1. Introduction
Meeting the population’s demand for food products and ensuring food security are among the most pressing issues today. For this, it is advisable to create scientifically based innovative technologies for the cultivation, storage, and processing of various food products throughout the year. Currently, the demand for melon products is increasing day by day. After all, melon, which is a product of melon crops, has several beneficial properties for human health. Uzbek melons are famous all over the world for their sweetness, unique taste, aroma, and long-term storage [1]. Melon fruits contain a large amount of potassium, calcium, magnesium, iron, sulfur, and some vitamins. The energy value of their fruits is on average 34 kcal, most of which consists of water. The main part of the fruit consists of carbohydrates, the rest of the protein, fat, ash, pectin, and organic acids [2] [3]. The seeds are also rich in biologically active substances (more than 25% fat, sugars, protein, and other compounds).
Currently, more than 160 varieties of melon are distributed in Uzbekistan, which differ from each other in terms of early ripening, yield, resistance to diseases and other adverse conditions, taste, storage, transportability, suitability for processing and drying, etc. The sugar content of melon varieties ranges from 10.4 - 14.9% [4] [5].
Many researchers claim that pre-sowing seed treatment with various methods ensures high yields. In studying the effect of pre-sowing seed treatment on improving melon yield, seed quality is improved by applying additional micronutrients to the soil before planting. Microelements are involved in many physiological and biochemical processes in the body from intracellular anabolism and catabolism to the reproduction of the organism [6].
Experiments have shown that by ensuring the need of plants for mineral elements, their drought resistance increases sharply. The effectiveness of fertilizers directly depends on the moisture supply of the plant. Therefore, in plants with sufficient water supply, their efficiency increases, as a rule, by 2 - 4 times. The proper functioning of each living cell depends solely on the presence of essential macro- and microelements [7] [8]. Furthermore, the accumulation of dry mass in plants was found to be influenced by alterations in the size of the feeding area and the conditions for providing nutrients [9].
2. Materials and Methods
The experiments were conducted in the conditions of the Samarkand region in 2023-2024. During the research, seeds of the Amiri and Kizil Gulobi melon varieties were used. Before sowing, the field was irrigated, and as the soil matured, pre-sowing tillage was carried out, and seeds of each variety were sown in 4 replicates (field surface (2.5 m × 80 m) 200 m2). The field was irrigated 3 times (650 - 700 m3/ha) during the growing season.
In field experiments (5 variants), the following micronutrients were applied to the soil against the background of macro fertilizers (N220P110K70 background): copper—10 kg/ha, zinc—20 kg/ha, manganese—15 kg/ha, and cobalt—5 kg/ha. Also, for foliar feeding, solutions of 0.05% copper (CuSO4 * 5H2O), 0.01% manganese (MnSO4 * 5H2O), 0.05% zinc (ZnSO4 * 8H2O), and 0.01% cobalt (CoSO4 * 7H2O) were sprayed onto the leaves once during the leaf budding period of the plant. Ammonium nitrate, PS-agro, and potassium chloride were used as mineral fertilizers.
Samarkand region is characterized by very diverse natural and geographical conditions. Various soil types are distributed in the natural and geographical conditions of the region [10]. Typical gray soils with medium and light loamy loams, mainly located in deep layers of groundwater, are widespread in the Samarkand region, and these soils account for 38% of the total area of the region. The rest are almost light gray soils, found in the western and southwestern parts of the region. In addition, meadow, meadow-gray, and gray-meadow soils are also widespread [11].
Before sowing in sand, seeds were soaked in 0.1; 0.05 and 0.005% solutions of various microfertilizers for 12 hours, in which the seeds and solution were taken in a 2:1 ratio. At the same time, the option was used as a control that was soaked in distilled water and sown in soil. In laboratory experiments, each variant was planted in 8 replicates, a total of 100 seeds were sown in sand with a humidity of 70%, and germination energy and germination indices were recorded in a thermostat at 20˚C. Through these laboratory studies, the most favorable concentrations were determined, and field experiments were conducted on this basis.
