Thomson navel orange (Citrus sinensis cv Thomson navel) belongs to the citrus family. Citrus fruits are grown commercially in more than 60 countries of the world in tropical and subtropical regions. Iran is also one of the areas prone to citrus cultivation (both in the north and in the south of the country) and has made great progress in the field of citrus cultivation and production.
Most of the novel oranges are seedless, short, relatively resistant to cold, and are productive all year round. Plant hormones are involved in the process of fruit shedding. Auxin is one of the important regulators of plant growth that is used in the management of shedding.
One of the ways to meet the nutritional needs of plants with mineral elements is foliar feeding. In this method, the elements required by the plant are provided to the plant quickly and with high efficiency. Reducing the use of chemical fertilizers and the resulting environmental consequences, such as groundwater pollution and soil structure destruction, is one of the characteristics of this fertilization method. Foliar spraying is considered as a supplement or alternative to the soil method.
Foliar spraying of nitrogen in spring is more effective than using it in the soil and increases the formation of seeds, fruit and yield of perennial fruit trees, including oranges of the Valencia variety.
The need for nitrogen reaches its maximum amount during the period of flowering and fruit formation, so the effect of nitrogen foliar application on plant nutrition is greater compared to adding it to the soil. In most cases, nutritional foliar spraying is done in spring and in some cases in summer. Several researches have shown that urea spraying can be a very efficient method to supply the nitrogen required by the plant at certain times and should be considered in nutritional management programs to store at least part of the nitrogen required by the tree. Foliar spraying of nitrogen in grapefruit increases the percentage Fruit formation, number of flowers, fruit weight and size.
Increasing the amount of nitrogen in flower buds increases the time of pollination, egg life, insemination and leaf area in grapefruit. As a result, the number of fruits is more and also bigger in terms of size, therefore, the yield of the plant increases.
In case of boron deficiency, the flowers fall due to impotence or even smaller fruits are produced. Boron causes the formation of pectin in the cell wall, cell division, synthesis of malic acid, transport of carbohydrates and enzymes.
Zinc is one of the most important and scarce food elements. After nitrogen, zinc deficiency is the most common nutritional abnormality in citrus fruits. Among the signs related to the lack of this element in plants, we can mention the shrinking of the terminal leaves, the falling of the leaves, and the decrease in the number and size of the fruits due to the lack of production of auxin hormone in the condition of zinc deficiency.
The results of this research on Thomson Nowel oranges have shown that the simultaneous use of urea with a concentration of 3 parts per thousand and boric acid with a concentration of 0.5 parts per thousand and at the rate of 69.83 kg per tree produces the highest yield and also the simultaneous use of urea with A concentration of 6 per thousand, boric acid with a concentration of 0.5 per thousand and zinc sulfate with a concentration of 3 per thousand with a yield of 68 kg per tree were also investigated. Also, the obtained results indicate that foliar spraying with nitrogen, boron and zinc nutrients has a positive effect in preventing the fall and increasing the formation of fruits in different phenological stages, especially the stage of final fruit formation, which increases the yield; As the percentage of fruit formation in trees increases, the yield also increases noticeably.
In a research, they investigated the effect of nitrogen, zinc, and boron fertilizer application on fruit formation and fruit yield of Samarkandi black grape variety. The results showed that the highest yield was obtained by foliar application of urea fertilizer, zinc sulfate and better quality boric acid with concentrations of 3, 4 and 1 g/liter. Also, foliar spraying of the combination of zinc sulfate with a concentration of 0.5% and urea with a concentration of 1% on orange trees of the Italian variety caused a 60% reduction in fruit fall compared to the control and as a result increased yield in these trees. The use of zinc sulfate as foliar spraying with concentrations of 2 and 3 per thousand has had a significant effect on increasing fruit yield compared to the control in Sangin oranges. The use of nutrients zinc and nitrogen has increased the number of fruits, increased yield and yield in tangerines of Tusrokh variety.
General conclusion
According to the results of this research, foliar application of nutrients nitrogen, boron and especially zinc with the effect of increasing the amount of auxin in the calyx region of the fruits reduces the fall and as a result increases the fruit formation in all three stages of early fruit formation, fruit formation after June fall, fruit formation final and as a result increased performance in Thomson Novel oranges. Foliar spraying of nutrients nitrogen, boron and zinc had a significant effect on the length and diameter of fruits.
Among the chemical fertilizers of Yadangar Structures Company (Cinco) that help the growth of citrus fruits, we can mention zinc sulfate and fructose (containing urea, boric acid, and zinc sulfate).
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