The effect of fruit position in the canopy and potassium and calcium foliar ‎application on physico-chemical characteristics of ‘Thomson Navel’ sweet orange

In order to study effect of foliar application of calcium (Ca) and potassium (K) and fruit position in the canopy on physicochemical characteristics of ‘Thomson Navel’ orange trees (Citrus sinensis L. Osbeck, a two-year factorial experiment based on randomized complete blocks design carried out with two factors including the type of foliar spray in four levels (Ca(NO3)2, KNO3, Ca(NO3)2+KNO3, and Control) and fruit position in the tree canopy in two levels (inside or outside) with three replications. The results showed that peel thickness, citrus color index (CCI), and a ratio of total soluble solid to titratable acid (TSS/TA) were higher in the fruits harvested from the outer canopy compared to the canopy inside (P<0.05). Also, the results showed that the peel thickness of the fruit increased with foliar application and the highest increase was found in the foliar spray of K and K+Ca. With Ca foliar application (Ca and K+Ca), TSS and TA significantly decreased compared to the control and potassium foliar application alone, but the ratio between the two indices increased. The results showed that the effect of foliar application on total phenol and antioxidant capacity depends on the position of the fruit on the tree canopy. In conclusion, foliar application of K and Ca cause improve the fruit quality of the ‘Thomson Navel’ sweet orange. Besides, fruit at different canopy positions vary in their physicochemical characteristics and should be harvested separately to have uniform quality and get the maximum economic return.