Bahareh Rahmani - Department of Horticultural Science, Guilan University, Rasht, Iran
Mahmoud Ghasemnezhad - Department of Horticultural Science, Guilan University, Rasht, Iran
Reza Fotouhi Ghazvini - Department of Horticultural Science, Guilan University, Rasht, Iran
Akbar Forghani - Department of Soil Science, Guilan University, Rasht, Iran

Purpose: Boron deficiency can be a limiting factor for the flowering and fruit production of olive orchards. The appropriate time for foliar spray needs to be found in each environment. Research method: Effect of foliar spray (۳۵۰ mg L-۱ from boric acid) after fruit harvest (Stage ۱), during flower bud differentiation (Stage ۲), and the anthesis (Stage ۳) alone or in combination, on fruit set percentage, leaf and inflorescence boron, zinc, and iron concentration, soluble carbohydrates content in leaves of three commercial olive cultivars was investigated. Findings: Results showed, the maximum fruit set percentage, the highest leaf and inflorescence boron content, was found in the Koroneiki cultivar when boron sprayed two times at stages ۱+۳ and stages ۲+۳. The highest leaf and inflorescence zinc content was found when boron sprayed two times at stages ۲+۳ on the Koroneiki cultivar. The highest leaf and inflorescence iron content was found in Baladi and Mission cultivars, respectively, when sprayed at stage ۲ or two times at stages ۱+۳. Olive cultivar Baladi showed the highest leaf fructose, sucrose, and glucose content when boron sprayed at stage ۲ alone or three times at stages ۱+۲+۳. Research limitations: It can be useful to study different concentrations of foliar spray and other cultivars. Originality/Value: The response of different olive cultivars was not the same. It seems that boron spray at the appropriate time increased fruit set percentage, especially in Koroneiki. Therefore, more research is needed to find the best fertilization program in olive orchards of Golestan province.

foliar spray, Fertilization, Iron, Soluble carbohydrate, Zinc