Flowering and fruit set of olive trees in response to nitrogen, phosphorus, and potassium

The independent effects of nitrogen, phosphorus, and potassium concentrations in the irrigation solution on flowering and fruit set in olive trees (Olea europaea L. cv. Barnea) were studied in a container experiment. Treatments included eight levels of N ranging from 0.4 to 14.1 mM, seven levels of P ranging from 0.01 to 0.62 mM, and seven levels of K ranging from 0.25 to 5.33 nM. At low environmental concentrations of each of the minerals, additions led to large increases in their concentrations in leaves, and as the environmental concentrations became high, relative increases in leaf accumulation were reduced. Availability of N, P, and K was found to influence flowering intensity in the olive trees. Fruit set was affected by N and P, but not K levels. Total fruit load of olives was shown to be a function of flowering level multiplied by fruit set. The final number of olives per tree increased appreciably as leaf P and K increased from minimum levels, and relative increases in fruit load tapered at the highest measured leaf concentrations of the minerals. Maximum fruit load was found corresponding to ≈0.06 mol·kg^-1 P and close to 0.35 mol·kg^-1 K in leaves. Fruit load increased to a maximum as leaf N increased from 0.7 to 1.3 mol·kg^-1 and then decreased as leaf N increased to 1.5 mol·kg^-1. The findings indicate that each of the macronutrients plays a fundamental role in processes affecting olive tree productivity.