The Roles of Nitrogen, Phosphorus and Potassium on Olive Tree Productivity

The independent effects of irrigation solution N, P and K concentrations on flowering and fruit set in olive trees (Olea europaea L. 'Barnea') were studied over three successive seasons in a container experiment. Treatments included eight levels of N ranging from 5 to 202 mg/L, seven levels of P from 0.2 to 20 mg/L and seven levels of K from 10 to 208 mg/L. In spite of large variation in fruit load between the three seasons, the general trends were repeated annually. At low concentrations of each of the minerals, additions led to large increases in their contents in leaves and, as the concentrations became high, relative increases in leaf accumulation were reduced. Availability of both N and P was found to influence flowering intensity in the olive trees while K had only a minor affect. Fruit set was affected by both N and P but not K levels. Total fruit load of olives was a function of combined flowering and fruit set levels. Fruit load increased to a maximum as leaf N increased from 0.8% to approximately 1.7% and then decreased as leaf N further increased to 2.0%. Fruit set and thus the number of olives per tree increased appreciably as leaf P increased. The relative increases in fruit load tapered at the highest measured leaf P contents. Maximum fruit load was found corresponding to approximately 0.2% leaf P. Fruit load was not influenced by leaf K concentration. The findings indicate that N and P play fundamental roles in processes affecting olive-tree productivity.