Effects of Foliar Application of Calcium Chloride and Potassium Sulfate on Physical and Biochemical Properties of Jujube Fruit (Ziziphus jujuba Mill.)

Jujube (Ziziphus jujuba Mill.) as one of the invaluable medicinal plants, is widely used in the pharmaceutical industry due to its vitamins, mucilage, antioxidants, alkaloids and phenolic compounds. South Khorasan province is the most important area of jujube fruit production in Iran. Optimum supply of nutrients in fruit trees can increase fruit quality. Calcium is one of the most important elements that can affect quantity, quality, storability and marketability of many horticultural crops. Due to the relatively high amount of lime in the agricultural soils of South Khorasan province, the amount of calcium in these soils is almost high. However, due to low mobility of calcium from soil to plant, calcium deficiency is common in horticultural plants. Also, potassium is required for cellular osmotic and ionic balances, electrochemical processes, neutralization of organic acids, regulation of stomatal function, cell division, enzyme activation, protein synthesis, as well as the synthesis and translocation of sugars. Foliar spraying is an effective way to supply nutrients needed by plants, especially in calcareous soils with high pH. In this method, nutrients are directly available to different parts of the plant in a short period of time. Studies have shown that leaf feeding with calcium and potassium can be useful for increasing the qualitative characteristics of fruit in most products, especially in arid and semi-arid regions. Nevertheless, little information is available regarding the foliar application of this element on jujube plant. Hence, the current research was aimed to investigate the effects of foliar application of calcium chloride and potassium sulfate on physicochemical properties and quality of fresh jujube fruit.
 
In order to investigate the effect of foliar application of calcium chloride and potassium sulfate on the physical and biochemical properties of the fruit of the jujube plant, two separate factorial experiment was conducted in the form of a randomized complete block design in three replications in two areas of Siojan and Mazhan, Khosef city in 2022. Experimental treatments included calcium chloride (0, 0.5 and 1%) and potassium sulfate (0, 0.1 and 0.3%). Fresh fruit was harvested at a crisp mature (white-red) stage mid in August. Data were analysed using SAS software (ver. 9.4) and comparison of means was made with LSD test at 1 and 5% probability.
 
The results of analysis of variance showed that calcium chloride foliar application in Siojan garden had significant effect on the physical and biochemical characteristics of jujube fruit. So that the highest fresh weight (4.07 gr), dry weight (1.89 gr), length (29.11 mm), diameter (21.52 mm) and texture firmness (18.81 N/cm2) of fruit were obtained from the level of 0.5% calcium chloride. Also, the foliar spraying treatment with 0.5% calcium chloride had the highest amount of carotenoid and total phenol in the fruit. The highest amount of calcium and potassium in the fruit was obtained from the level of 1% calcium chloride. The effect of foliar application of calcium chloride on physical and biochemical properties of jujube fruit in Mazhan garden was significant. In Mazhan garden, the highest fresh weight (3.9 gr), dry weight (1.37 gr), length (28.41 mm), diameter (20.91 mm) and texture firmness (18.61 N/cm2) of fruit were obtained from foliar application of 0.5% calcium chloride. The highest amount of carotenoids (0.443 mg/100 g of fresh weight) and phenol (9.53 mg of gallic acid per 100 g of fresh weight) in Mazhan garden was obtained from the level of 0.5% calcium chloride. The content of calcium and potassium of jujube fruit in Mazhan region was maximized with the application of 1% calcium chloride. The results showed that the application of potassium sulfate in Siojan garden had an significant effect on the physical and biochemical characteristics of the fruit. The highest fresh weight (3.63 gr) and dry fruit weight (1.89 gr), length and diameter and texture firmness  of fruit was obtained from the level of 0.3% potassium sulfate. Also, the highest amount of biochemical indices of jujube fruit in Siojan garden was obtained from the level of 0.3% potassium sulfate. The interaction effect of foliar application of calcium chloride and potassium sulfate on fresh and dry fruit weight, fruit length and carotenoids of fruit in Siojan garden was significant. In Mazhan garden, the fresh and dry weight of fruit, amount of carotenoids and total phenol of fruit were affected by the interaction effect of experimental treatments, and the highest level of these characteristics was obtained from the level of 0.5% calcium chloride and 0.3% potassium sulfate.
 
The results of foliar spraying of calcium chloride and potassium sulfate in both studied orchards showed that these treatments, both solely and in combination, had a positive and significant effect on various characteristics of jujube fruit. So the highest physical and biochemical characteristics of the fruit were obtained from the simultaneous application of 0.5% calcium chloride and 0.3% potassium sulfate. Therefore, Based on the results of this research, foliar spraying 0.5% calcium chloride and 0.3% potassium sulfate can have an effective role in increasing the quantity and quality of jujube fruit.