Foliar application of Tecnokel Amino Zn had not a significant effect on the qualitative and quantitative parameters of corncob. Used preparation positively affected sugar content and the ear of maize size while carotenoids were not negatively affected. The influence of the variety was statistically significant.

An experiment was founded in 2016 in Botanical Garden of Slovak University of Agriculture (below BG SUA) in the field conditions. Area is situated in very warm agro-climatic region, very dry sub-region. The mean annual temperature was 10 °C (Table 1) with average annual rainfalls 62.4 mm per month (Table 2). Meteorological measurements were carried out by the help of meteorological station in the area of botanical garden, SUA in Nitra. The mean monthly air temperature and average rainfall for the year 2016 were evaluated by the climate normal 1961 – 1990.

In the experiment we investigated the effect of foliar nutrition with Tecnokel Amino Zn on selected quantitative and qualitative parameters in the following variants:

1^st variant (C) – (control) without applying of Tecnokel Amino Zn.

For both variants, based on the agrochemical analysis of the soil and the recommended normatives for the cultivation of sweet corn, we applied nitrogen one week before sowing in the form of nitrogen fertilizer LAD (27% N) (60% of the recommended normatives for corn) at a dose of 72 kg.ha^-1. When plants were 50 cm tall, we applied 40% of recommended LAD normative (27% N) in dose 48 kg.ha^-1.

Sowing the seeds was into pre-prepared soil on April 26, 2016. Before sowing, we made soil air spacing and removed the weeds. The seeds were sown in space 0.8 m between rows and 0.3 m within rows. During the vegetation. the supplementary irrigation was applied, as well as loosening and weeding of the crop. As corn tended to expel side shoots, we removed them on 8 June.

In the growth phase of 6 – 8 true leaves, (06.06.2017) we applied foliar fertilizer Tecnokel Amino Zn, which plays a key role as a building material and a regulating factor of wide range of enzymes and positively influences the transport of substances in the plant. The dosage of application was 30 mL.10L^-1 of water applied to the Tecnokel Amino Zn variant. The second application of Tecnokel Amino Zn with dosage 30 mL.10L^-1 of water was carried out on 21^st July after flowering.

Harvesting of sweet maize ears was carried out gradually according to the maturation of individual varieties, in the period from 26t^h July to 1^st August in the milky matured grains stage. Within each variety we evaluated 15 plants from the control and 15 from Tecnokel Amino Zn variant.

In the labs of the Department of Vegetables production at SUA we evaluated the following parameters: weight of one corn cob, length of corn cob, the number of grains per row and the number of rows per cob. Based on the average weight of maize cobs and cultivation spacing, the total yield was calculated.

Qualitative characteristics were estimated in the laboratory of Department of Vegetable Production, SUA, in Nitra. For laboratory analysis were used only fresh corn ears in phase of milk grains within of all observed varieties. Weight of one sample – 20g. Both control as well as the Tecnokel Amino Zn variant were observed. Fresh fruit analysis took a place directly after each harvest. Total carotenoids were estimated by spectrophotometric measurement of substances absorbance in petroleum ether extract on spectrophotometer PHARO 100 at 450 nm wavelengths according to Hegedüsová et al. (2015). The determination of total sugars according to Somogyi (1952) was carried out at the Department of Agrochemistry and Plant Nutrition.

The analysis of variance (ANOVA), the multifactor analysis of variance and the multiple Range test were done using the Statgraphic Centurion XVII (StatPoint Inc. USA).

The content of total carotenoids in selected varieties of sweet corn grains without foliar application of Zn ranged from 0.75 to 1.35 mg.100g^-1 of fresh matter. In the Tecnokel Amino Zn variant, the values ranged from 0.65 to 1.83 mg.100g^-1. The highest content of total carotenoids was recorded in the variety Escalante 1.83 mg.100g^-1 for observed variant. The positive influence of Zn on the content of total carotenoids was observed in varieties Rising Sun, Astronaut, ZHY 1312 OR, Escalate and ZHY 0874 OV (Figure 1). In different experiment Howe and Tanumihardjo (2013) reported higher carotenoid content in four varieties of sweet corn ranged from 0.99 to 3.53 mg.100g^-1.Based on statistical evaluation of our data obtained by the multifactor analysis of variance, we can state that the variant hadn´t significant influence on the total carotenoids content in fresh corn grains (Figure 4). Effect of the variety on the total carotenoid content wasn´t statistically significant.

Based on the results, we can conclude that all evaluated varieties of sweet corn belong to the Sh-2 group with a storage period of 4 – 7 days. The total sugar content ranged from 3.85% to 8.60% what is comparable with results of Zaniewicz-Bajkowska et al. (2010). They observed the total sugars content in sweet corn in range from 5.61% to 9.02%. In our experiment, the lowest content was recorded for variety ZHY 1312 OR 3.85%. Overture variety obtained highest value of 8.60% (Figure 2). By foliar application of Tecnokel amino Zn at a dose of 30 mL.10L^-1 of water, we found that the ingested preparation had no statistically significant effect the increase of total sugars in corn grains (Figure 5). Based on statistical analysis, we can conclude that the genotype has a significant effect on the total sugars in the grains at the stage of milk maturity.

Haytova (2013) in her review referred that additional foliar application during the growth and development of crops can improve their nutrient balance, which may lead to an increase in yield and quality of crops. Harvesting of maize in our experiment proceeded gradually according to maturation of individual varieties. The average calculated yield achieved in individual varieties and variants is compared in (Figure 3).

