NUTRIENT REFERENCE LEVELS FOR FERTIGATION SCHEDULING IN OLIVE GROVES OF AN ARID REGION OF ARGENTINA (SAN JUAN)

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The diagnosis of tree nutritional status in fruit trees by leaf-nutrient analysis allows for fertilization scheduling by fertigation. In olive, a specific equilibrium in leaf nutrient concentration occurs that depends on the dominant edaphic and climatic conditions as well as the time of year. Therefore, the objective of this study was to determine leaf-nutrient reference values in olive in an arid region of central-western Argentina at two different times of the year. Leaf samples were taken during the winter rest period (July) and summer (January; a month after pit hardening) over three consecutive years in 100 commercial olive orchards from several cultivars in the Tulum Valley of San Juan, Argentina. These periods have been proposed previously in other regions. Leaf nutrient contents were analyzed and the obtained values were compared with those reported elsewhere. Confidence intervals (95%) of nitrogen (N), phosphorus (P) and potassium (K) in the winter were 1.73-1.83, 0.14-0.16 and 0.92-0.98%; respectively, while summer values were 1.56-1.70% (N), 0.16-0.18% (P), and 1.14-1.26% (K). The N concentrations were somewhat lower than those reported for the mediterranean basin with P and K values in contrast being similar or greater. Values of the remaining nutrients (Ca, Mg, Mn, Na, Cu, Zn, B and Fe) were generally similar to those reported for the Mediterranean. However, boron levels were somewhat high in the winter (25.38 ppm), and magnesium (0.13%) and manganese (33.04 ppm) were low in the summer. Given that the winter period showed narrower confidence intervals than the summer period for N, P, and K, winter sampling could be considered for annual fertilizer scheduling in intensive olive orchards in arid central-western Argentina. However, sampling during the early summer period may provide critical information just prior to oil accumulation.