Response of mature 'Manzanilla' olive trees to different doses of N-P-K fertilizer applied by fertigation

Fertigation is widely used in the new intensive olive orchards, although there is not enough information for a rational management of this practice. Preliminary results of a fertigation experiment initiated in 1999 in a mature olive orchard of the cultivar 'Manzanilla de Sevilla' are presented. Four treatments were established: T1 (no fertilizer) and T2, T3 and T4, in which the trees received 200, 400 and 600 g N per tree and irrigation season (May to October), respectively, of a dose of a complex 4:1:3 N-P-K fertilizer applied by fertigation. The water used for irrigating the orchard had a nitrate content equivalent to 60 g N per tree, approximately. Vegetative growth, yield and some variables related to fruit and oil quality were measured in all the treatments. No significant differences between treatments were found on shoot length and yield. Some physical properties, such as mean fruit weight, flesh/stone ratio and volume, increased with the amount of fertilizer applied, while texture and reducing sugars decreased, affecting table olive quality. Oil quality was affected negatively by fertigation since polyphenol content, bitterness, stability and monounsaturated fatty acids decreased when the amount of fertilizer increased. The polyunsaturated fatty acids, however, increased when increasing the fertilizer amount.