The aim of this research was determine the Ca concentration in citrus fruit peel and different vegetative organs, trend of Ca changes in fruit peel during growth season and the role of its using in phonological key stages of Thomson navel orange in increasing relative yield and fruit quality. By sampling from internal and external part of tree canopy, leaves, shoots and roots, Ca concentration
... [Show full abstract] was determined also effect of Ca(NO3) foliar application after fruit set, before physiological drop and in the late of second phase of fruit growth was evaluated in RCBD with 4 treatments and 4 replications. Results showed that fruit diameter in internal of canopy was more than it in external of canopy but Ca concentration in fruit peel of internal of canopy (about 0.43%) was lower than it in external of canopy (about 0.52%). Also, trend of Ca concentration change in fruit peel of internal of canopy has more fluctuate during growth season. The highest yield, fruit diameter, fruit weight and Ca concentration in fruit peel was obtained from Ca spraying after fruit set and before fruit physiological drop. In spite of this results, the most suitable time to Ca spraying in citrus, is first stages of fruit growth. Therefore, CaNO3 spraying after fruit set and before summer physiological drop was recommended.