Effect of combined foliar application of calcium and potassium on the shelf life and quality of Thomson Navel orange

The shelf life of orange ‘Thomson Navel’ (Citrus sinensis var. Thomson Navel) is low. One of the important factors in maximum increase of fruit quality and its nutritional value is the presence of calcium and potassium in fruit tissue. Absorption of essential elements from the soil by the roots and their transfer to the aerial part of the plant, including entry into the fruit tissue are important challenges. Calcium deficiency in citrus fruits is possible due to reduced absorption from soils. The application of these elements in the form of foliar application solves this challenge. The aim of this study was to determine the appropriate frequency of combined treatment of calcium and potassium (one to four times), before and after harvest, on shelf life and fruit quality of Thomson Novell cultivar, including calcium, vitamin C and soluble solids (°Brix).

Treatments were without foliar application of calcium, once foliar application of calcium (in June), twice foliar application of calcium (in June and July), three times foliar application of calcium (in June, July and September), four times foliar application of calcium (in June, July, September and October), without foliar application of potassium, once foliar application of potassium (in June) and twice foliar application of potassium (in June and July), alone or in combination with a week distance and before harvesting fruits. After harvesting, all fruits were treated with 3 per 1000 calcium for 5 minutes as plunging. Fruits without foliar application of calcium and potassium were considered as controls. Calcium foliar application was performed at a constant rate of 3 per1000 and potassium foliar application at a rate of 2 per 1000. The last stage of treatment of fruits with calcium was done after harvest and by immersion in a solution of 3 per 1000. The experiment was conducted in a completely randomized block design with three replications in Kharik village of Sari city. The fruits were stored at the temperature of 5°C and 85% relative humidity for 3 months. Traits of length, diameter, skin diameter, weight, juice volume, decay, vitamin C, calcium, total solid soluble (TSS), titration acidity (TA) and acidity (pH) of fruits were measured after 3 months’ storage.

The results showed that the most vitamin C (97.69 mg/100 ml fruit juice), fruit weight (242.20 g) and fruit juice volume (115.70 ml) were obtained in fruits treated with twice foliar application of calcium (in June and July at a rate of 3 per1000) together with twice foliar application of potassium (in June and July at a rate of 2 per1000). The highest diameter (78.92 mm) and the lowest decomposition were obtained in fruits treated with twice calcium (June and July at a rate of 3 per1000) together with once potassium (June at a rate of 2 per1000). The highest amount of fruit calcium (165.30 g/kg DW) was calculated in the treatment of 3 times foliar application of calcium (in June, July and September at a rate of 3 per1000) together with once foliar application of potassium (in June at a rate of 2 per1000).

In general, based on the findings of this study, foliar application of Thomson Novell cultivar through twice calcium (in June and July, at a rate of 3 per 1000) and once with potassium (in June at a rate of 2 per1000) and twice with potassium (in June and July, at a rate of 2 per1000) before harvest along with plunging into 3 per 1000 of calcium after harvest (for all oranges) is suitable for maintaining the quantity and quality of fruits during storage and this treatment is recommended.