Nutritional assessment of potassium in tomato ( Lycopersicon esculentum Mill . ) by direct reading of fruit sap

Analysis of content made available to the plants and their relationship with what is present in plant tissue, are great alternative for proper handling of fertilizer, but the methods currently used, are expensive and require time. This study aimed to implement a new methodology for its determination and thus develop a correlation with the conventional method. It also evaluated the influence of the increase of K doses in production, plant development and relationship with the other nutrients. For the study we used two experiments with fertirrigated tomato having five different doses of potassium, grown in a greenhouse and analyzed according to the methodology developed. In the experiments were evaluated productivity, illuviated electrical conductivity and nutritional content in the fruit and leaf immediately above each bunch. Potassium was analyzed by conventional methodology and for comparison purposes. The values were submitted to polynomial regression analysis to the second degree and correlation. The results showed that increased potassium levels significantly influenced the productivity, illuviated electrical conductivity and K contents. After comparing the two methods was reached a relationship where reading by the conventional method is 20.085 times higher than the values presented by reading without digestion if the sap of the fruit and 9.6857 in the sap of the leaf petiole. The new methodology has proved capable of replacing the conventional of quick, cheap and effective form. Increased potassium levels had significantly influence in the illuviated electrical conductivity, productivity and nutritional content of the plant tissue.


INTRODUCTION
Potassium (K) is one of the most required nutrients by plants, being responsible for the stomatal opening, which is related to photosynthesis and, consequently, to the synthesis of photoassimilatedes, and act as an enzyme activator (Taiz and Zeiger, 2013).
In the case of tomato, K is the nutrient most required by the plant about 180 mg dm -3 (Almeida et al., 2015), mainly after the onset of the breeding season (Faquin, 2001), where this becomes important nutrient translocation of photoassimilates, especially for fruits, interfering in their sugar content and the synthesis of lycopene pigment (Marschner, 2011).
Given the difficulties encountered by the tomato production, such as low prices, high competition, pests and diseases, alternatives are necessary to increase profitability.The growing, in greenhouse, in substrates and fertigation become feasible to increase productivity and fruit quality.However, they are expensive techniques that rely on extensive attention and time.In the case of alert to the electrical conductivity of fertigation nutrient solution, and the content of each nutrient in accordance with the development of the plant.
Seeking to better monitor the development of plants and their nutrition, the evaluation of the nutrient content in leaves and fruits, compared with the levels available for absorption, can, especially in the case of fertirrigated crops, determine which nutrient should have his concentration managed to achieve better productivity (Braga, 2010).
There are some devices on the market that estimate the present potassium content in the plant by liquid extracted mainly from the petiole, but they are inaccurate and in some cases lead to greater errors than hits.The most feasible method for such determination is by further extraction of the leaf, which is dried, crushed and then digested with a nitric and perchloric acid solution based on the methodology developed by Bataglia et al. (1983).This method, although more accurate, demand more time, work and cost.Aiming to seek an alternative that enables the potassium reading in the plant in order to clarify its content quickly and cost effectively has been prepared for this work a direct reading of this nutrient, without going through any process of digestion, for only in the case of this element, there is no formation of molecular bonds within the plant, the remaining ionic form (Taiz and Zeiger, 2013), which is easy to read in a flame photometer.The aim was to determine the K content of fruit and leaves of tomato through direct reading without digestion, and so develop a correlation with the conventional method and also evaluate the influence of K levels in the production and development of the plant.

MATERIALS AND METHODS
First there was the study of the best method for extracting the sap of the fruit and tomato leaf.Fruits of different maturity stages were used beyond the leaves just above the bunches where these fruits were collected in order to reach the best way of extracting and her best dilution for direct reading in a flame photometer.
It was coming to the conclusion that the best method to be used would be to slightly squeeze the fruits cut in half to collect only their sap, which was collected in a test tube and then filtered, allowed to decant the tube itself, or collected for dilution and immediate analysis.Of the three extraction methods, the choice was the decanting tube as not different values of others and proved to be the most practical method.The dilution was determined after several attempts not to exceed the last photometer reading point (100 ppm).For extracting the petiole was required great pressure on it because of its consistency, in this case with the aid of pliers.For dilution, both the fruit and the petiole to the best approach was to collect the extract and 0.1 ml diluted in 19.9 ml of deionized water and subsequently performing the direct reading in a flame photometer.

