The nitrate levels in function of the harvest times, and the sampling criterion of american type lettuce leaves were determined. The plants were harvested at UNIOESTE in Marechal Cândido Rondon, Paraná State, Brazil, at 0 o'clock, 6 a.m., 12 o'clock and 6 p.m. In sequence, the leaves were washed, discarding the central nervure, later they were separated according to mature leaves (external leaves), recently mature leaves (median leaves) and new leaves (internal leaves). The dry weight and the nitrate level were determined. Leaves harvested during the day presented lower values of nitrate levels in comparison to leaves harvested during the night. About the sampling criterion the nitrate levels were superior in new leaves, 999 mg of N-NO3-.kg-1 dry weight, while the mature leaves and the recently matured leaves accumulated 564 and 468 mg of N-NO3-.kg-1 dry weight, respectively.
Lactuca sativa L.; light intensity; leaf analysis; nutrition
