INTERACTIVE EFFECTS OF SALINITY AND NITROGEN NUTRITION ON VEGETATIVE GROWTH OF APPLE-TREES

The interactive effects of N nutrition and salinity on the vegetative growth of 'Golden Delicious' apple trees on M26 and M9 were examined i n an outdoor pot experiment during 1989-1991. During the course of the experiment, the growth medium was salinized with 30 mM sodium salts; half of the number of trees was grown on the NaCl-medium, the other on the Na2SO4-medium. Three different nitrate levels were imposed (4, 8, and 12 mM). In spite of salinity, shoot and leaf growth was significa ntly increased by raising solution N concentrations from 4 to 8 mM, al though trunk growth was slightly reduced. The stimulation of growth by addition of N probably resulted from increasing uptake of NO3- and ot her essential ions and decreasing accumulation of salt ions. M26 seems to be more sensitive to salt stress when N was limiting than M9 and c onsequently responded more readily to the addition of N. NaCl-salinity seems to be more damaging to the trees than Na2SO4-salinity; possibly due to Cl-toxicity and Cl-induced NO3-deficiency.