Plant materials
For the analysis of K and the new methodology testing levels, we used two experiments conducted in a greenhouse, arch type, with 6 m wide, 30 m long, 3 m high and transparent polyethylene cover, the Department of agronomy, and the samples analyzed in the Soil Laboratory, both from the State University of Londrina, Londrina city, State of Paraná, Brazil (latitude 23° 23'S, 51° 10'W longitude, at an altitude of 580 m).
These experiments consisted of K rate of increase in tests with two varieties of fertirrigated tomato grown in pots with sand, being in a randomized block design with five treatments and 10 repetitions, totaling 50 vases side by side and 60 cm between rows, with borders around and fertirrigated drip.
The seedlings were tomato type Pizzadoro for the experiment 1 (E1) and Carina to experiment 2 (E2), from certified commercial vivarium, which were transplanted to pots with 25-30 cm high, on 23 March 2013.The experiment was conducted until July 29 of that year.
The pest control was performed preventively and the following insecticides were applied from the start of cultivation: Cypermethrin (pyrethroid), 1 ml L -1 , every 15 days, large fruit borer (Helicoverpa zea) and Dipel® (biological) 1 ml g -1 once a week for tomato leafminer (Tuta absoluta).The fungicides applied from the reproductive stage were: Chlorothalonil, 5 ml L -1 once a week for early blight, septoria and powdery mildew and Amistar Top®, 1 ml L -1 once every 15 days also to early blight.

Fertirrigation system
The experiments were conducted with five treatments consisted of five concentrations of K in the nutrient solution (60,120,180,240 and 300 mg dm -3 of K) applied after the opening of the first flowers, with 29 days after transplanting, and until that stage of development, the nutrient solution was standard (180 mg dm -3 of K) for all treatments.These doses were established from prior knowledge of the mean dose of K which is recommended for the tomato crop, it would be 180 mg dm-3 (Almeida et al., 2015).From this information, it was decided to test doses, starting at 60 to 300 mg dm -3 .
Monitoring the concentration of each nutrient present it was given by periodically measuring the electrical conductivity of the solution Table 1.Nutrient Concentration (mg dm -3) and electrical conductivity (EC) (dS m -1 ) of the nutrient solutions used in the treatments.
in water tanks and the resulting illuviated the nutrient solution that passed through the vase and was retained on the plate below it, leaving the system conductivity exceed three dS m -1 which could adversely affect plant development.When the conductivity exceeded the three dS m -1 the fertirrigation was interrupted and the system was irrigated for one day only with water to prevent salinization of the system.
The fertigation system consisted of submersible pumps, with an operating pressure of up to 1.9 of metres of water column (mwc) and power of 38 watts, model AT 203 Atman® in water tank with 80 L capacity for each treatment.The pumps were connected to a timer, driven by a contactor to avoid damage due to oscillation of the amperage.The fertilizer applications were made through irrigation water with variable frequency so that the losses did not exceed 10% by irrigation interval, each dripper was set for maximum flow of 300 ml min -1 .The irrigation interval was defined based on climatic conditions how temperature, relative humidity, which were measured inside the greenhouse during the experiment, with datalogger Instrutherm® ht-500 model and the characteristics of culture, ranging from 1 to 5 times a day shift.
Average monthly temperatures were 33.6°C on 27 to 31 March 26°C in April, 27.5°C in May, 23.8°C in June and 27.9°C until the day July 29.The relative humidity was 42% of 27 to 31 March, 64.4% in April, 57% in May, 72.6% in June and 54.1% until July 29.Plants were conducted with three tomato bunches, and after the third bunch counted five leaves and pruned plants to cut the apical dominance.

Sample preparation treatments
After the onset of fruiting was collected a green fruit each repetition, the basal part of the bunch, with a diameter between four and five centimeters.It was also collected the leaf just above the same bunch for analysis, according to the experiment conducted by Almeida et al. (2015).It was determined the mass, diameter, length of the fruit and leaf mass collected over three clusters, each fruit was subsequently cut in half with one half its sap extracted as developed methodology.The leaves collected just above the three clusters had their sap extracted for direct analysis and then were analyzed by conventional methodology.
The other half of the fruit and leaf were placed in appropriately labeled Kraft paper bags and brought to air forced circulation stove at 65°C for three days.After drying was determined the dry weight of leaves and fruits and then crushed in Willey type mill.At the end of the experiments were obtained productivities and all plant material collected was prepared for determination of K by flame photometry for the final results.

