Potassium fertilization of rainfed olive orchards

Experiments under both greenhouse and field conditions were performed to study the influence of the type of salt applied (KCl or K2SO4) and to compare the effectiveness of their method of application (soil versus foliar) on leaf K concentration and yield in olive trees established under rainfed conditions. In the experiment performed in the greenhouse, mist-rooted 3-month-old ‘Picual’ olive plants growing in 2-l pots containing perlite were irrigated with a complete nutrient solution containing either 0.05 or 2.5 mM KCl during 128 days after transplanting (DAT). A group of plants received one K soil application at a dose equivalent to 1 kg of K per tree at 63 DAT. Another group received four foliar applications at 63, 78, 93 and 108 DAT with a K concentration of 10.5 g/l. The experiment under field conditions was developed with 80-year-old ‘Hojiblanca’ olive trees. Soil application was performed in March every year at a rate of 1 kg K/tree by injecting K fertilizer around the trees. Foliar sprays were carried out in April, March, June and July every year with the same K concentration used for the greenhouse experiment. The results showed that, under both field and greenhouse conditions, either KCl or K2SO4 increased K concentration in leaves. Also, both K salts had a positive effect in increasing K content in fruits under field conditions, although the intensity of the increase varied among years. Tree water stress and low K status seemed to influence K uptake. The method of K application, soil or foliar, did not affect the effectiveness of K fertilization.