature limit values for the index move in widely-from 3,3 to 7,8%, and depend on many factors (Nikolova, 2010; Rajkova, 1977). Noticed that the values of absolutely dry substance (ADS) in the earlier phase of reporting are noticeably more low, than later. In the first harvest ADS in the experience varies between 2,86 and 3,6%, and the second between 4,10 and 6,12%. In both harvest there has been a trend for increasing the dry matter increase of potassium rate. High values in control variants of some of the varieties, are due to «the effect of dilution», which is derived from an earlier completion of the vegetal stages in these plants because of poor conditions for development. While early harvest varieties Nikolina F1 and Dora most high values of dry matter is high in potassium, and norm in Trapezitsa and Elena F1 for fertilisation by K160, then in the later harvest high potassium application rate of K240 provided the greatest accumulation of dry matter in all varieties.
Well known is the role of potassium in the movement of assimilates in the conductive vessels of plants, together with activation synthesis of dry matter shall be increased and synthesis of reduced and total sugars, is the intensity of breathing and increases the accumulation of vitamin «c» as a product of the oxidizing processes when breathing (Rajkova, 1977;. Mengel and Kirkby, 1982). Yet Brezhnev (in 1964). has established, that with increasing rates of potassium fertilizer sugars in fruits increased by 25 to 35%. The content of total sugars in the experience with tomatoes and two yields running in approximately the same borders-between 3.3 and 6,3%. In the early harvest with the exception of the control variants, in which the same explanation as for dry substance at all test varieties with growth of potassium dose is the sugar content. In the later harvest in the case of varieties of Elena F1 and Dora trend is maintained, while in Trapezitsa and Nikolina F1 data are ambiguous. In all varieties in both plants with yields fertilized K24 gained the most common sugars, as with most high content of sugars from both yields is variety Trapezitsa-6,3%. As average indicator, however, only at the first harvest variety Trapezitsa is with most high content of total sugars (average of all variants of fertilization of the variety-5,0%). in later harvest variety Dora surpasses other varieties with on average content of sugars for variants of fertilization 5,13%.
Table 2. Impact of fertilization and variety on the biochemical properties of
|variant||Dry matter, %||Total||sugars,||Total||acidity,||Vit. C %|
The content of total acids is a dynamic indicator and is determined both by species and variety features and conditions of cultivation. Referred to in the literature data for acidification in the tomatoes (Mitova and Dinev, 1995; Mitova etc., 2005; Kancheva et al., 2005; Hartz et al., 1999) varied between 0.30 and 0.5%. Acidification in the outputted experience moves between 0.38 and 0.60% in both analyses of fruit. In four test varieties with the invasion of the growing the acidification decreases. With the high content of total acids in fruit variety is Dora in both yield-variant with application of K240-0.60% and averages of-0.5% in early and 0.56% in the later harvest.
The ratio of synthesized sugars to acidification in fruit of tomatoes is an important indicator characterizing the quality of outputs. In the literature (Rajkova, 1977) as an optimal indicated ratio 5,6-8.7. From the data presented in table 2 shows that, in most variants of the tested varieties that range is much wider, with the result that the resulting values significantly in excess of those referred to in the literature as optimal. With the lowest average for all variants, fertilizing value of indicators characterizing the ratio of total sugars/acids-9,08 is variety Elena F1, where in potassium application rate of 160 kg K/ha is calculated and the lowest value-8,14.
The content of vitamin C (ascorbic acid) is an extremely important indicator for tomatoes, determining their nutritional and dietetic characteristic. In publications indicate a wide range (19,53-30,16 mg%) in the content of vitamin C, which is
determined by the many and varied factors such as production direction, the agrotechnique, varietal characteristics (Brezhnev, 1964; Mitova and Dinev, 2011; Bamouh et al., 2010; Yagmur et al., 2004). A special place is given to the role of potassium feeding of plants on the synthesis of vitamin C. However, in the literature indicate that the content of Ascorbic acid in the earlier harvesting of tomatoes is less, the average content of Ascorbic acid by all variants of the outputted experience in both harvesting is approximately equally: 16,38 mg% in first and 16,21 mg% in next. In the first harvest plants of all varieties, fertilized with K240 have most high content of vitamin c, and in the next, this trend is clearly demonstrated in the variety only Dora. In both analysis of fruit variety Dora have shown the most high levels of ascorbic acid, on average 22,7 mg% of first and 23,3 mg% of second harvest. In both readings variant fertilized with K24 is with most high levels of vitamin c in fruit-25.5 mg% in first and 26,0 mg% in next measurement.
- Increasing potassium rate have a major impact on the accumulation of mass of variety Elena F1 between 7,23 and 45,78% relative to the control. The largest mass of fruit in the outputted experience is the variety Dora due as of potassium fertilization and varietal characteristics. The average mass of the fruit is 81,1% greater than that of variety Trapezitsa, with 30,83% of variety Elena F1 and with 21,45% than that of variety Nikolina F1.
- At two harvestings there has been a trend for increasing the dry matter increase of potassium rate. While early harvest varieties Nikolina F1 and Dora most high values of dry matter is high in potassium, and norm in Trapezitsa and Elena F1 for fertilization by K160, then in the later harvest high potassium application rate of K240 provided the greatest accumulation of dry matter in all varieties.
- In all varieties in both plants with harvests with K240 gained the most common sugars, as with most high content of sugars from both harvests is variety Trapezitsa-6,3%. As average indicator, however, only at the first harvest variety Trapezitsa is with most high content of total sugars (average of all variants of fertilization of the variety-5,0%). in later harvest variety Dora surpasses other varieties with on average content of sugars for variants of fertilization 5,13%.
- The four tested varieties with the invasion of the vegetation acidification decreases. With the high content of total acids in fruit variety is Dora in both harvests-variant with fertilized K24-0.60% and averages of-0.5% in early and 0.56% in the later harvest
- With the lowest average for all variants, fertilizing value of indicators characterizing the ratio of total sugars/acids-9,08 is variety Elena F1, where in potassium application rate of 160 kgK/ha is calculated and the lowest value-8,14.
- In both analysis of fruit variety Dora have shown the most high levels of ascorbic acid, on average 22,7 mg% of first and 23,3 mg% of second harvest. In both readings variant fertilized with K24 is with most high levels of vitamin c in fruit-25.5 mg% in first and 26,0 mg% in next measurement.
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