Statistical analysis
The final results could be compared by means of polynomial regression to the second degree with 5% significance level, to establish a relationship between the two methodologies.The results of the different levels of K read from the sap of the petiole and fruits with and without digestion provided, as well as productivity and other nutrient levels have been correlated by Pearson correlation to determine which nutritional parameters the new methodology can measure, directly or indirectly.

Productivity
In regard to yield the highest value found in the two experiments was at a dose of 300 mg dm -3 K, with 80.00 t ha -1 at Experiment 1(E1) and 98.20 t ha -1 at Experiment 2(E2) (Table 2), agreeing with Sara et al. ( 2007) also observed an increase in the fresh weight production according to the concentration of nutrients until it reaches a saturation point where the output decreases considerably.Cook and Sander (1991) also observed a significant increase in tomato yield with the increase in the K doses, according to the results of E2 that had linear adjustment as increasing doses.However, E1 had a quadratic adjustment with the trend towards greater productivity for  ) in nutrient solution.ns: not significant data for 5% by regression analysis.
the dose of 180 mg dm-3 (76,23 t ha -1 ) agreement with Coltman and Riede (1992) who obtained similar results working with fertigation under greenhouse conditions with K five levels, with higher productivity at a dose of 200 mg dm-3.The total yield obtained in this experiment was similar to the 97.9 t ha -1 recorded by Macedo (2005).According to Fontes et al. (2000), the commercial and total yield of tomato have increased with the increase in the K doses, reaching a maximum of 73.4 and 86.4 t ha -1 , with the application of 194 and 198 kg ha-1 K respectively.Roquejani et al. (2008), in their studies with productivity and quality of tomato hybrids Italian segments and holy cross in the greenhouse when thinned, had an average yield of 106.7 t ha -1 to variety Giuliana.
The increased productivity observed in both experiments shows that when the tomatoes is conducted in the nutrient solution, where all nutrients are supplied in optimum quantity for their full development, increasing the amount of potassium, which is the nutrient required in greater quantity reflects directly in the best plant development and higher fruit production.

Illuviated electric conductivity
The means of illuviated electric conductivity (EC) in each dose of K differ significantly with increasing linear fit to the experiments (Table 3), the largest of which EC was obtained at a dose 300 mg dm -3 (3.46 dS m -1 to E1 and 3.14 dS m -1 for the E2) and the lowest was observed with 120 mg dm -3 K (2.28 dS m -1 ) in E1 and 60 mg dm -3 with K (2.49 dS m -1 ) to E2.
The results for the two experiments agree with Genúncio et al. (2006), working with growth and tomato yield under hydroponics in ionic concentration of the nutrient solution, where they observed values greater than 2.0 dS m -1 in the EC.
According to Maas and Hoffman (1977), the maximum tolerable soil salinity, expressed in terms of EC, the tomato is 2.5 dS m -1 , with a reduction of 9.9% in the production unit for each incremented EC.Eloi et al. (2007), testing effect of salinity in tomato grown in sandy loam soil, found the salinity threshold value of 3.03 dS m-1, very close to that seen in E1 and E2, with decreased productivity in 10.95% for each increase of one unit of soil salinity, caused by fertilizer salts.During the conduct of experiments care was taken not to allow the illuviated electric conductivity exceed 3.0 dS m -1 , so there was not salinity problems of the system, thus contributing to the full development of the plants.

Comparison of the two methods
After analysis of the K content in both methods of reading, in the sap of the fruit without digestion (SFWD) and K content in the dry matter of fruit with digestion (FRD), the three bunches of two experiments, it is concluded that there was significant difference with increased K content.There was an increase in K content (Tables 4 and 5) to the fruits of the second and third bunch without digestion in the E1 and E2 of the three bunches.The K levels after digestion had difference for the second and third lock of E1 and E2 in all bunches.
As the treatments had concurrent with beginning to flourish, it is appropriate to no significance to the first bunch in E1 for the plants are subject to treatments for a very short period.The results agree with the Blanco and Folegatti (2008), who worked with K levels in tomato hybrid "Facundo" under salt stress, and found that the higher the dose of K, the greater the absorption by fruit, Table 4. K content in g kg -1 of sap fruit without digestion (SFWD) and fruit with digestion (FRD) in the first.second and third bunch in accordance with increasing doses of potassium experiment 1. ) in nutrient solution.ns: not significant data for 5% by regression analysis.