All observations, analyses, and measurements were carried out based on the “Methodology of State Variety Testing of Agricultural Crops [12]”, and field experiments were conducted using generally accepted methods (Methods of Conducting Field Experiments, 2007 [13]; Methodology of Field and Vegetation Experiments with a Cultivator under Irrigation Conditions [14]. In the experiment, the following methodological manuals were used to perform agrochemical and agrophysical analyses: “Methods of agrochemical, agrophysical and microbiological studies in cotton irrigated areas [15]”, “Agrochemical methods of soil research [16]. Statistical analysis of the experimental results was carried out according to B.A. Dospechov [17]. In the experiments, the total nitrogen content in the leaves of melon varieties at different developmental phases was taken into account. The total nitrogen content in the plant was determined according to Ermakov [18], Kruglova [19], and Taraz [20].
3. Results and Discussion
Nitrogen (N) is one of the most important mineral nutrients for plant growth and biomass formation and is involved in the synthesis of amino acids, proteins, nucleic acids, lipids, chlorophyll, and various metabolites containing the nitrogen element. Since plants require nitrogen in the largest amount of any mineral element, nitrogen deficiency is a limiting element for plant growth and development [21]. Plant growth and development processes, including root development, leaf development, seed dormancy, and flowering, can be significantly affected by the amount and source of nitrogen supplied to plants. It has also been found that different nitrogen sources available in the rhizosphere significantly affect the amount of macro and micronutrients in leaves, and as a result, affect nitrogen metabolism, photosynthesis, plant growth, and yield in Citrus sinensis [22], cucumber [23], and watermelon [24].
Researchers have paid great attention to studying the effect of micronutrients on total nitrogen accumulation in plants. It has been found that manganese, boron, molybdenum, and cobalt increase total nitrogen in most crops. In our experiments, the effect of micronutrients on plant nitrogen content was also studied. As shown in Figure 1 and Figure 2, the total nitrogen content in leaves increased at different stages of plant development under the influence of micronutrients. We also observed a decrease in the total nitrogen content of melon varieties by phase, that is, from the 7-leaf stage to the fruit formation phase. We can say that the reason is the transport of nutrients, including microelements, from vegetative organs to generative organs during the fruit formation period.
According to the data obtained in the experiment, microelements had a significant effect on the total nitrogen content of leaves in different phases of development and on the number of male and female flowers in the plant. It was found that the total nitrogen content in both varieties increased from the 7-leaf stage of the plant to the flowering phase and decreased by the fruit formation period. In particular, the nitrogen content in the Amiri variety in the N220P110K70 background variant was 2.48 mg/kg at the 7-leaf stage, 2.73 mg/kg at the flowering phase, and 2.18 mg/kg at the fruit formation period, respectively (Figure 1).
Figure 1. Nitrogen content in leaves of Amiri (mg/kg).
Under the influence of microelements, the nitrogen content in the leaves of the Amiri variety increased compared to the N220P110K70 background variant, and the highest nitrogen content was observed in the variant with cobalt application. In particular, the nitrogen content in the 7-leaf stage of the Amiri variety was 2.48 mg/kg in the N220P110K70 background, while the highest was 3.16 mg/kg when cobalt was applied and as a result, cobalt increased nitrogen content by 27% in Amiri leaves during that stage of the vegetation period. The same result was observed in the flowering phase of the plant. The positive effect of cobalt on the plant is known from the scientific literature, as it was found that additional treatment with cobalt in cobalt-deficient soils had a positive effect on the total nitrogen content in some crops [25]. According to the research of A. L. Sanakulov, when cotton grown in cobalt-deficient conditions was additionally treated with cobalt, the energy efficiency coefficient increased [26] and this microelement had a positive effect on nitrogen metabolism in the plant [27]. On the contrary, in the 7-leaf stage of the Kizil Gulabi variety, the highest nitrogen content was observed when manganese was applied and was 2.95 mg/kg, respectively. In the flowering phase, the highest nitrogen content was observed when copper was applied, at 3.37 mg/kg and was accounted for 68,5 % increase (Figure 2).
