Potassium utilization efficiency of three olive cultivars grown in a hydroponic system

- Significantly greater KUE values were found in the T3 and T4 treatments.
- 'Koroneiki' was the most K-efficient cultivar in the T3 and T4 treatments.
- K concentration affected the plant growth of 'Kalamon' and 'Arbequina'.
- Greater stomata opening were recorded in the highest (T4) treatment.
- The photosynthetic rate of 'Koroneiki' was not higher in the T4 treatment.

A hydroponic experiment was carried out in an experimental greenhouse in order to investigate if K level in nutrient solution affected the efficient use of K (KUE) of three olive cultivars, as well as if genotypic differences concerning KUE among them for the same K level existed. For that purpose, the effect of K concentration on growth, nutrient uptake and utilization efficiency, as well as on physiological functions (stomatal conductance, photosynthetic rate, transpiration and water use efficiency) of the olive cultivars 'Koroneiki', 'Kalamon' and 'Arbequina' was studied. Rooted leafy cuttings of these olive cultivars were grown for 55 days in 1:1 sand:perlite mixture and were irrigated with 50% modified Hoagland nutrient solutions, differing between them only in K concentration (0.50, 1, 5 and 20 mM KCl). Potassium concentration in nutrient solution influenced the growth of the cultivars 'Kalamon' and 'Arbequina', but not that of 'Koroneiki'. The influence of K concentration on macro and micronutrient uptake was in most cases non significant. Stomatal conductance was greater in the T4 treatment (at 35, 45 or 55 DAIT), compared to T1, T2 and T3, for all genotypes. However, only the photosynthetic rates of 'Kalamon' and 'Arbequina' (and not that of 'Koroneiki') were found to follow the tendency of greater stomata opening (at 35, 45 or 55 DAIT). The highest rate was observed in the treatment of 20 mM KCl in 'Kalamon', while the lowest one was found in the treatment of 1 mM KCl in 'Arbequina'; therefore, the reaction of photosynthetic operation of olive plants to K mineral nutrition was strongly K, as well as genotype dependent. Transpiration rates on the 35th and on the 45th day of the experiment were significantly affected by K mineral nutrition, in all olive cultivars. Regarding water use efficiency (WUE), the K treatment effect was significant only in 'Koroneiki' on the 35th day and in 'Kalamon' on the 45th day. No difference between treatments was recorded in all cultivars concerning WUE on the 55th day, though genotypic differences were significant ('Kalamon' was less water use efficient, compared to the other genotypes). Finally, 'Koroneiki' was more K-efficient than 'Arbequina' and 'Kalamon', especially in high K concentrations (5 and 20 mM KCl), so it should be preferred for cultivation in groves receiving rich K fertilizations.