Abstract
Two experiments were carried out in olive orchards in the center of Spain over a three-year period. In this cold and dry area, growers traditionally apply large amounts of N with no experimental knowledge. An ‘Arbequina’ hedgerow and ‘Picual’ vase orchards were fertilized with two N-doses applied to the soil in spring with or without the nitrification inhibitor (DMPP). Vegetative growth, fruit and oil characteristics were evaluated. These variables were affected by the N-treatment during the 3rd year. The lowest N-application increased vegetative growth, while when N-leaf composition was higher than 2%, fruit dry weight, oil content and oil phenol content were reduced. ‘Picual’ did not respond to N-applications. The effect of DMPP on growth or production was not consistent and a lower phenolic content was obtained for ‘Arbequina’. Our results demonstrated that in this dry land, N-fertilization is not always necessary and oil quality can be negatively affected with high doses.
Highlights
The olive (Olea europaea L.) is one of the most important crops in the Mediterranean regions
Before the 1950s traditional olive orchards in Spain established at low plant densities (< 100 trees per ha) did not receive any fertilizer application
In Spain fertilization has been based on traditional management by applying the same fertilization program every year, without considering nutritional soil reserves or plant requirements (Fernández-Escobar, 2010)
Summary
The olive (Olea europaea L.) is one of the most important crops in the Mediterranean regions. The perception that annual applications of significant amounts of N-fertilizer represent cheap insurance against the economic risks associated with insufficient N availability is common among growers. This caused many olive orchards to be fertilized in excess, applying N annually at rates that range from 9 to 350 kg·ha−1 (Fernández-Escobar et al, 1994). An excess of N-fertilization could cause nitrate pollution and increase frost and disease sensibility It could negatively affect oil quality (Fernández-Escobar et al, 2006) because of a decrease in polyphenols, which are the main antioxidants (Erel et al.,2013)
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