Interlighting improves production of year-round cucumber

Three cucumber stands (Cucumis sativus L. cv. Cumuli) were grown in southern Finland to investigate the effects of two supplemental lighting regimes on yield and efficiency of electricity consumption in lighting for year-round production. The lighting regimes examined included top lighting (TL), where all of the lamps were mounted above the canopy and top + interlighting (T + IL) which comprised 75% of top lamps and 25% of the lamps mounted vertically 1.3 m above the ground between the single plant rows. The artificial photosynthetic photon flux (PPF) near the plant rows, the air temperature and vapour pressure deficit (VPD) in the canopy were noted to be slightly higher in T + IL than in TL. The total (natural + artificial) PPF inside the greenhouse during cultivation of the winter, spring and summer stands were 19.4, 29.5 and 38.6 mol m(-2) day(-1) in TL and 20.4, 31.5 and 41.2 mol m(-2) day(-1) in T + IL, respectively. Top + interlighting was shown to enhance cucumber productivity; T + IL increased the annual total and first class fruit weight and number, fruit size and percentage of first class fruit. A total annual increase of 20% in first class fruit weight was achieved through a 6% increase in electricity consumption for lighting purposes. The first class fruit weights in winter, spring and summer stands were 32.0, 42.1 and 30.8 kg m(-2) in TL and 38.2, 55.4 and 32.1 kg m(-2) in T + IL, respectively. The efficiency of electricity consumption for lighting was better for the whole year in T + IL than in TL (120 g versus 108 g first class fruit weight kWh(-1)). Efficiency varied between stands; T + IL proved more efficient than TL during the winter and spring seasons, whereas TL was more efficient in summer. (C) 2004 Elsevier B.V. All rights reserved.