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Figure 2. Nitrogen content in leaves of Kizil Gulabi (mg/kg).
In the Amiri variety, the highest nitrogen content during fruit formation was determined in the variant where the zinc microelement was applied—2.90 mg/kg which was made up 33 percentage of growth in nitrogen content. In the Kizil gulabi variety, the highest nitrogen content in the leaves was observed in the variant where cobalt was applied and was 3.12 mg/kg that resulted for 11,82 % rising in nitrogen content during fruit formation. In general, according to the experimental results, we can see that the zinc microelement had a positive effect on the nitrogen content in the leaves. The scientific literature also highlights the existence of a mutual relationship between zinc and nitrogen in the development of crops. According to the experiments of Meng Li et al., zinc application helps in the accumulation and assimilation of nitrogen. It was found that zinc application increased the activity of nitrate reductase and glutamine synthetase in wheat, millet, and rice and enhanced the assimilation of NH4+, and as a result, the concentration of amino acids and proteins increased [28]. On the contrary, zinc deficiency has been reported to cause disturbances in nitrogen metabolism, including decreased protein and free amino acid production and accumulation of amides in rice meristem tissues [29].
The number of flowers, including female flowers, formed in the melon plant is noteworthy. The results show that the Amiri variety formed the most male flowers under the influence of the cobalt microelement, 302.4 pieces, while the female flowers formed the most when manganese was applied and amounted to 18.2 pieces (Figure 3). The Kizil gulabi variety formed the most male flowers when zinc and manganese were applied, and amounted to 309.7 and 309.2 pieces, respectively. Similarly, the zinc and cobalt microelements affected the formation of the most female flowers, and 21.0 and 21.2 pieces of female flowers were formed, respectively (Figure 4). In the variants where manganese and zinc were applied, flowers, including female flowers, were formed in large numbers. Based on the result of the research, yield depends on the number of female flowers produced by the plant. For that reason, increasing the number of female flowers is vital to acquire the yield [30].
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Figure 3. Number of flowers in Amiri.
Figure 4. Number of flowers in Kizil Gulabi.
Manganese is an important component of the catalytic center that carries out the oxidation of water in photosystem II (PS II) and is necessary for the formation of energy and ATP required for CO2 assimilation. In addition, manganese is necessary for the activation of phosphoenolpyruvate carboxykinase [31] and lipid metabolism. It was found in experiments that when maize seedlings were treated with manganese, the net mass of one plant increased by 27.49%, while in conditions of manganese deficiency, the net mass of the plant decreased by 45.62% compared to the control [32]. It can also be seen that the effect of the trace element zinc on the plant was also significant during the experiment. Zinc is an essential trace element and plays an important role as a cofactor in many enzymatic reactions involved in protein synthesis, carbohydrate, nucleic acid, and lipid metabolism [33]. This indicates that adequate levels of zinc are crucial for maintaining optimal growth and development in plants. Further research is needed to explore the mechanisms through which zinc influences these metabolic processes and to determine the optimal concentrations required for different plant species.
4. Conclusion
Thus, in the conditions of the Samarkand region, the application of microelements to the soil and foliar feeding in the cultivation of melon varieties has a positive effect on the accumulation of nitrogen in the leaves of the plant, as well as on the formation of flowers (male and female) in the plant. For instance, by copper treatment, a 68,5 % increase was observed in nitrogen content in Amiri leaves during the flowering period. In the copper-applied option, 11,8% growth was indicated in the nitrogen content of Kizil gulabi leaves in fruit formation while there was a 33 % rise in nitrogen content of Amiri leaves during fruit formation when zinc was applied. As a result, a favorable nutritional regime is created for the plant, the yield increases and its quality improves. In general, according to the experimental results, we can see that the zinc, copper and manganese had a positive effect on the nitrogen content in the leaves.