Foliar Application of Potassium Nitrate and Silicate Can Improve the Fruit Quality of Pomegranate cv. ‘Malase Yazdi’

Pomegranate is an ancient fruit plant, that nowadays there is an increasing worldwide demand for this fruit owing to its superior pharmacological and therapeutic properties. Foliar nutrient applications could potentially be used in commercial pomegranate production, to improve fruit quality. Therefore, the current study was conducted to investigate the physicochemical properties of pomegranate fruits under foliar spraying of potassium nitrate and silicate.

The twenty years old uniform pomegranate trees cv. ‘Malase Yazdi’ that have grown on a commercial orchard in Ardakan, Iran were selected during the 2017–2018 growing seasons. Five levels of potassium spraying treatments were used. The foliar spray treatments included: 250 and 500 mg/l potassium nitrate; 250 and 500 mg/l potassium silicate and distilled water (control). The foliar spray was carried out two times. The first stage was after the conversion of most of the flowers to the fruit and when fruits reached about walnut size, from June to July, and the second stage of the foliar application was at the end of the fruit growth, in mid-September. At the time of the harvest, healthy fruits were taken from the middle of the crown of each tree in different directions, and qualitative and quantitative characteristics of the harvested fruits were analyzed. Physicochemical properties such as fruit and total aril weight, seed dry weight, peel fresh weight, fruit volume and juice, soluble solids concentration (SSC), maturity index, color, total phenol content, and vitamin C were investigated. 

Results showed that all of foliar treatments increased  fruit volume and weight, total aril weight, fruit juice, and color and decreased seed dry weight, compared to control treatment (without nutrient treatment). KNO3 (250 mg/l) increased SSC and maturity index and 500 mg/l KNO3 increased both valuable characteristics: total phenol and vitamin C content. Also potassium silicate improved vitamin C content compared to the control treatment.

The nitrogen in potassium nitrate increases the amount of the carbohydrate reserves that affects the fruit growth and development, thus reducing water stress and competition between fruits, which leads to the increased growth and development of fruits. The use of foliar application of potassium silicate has many advantages in enhancing the leaf area and improving the efficiency of photosynthesis and increasing the plant's ability to increase growth and yield and to increase strength, and reduce temperature stress. Therefore, according to these results, and due to the increasing global desire to use pomegranate fruit because of its high nutritional value, foliar application of potassium nitrate and silicate is recommended in pomegranate orchards.