EFFECT OF LOWERING NUTRIENT SOLUTION CONCENTRATION AT NIGHT ON LEAF CALCIUM LEVELS AND THE INCIDENCE OF TIPBURN IN LETTUCE (VAR GLORIA)

Butterhead lettuce (var. Gloria) were grown in an evaporatively cooled glasshouse using the nutrient film technique (NFT). During the day all plants received a complete nutrient solution (EC 2 dS/m). Treatments were imposed at night and included: complete nutrient solution (control); tap water (EC 0.19 dS/m); and calcium nitrate solutions containing either 100 mg Ca/L (EC 0.80 dS/m), or 200 mg Ca/L (EC 1.45 dS/m). Tipburn occurred in the control and its incidence was reduced by the other treatments. This effect was associated with an increase in the concentration of calcium in new leaves, except in the water treatment. The night treatments did not affect the fresh weight of mature lettuce. Circulation of either water or calcium nitrate (100 mg Ca/L) at night may, therefore, be a commercially acceptable means of reducing tipburn losses in lettuce crops grown using hydroponics.