INFLUENCE OF VAPOR-PRESSURE DEFICIT AND P HOTOPERIOD ON GROWTH, PRODUCTIVITY AND MINERAL-COMPOSITION ON GREENHOUSE TOMATO

The objective of this study was to determine the effect of four vapour pressure deficits (VPD) and three photoperiods on growth, yield and m ineral composition of tomato plants. A factorial experiment was conduc ted from 28 July 1993 to 30 May 1994 in a greenhouse at Laval Universi ty Envirotron in Quebec, Canada. Four day/night VPD treatments were co mpared: 1) 0,4/0,4 kPa, 2) 0,97/0,4 kPa, 3) VPD adjusted to a transpir ation rate of 800 mL d(-1) plant(-1) and 4) 0,97/0,97 kPa. For each VP D treatment, three photoperiods were used: 1) 12 h, 2) 14 h and 3) sea sonal progressive photoperiod of 12 to 16 h. The highest VPD significa ntly increased total and marketable yield, biomass and Ca, Mg, K, N an d P contents of the leaves. Results obtained with adjusting the VPD to transpiration needs showed no significant differences with those obta ined with the highest VPD. Photoperiod effects were not significant.