During the evaluation of total corn cob yield, we found that within the control variant, total yield ranged from 8.97 t.ha^-1 in SF 681 variety to 12.52 t.ha^-1 in Escalate variety. However, the highest hectare yield was 13.14 t.ha^-1 for the Overture variety without the application of the foliar fertilizer. Similar result was observed also by Rosa (2015), where the average marketable ears yield was 13.0 t.ha^-1. The lowest yield per hectare in our experiment reached the SF 681 variety with 8.97 t.ha^-1. However, the greatest difference between crops was recorded for the ZHY 1312 variety in favour of the Tecnokel Amino Zn variant 24.01% (Figure 3). Similar results stated also Fahrurrozi et al. (2016). In their study additional foliar fertilization of sweet corn did not significantly influenced growth and yield. Szczepaniak et al. (2018) event stated that zinc (Zn) fertilizers applied to maize simultaneously with amino acids (AA) at early stages of its growth may decrease the yield variability due to correcting its nutritional status during the ‘critical window’ but simultaneously confirm the benefits in order to ameliorate the influence of abiotic stress. However, this combination has positive effect on lettuce plants (Ghasemi et al., 2013). Grzebisz et al. (2008) wrote that according to other authors maize plants responded to zinc fertilizer and yielded 10 – 20% more. It supported by positive result of (Tariq et al., 2014; Liu et al., 2016; Ruffo et al., 2016, Shabaz et al., 2015). However, our result may be influenced by an inappropriate proportion of the nutrients applied. Shabaz et al. (2015) concluded that this significant enhance of corn yield is because trace elements had a synergic affiliation with other units. Wang et al. (2017) and Iqbal et al. (2016) also state that Zn combined with K or N can slightly or significantly increased grain yield. The influence of Zn uptake and its effect on corn yield depends on Zn supply in soil (Eteng et al., 2014), what should caused our results. All these results are in consonance with da Silva et al. (2017) exhibited increase in corn yield by 0.342 t.ha^-1 with 83.7% probability of positive response after foliar application of amino acid bio stimulant. Popko et al. (2018) confirmed these results. Amino acids bio stimulants increased wheat grain yield and agronomic productivity.

Foliar supply of Zn in the form of complexed with amino acids resulted in a significant increase of total yield and quality also for other species, for example pistachio nuts (Najizadeh and Khoshgoftarmanesh, 2018) or soybean (Teixeira et al., 2018). Using the statistical analysis of variance, statistically significant differences in total yield were not proven between the evaluated varieties or variants.

The weight of the corn cobs is one of the most important features for growers when choosing the right variety of sweet corn. During evaluating the weight of the cobs, we found that the highest average weight reached the variety Overture 315.5 g. The lowest average weight was recorded for variety ZHY 0874 OV 218.3 g (Table 5). In the Tecnokel Amino Zn variant, we noted an increase in the weight of the maize-ears for 3 genotypes: Astronaut (by 18.87%), ZHY 0874 OV (by 18.96%) and ZHY 1314 OR where foliar fertilization involved to the highest ears weight grain by 23.92% with average value of 259.7 g. By statistical analysis, we found a statistically demonstrable effect of the variety (genotype) on the weight of the maize ears. We also found that foliar application of Tecnokel Amino Zn fertilizer did not have a statistically significant effect overall, but significantly influenced some individual varieties (Table 5).

Barátová (2012) in her work reported results from the evaluation of 8 different varieties of sweet corn. Their ear length ranged from 18 cm to 21 cm. The average length of the strains in our experiment was quite similar and ranged from 19.3 cm to 25 cm. Highest value was caused by extremely long genotype Escalante, which reached average length of corn cobs 25 cm for control and 24 cm for Tecnokel amino Zn variant (Table 6). Due to the foliar application of fertilizer, we observed a slight increase in length for five varieties: Rising sun F1 3.13%, Astronaut 0.51%, ZHY 0874 OV 1.51%, SF 681 1.50%, Overture 1.82%. Statistical evaluation of results showed a statistically significant influence of the variety on ears length (Table 6), but the application of foliar fertilizer Tecnokel Amino Zn did not have a statistically significant effect on the length of corn cobs. It was similar in study Tadros et al. (2019) where foliar application of amino acid bio stimulant on sweet corn did not show significant effect on sweet corn ears.

Strube D&S GmbH gives the following characteristics for cultured genotypes: Rising sun F1 – 14, Astronaut – 20, ZHY 1312 OR – 20, Escalate – 18, ZHY 0874 OV – 18, SF 681 – 20, Overture – 20. For sugar corn, the number of rows in the ear should be even. In our experiment we recorded average number of rows in the interval between 16 – 21 rows. The highest average value in the number of rows in width 21, was recorded in the Overture variety. By applying zinc to this variety, we have not seen any greater increase in the number of rows. The smallest average values were recorded for the variety Rising sun F1 with 16 rows, but this is more than what the seller report. Also, for variety Overture was measured 8.62% fall in number of rows compared to variant with foliar fertilizer (Table 7). Average values obtained from our tested maize ears were comparable with Barátová (2012). She referred that the average number of rows in ranged with the width of 16 – 18. After statistical analysis of the variance, we found a statistically significant effect of the variety on the number of rows in the ear, but at the same time the effect of the foliar fertilizer Tecnokel Amino Zn was not significant (Table 7).

Number of grains in one row ranged between 34 – 49. The highest average values obtained genotype Escalate with yield 49 grains. The ZHY 1312 OR variety showed the lowest number of grains in row with 34 grains, but for this variety can be declared greatest increase over control variant with 10.81%. In addition to this variety, the number of grains increased in two more cases: ZHY 0874 OV and Astronaut (Table 8). Similar result referred Mosavifeyzabad et al., (2013). They confirmed positive effect of Zn fertilizer on number of corn grains in one row. However, based on statistical analysis of the variance, variety has a significant influence and increase in the number of grains in a row within the variant Tecnokel Amino Zn was not statistically confirmed (Table 8).