K in g kg
Table 5.K content in g kg -1 of sap fruit without digestion (SFWD) and fruit with digestion (FRD) in the first.second and third bunch in accordance with increasing doses of potassium experiment 2. and found that the highest concentration was 35 g kg -1 , the highest dose applied (24 g plant-1 K).A suitable potassium fertilizer provides tomatoes with more pronounced red color and well formed inside, without the presence of voids.The fruits are firmly stuck in plants, reducing losses by fall.Disability, the fruits have bad coloration and shorter conservation.The excess may result in cracking in fruit (Moraes, 2006).

K em g kg
After comparing the two methods, direct reading from the sap of the fruit and reading after digestion of dry matter through polynomial regression to the second degree, it reached a relationship where reading with digestion, which is the conventional method used in laboratories, is 20.085 times higher than the values presented for reading without prior digestion, namely y=20,085x, where y is the value obtained by reading the sample after passing for digestion is the value obtained without prior digestion, as shown in Figure 1.As the levels found in the sap of the leaf petiole (SLP) and digestion of leaf (LD) collected directly above each bunch also had a significant response with increasing dose for the two methods (Tables 6 and 7).
The results shown in Tables 6 and 7 agree with Calvert (1969) found that increased K content in leaf tissue according to increasing doses of adult citrus plants and Miller et al. (1993) found that the same effect of increasing doses of rootstock citrus in the early stages of growth.Fertilizers with K promote increased concentration in plant tissue, as observed results in Tables 4, 5, 6, and 7, result in superior whole plant due to increased photosynthetic efficiency, resistance to certain diseases.In tomato, as K increases the concentration of the nutrient solution, the concentration of K in the leaf and fruit, as well as the amounts extracted by the same also increase.
The K is absorbed by the roots in the form of ion, the roots being translocated through mass flow to the outer membranes of the cells of the leaves and then stored in Table 6.K content in g kg -1 in the sap of the leaf petiole without digestion (SLP) and in the leaf with digestion (LD) just above the first.second and third bunches in accordance with the increase of K doses of experiment 1.  -3 ) in nutrient solution.ns: not significant data for 5% by regression analysis.the vacuole.When required for the tomato plant growth, it is transferred to the phloem and then mobilized to parties in growth as immature leaves and fruits (Wood and Parish, 2003).

K in g kg
The concentration of nutrients in the petiole sap indicates the amount of this circulating in the plant at the time and so the present levels both in the plant as being absorbed.The analysis of the sap, for diagnostic purposes, seeks to determine, in real time, the momentary concentration of K in the plant or NO3, and usually has a significant correlation with the concentration found in the leaf determined by the conventional method and the plant production, such as checked Alcantar et al. (2002) for the garlic crop.
After comparing the two methods by polynomial regression to the second degree was reached a relationship where reading with digestion, which is the conventional method used in laboratories, is 9.6857 times Table 7. K content in g kg -1 in the sap of the leaf petiole without digestion (SLP) and in the leaf with digestion (LD) just above the first.second and third bunches in accordance with the increase of K doses of experiment 2.  higher than the figures given for reading without digestion that is, y=9,6857x, where y is the value obtained by reading the sample after undergoing digestion exo value obtained without prior digestion, as shown in Figure 2. Moreira and Vidigal (2009) found relationship between NO3 content in the fourth potato leaf petiole sap with increasing doses of N. For K close relationship between its content in the sap of the petiole and leaf dry weight were reported by Qian et al. (1995) for the culture of canola and Kallenbach (2000) for alfalfa, agreeing with the observed in this study.

