Foliar diagnosis as a guide to olive fertilization

Abstract

A long term experiment was established in olive orchards of Andalusia, southern Spain, to compare the fertilization practice based on foliar diagnosis versus the current fertilization practice in the area. Only nutrients whose concentration in leaves taken in July were below the critical levels were applied in the former treatment, whereas in the latter 500 kg/ha of a 15-15-15 complex fertilizer, and three foliar sprays of micronutrients and aminoacids were applied annually. Four olive orchards were selected. One orchard has a small effective depth (33 cm) limited by a petrocalcic horizon. The second has an effective soil depth of 60 cm, and is representative of broad level uplands on hard calcareous rocks. The third orchard has a deep soil (90 cm), typical of rolling areas with soft marls; and the fourth is a soil whose effective depth is also large (90 cm), representative of flat areas on soft clayey sediments, partially decalcified. One homogeneous zone of 2-ha was split into two plots within each orchard, and the treatments were randomly assigned to each plot. After five years, no significant differences were found in yield, fruit weight, oil content or vegetative growth, but polyphenols in the oil decreased in trees subjected to the traditional fertilization. Fertilization cost increased in more than 10 times in the traditional fertilization plots. Results indicate that the current fertilization practice apply more nutrients that needed for a good crop, negatively affect olive oil quality, and increase cost compared with foliar diagnosis.