The youngest fully expanded mature leaf of each plant was sampled from a factorial N and K fertilization field trial on July 4, August 22, October 27 and December 4. Nutrient uptake was not very active during the late autumn and winter. On the first sampling date no differences in leaf N content were observed among the different fertilization treatments, probably because of a dilution effect. During the remainder of the growing season, N fertilization generally affected leaf nutrient values. The levels of all the nutrients tested decreased during the harvesting period, but, with the exception of N, remained within the Californian standards. Nitrogen content decreased during the harvesting season to levels of about 1 %, for both fertilized plants and unfertilized controls, indicating that either no uptake was taking place during the late harvesting period, or that all N was being transported to fruit. Leaf K levels should not be higher than about 1.65% at the beginning of the harvesting season, as leaf levels of 1.80% were associated with soil K levels of 80 ppm, which resulted in decreased yield and fruit size. There is no single time at which leaves should be sampled for diagnostic purposes, and different standards for leave analyses should be developed for different periods during the growing season.