Abstract
The correct management (dose, time of distribution) of N fertilization in olive growing is still not completely clarified but is nowadays essential in order to guarantee sustainable production. In this regard, in central Italy over a 4-year-period a study was carried out to investigate the effect of high nitrogen availability during oil accumulation in the fruit (second phase of fruit growth) on vegetative and productive activities of olive trees and oil quality. In May of each year, secondary branches were selected and girdled in their proximal part. Afterwards, half of the girdled branches were sprayed three times with a solution containing urea (2% w/w), whereas the other half was sprayed only with water. The nitrogen treatments did not cause any damage to the foliage and fruits nor did it cause appreciable changes in leaf photosynthesis and specific weight, fruit-drop, ripening pattern and weight, water and oil contents, pulp/pit ratio of the fruits, fatty acid composition, polyphenols content, and sensorial characteristics of the oil. The N provided via foliar fertilization during the oil accumulation phase in trees in conditions of good supply of N does not induce significant effects on the vegetative-productive activity of the tree.
Highlights
Nitrogen is the mineral nutrient most commonly applied in olive (Olea europaea L.) orchards since it is a major nutritional factor affecting plant growth [1,2,3]
N shortage results in a marked decrease in plant photosynthesis since a great part of the total leaf N is allocated to the photosynthetic apparatus [4]
As a matter of fact, the response of leaf photosynthesis to N fertilization is largely dependent on the leaf N content [4]
Summary
Nitrogen is the mineral nutrient most commonly applied in olive (Olea europaea L.) orchards since it is a major nutritional factor affecting plant growth [1,2,3]. N, reduced number of flowers per inflorescence, low fruit set and yield [8,9,10,11]. N fertilization was reported to increase fruit set in olive [8]. Combining soil and foliar urea application was seen to be more effective in increasing leaf N than only soil application [12]. Multiple application of urea (2%) via foliar spray to olive trees with inadequate nitrogen status increased leaf N significantly but did not affect the percentage of flowering nodes or flower size at anthesis in May [13]
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