K in g kg
The K values obtained by both the methodology for direct reading without digestion, as the methodology with digestion could be compared using regression and correlation to find a relationship between the methodologies and nutritional aspects of the two varieties of tomato.Comparing the K in the sap of the petiole and leaf nutritional index, which in this study was considered just above the second cluster (Table 8) and the Convention as K values being obtained by reading with digestion, in tomaterio E1 Pizzadoro we came to a positive correlation of 0.924 (Figure 3A) and significant relationship verified through regression.For Carina conducted in tomato E2, also we had significant positive results by regression and correlation of 0.967 as shown in Figure 3B.
For variety Pizzadoro E1 compared by means of regression, the K content in fruit (Tables 4 and 5) without prior digestion with the content in the sap of the petiole (Tables 6 and 7), also without digestion was obtained a CV 33.62% with 5% significance and a correlation of 0.977, according to 3C.
The variety Carina E2 showed similar behavior when comparing the same parameters, where he met significance by regression analysis between K in the sap of the fruit without digestion and petiole of the leaves, also for reading without digestion.Was met a CV of 25.89% and correlation of 0.98 as a 3D figure.
The relationship between the K content found in the sap fruit without digestion with the leaf above its respective bunch, again reveals significant values for both experiments with positive correlation for the 0.885 tomato Pizzadoro (E1) (Figure 3E) and for the 0.903 tomato Carina (E2) (Figure 3F).When compared to the K content in the sap of the leaf petiole with the tomato have significant results for the two experiments, when subjected to regression of 0.375 and a positive correlation for E1 (Figure 3G) and 0.996 to E2 (Figure 3H).
The production compared with the K content in the leaves is significant in the regression analysis for the two varieties used, having a positive correlation of 0.113 in E1 (Figure 3I) and 0.983 in E2 (Figure 3J).When comparing the K content in the fruit after digestion with the production correlation found was positive 0.431 (Figure 3K) and no significant results after regression analysis for E1 and 0.981 positive and significant correlation values after regression analysis of E2 (Figure 3L).This fact is mainly the difference between varieties, where the Pizzadoro tomato (E1) had an increase in its output until the dose of 180 mg dm -3 of K and then a beginning of competition for nutrients and a decrease in productivity tend.
Already variety Carina (E2) responded better to increased K levels with significant results in production until the dose of 300 mg dm -3 , showing the behavior of each variety with respect to increasing doses and its response in production as can be seen in Figure 3K and  L. According to the results presented above with the correlations between: the K content in the sap of the fruit without digestion with the content in the petiole sap, the sap of the petiole and the nutritional leaf index, the sap without digestion fruit and leaves, sap petiole and the production and ultimately production and leaves, we can observe the close relationship between potassium uptake with increasing doses and their interaction with production.From the results it gives importance to the quadratic increase in production for the E1 and E2 linear for showing the influence of genotype on the absorption of nutrients and nutritional requirement as verified by Singh et al. (2000), Youssef et al. (2001), Ravinder-Singh et al. (1999) and Warner et al. (2004).About correlations can be said that the higher the K content in the leaf, the E and F Relationship between potassium levels found in the sap of the fruit without digestion and dry matter of the leaves in the experiments 1 and 2. G and H Relationship between potassium levels found in the petiole sap without digestion with production in experiments 1 and 2. I and J-Relationship between K concentration found in the leaf with production in t ha -1 for the experiments 1 and 2. K and G-Ratio between potassium levels found in fruit with production in t ha -1 in the experiments 1 and 2.

Figure 1 .
Figure 1.Regression between the readings of the K content in the sap of fruit without digestion and fruit after digestion for both experiments in the fruits of the three bunches.According to five levels of K.

Figure 2 .
Figure 2. Regression between readings with and without digestion for the two experiments on leaves in the three bunches.According to five levels of K.

Figure 3 .
Figure 3.A and B-Levels of potassium found in the sap of the petiole and nutritional leaf index of experiments 1 and 2. C and D-Potassium Levels found in the sap of the fruit without digestion and in the petiole sap from leaves without digestion of experiments 1 and 2.E and F Relationship between potassium levels found in the sap of the fruit without digestion and dry matter of the leaves in the experiments 1 and 2. G and H Relationship between potassium levels found in the petiole sap without digestion with production in experiments 1 and 2. I and J-Relationship between K concentration found in the leaf with production in t ha -1 for the experiments 1 and 2. K and G-Ratio between potassium levels found in fruit with production in t ha -1 in the experiments 1 and 2.

3 ) and of the nutritive solution conductivities ***
Sarruge (1975))modified and used in the UEL Soils Laboratory.** Nutrient solution used for 15 days for adaptation of seedlings.***Means of electrical conductivity (EC) measured in the nutrient solution water tanks (dS m -1

Table 2 .
Average of production in t ha -1 in function of K doses in both experiments.Significant data to 5% by regression analysis.ns: not significant data for 5% by regression analysis. *:

Table 3 .
Means of electrical conductivities of the two experiments in five treatments in dS m -1 .

Table 8 .
Macronutrient in g kg-1 in index leaf of the first and second experiment.collected just above the second bunch.
*: Significant data to 5% by regression analysis.ns: not significant data for 5% by regression analysis.