Relationship between climatic indicators and some physiological stages of navel orange trees in West Delta, Egypt

Field investigations, were performed during two successive growing seasons 2014 and 2015 to assess the suitability of a region for growing navel orange, also to estimate the length of various phenological stages and to predict suitable time for maturity of navel orange by using heat units requirement for this cultivar. The chosen Washington navel orange trees (Citrus sinensis L.) Osbek, budded on sour orange rootstock were ten-year-old, spaced at 5 × 5 meters and grown in clay soil, under flooding irrigation system in a private orchard located at Kafr El-Sheikh Governorate, Egypt. The results showed that each phonological stage (root activation, spring flush, flowering and color break) as well as the actual starting dates for each phase recorded more heat units in the second season than the first season, subsequently, the starting dates of each phase was earlier in the second season than first season except in case of color break. With respect to correlation between fibrous root growth and the temperature during both studied seasons, it is obvious that there was strong correlation between either number or weight of roots and soil temperature in both studied seasons. Regarding yield and fruit quality attribute, it is apparent that yield and fruit quality attribute were affected by the changes in the climatic conditions for each season.