S06 - Session P7 - Toplight versus partial intercanopy light with white LEDs in greenhouse cucumber and tomato at two light intensities

Authors: Ep Heuvelink *, Tijmen Kerstens, Theodoros Gianneas, David Hawley, João Ludovico, Sebastian Olschowski, Theoharis Ouzounis, Ingeborg Schouten, Leo F.M. Marcelis

This research aims at comparing supplemental light using white LEDs provided on top of the crop (toplight) or provided partly on top and partly as intercanopy light (ICL) in a high-wire cucumber and tomato crop. For each crop three replicate Venlo glasshouse compartments were used. Two cucumber and two tomato cultivars were planted in the second half of October 2020 and grown on stone wool for a period of 15 or 20 weeks, respectively. Supplemental white LED light was supplied at either a total light intensity of 250 or 375 µmol m -2 s -1 , provided either as 100% toplight or as 67% toplight and 33% ICL. Each glasshouse compartment consisted of four sub-compartments in which the four light treatments were allocated, and within each sub-compartment the two cultivars were grown. For cucumber at the higher light intensity more fruits were retained and for tomato at the higher light intensity plant density was higher to keep the plants balanced in terms of source to sink ratio. Replacing 33% of toplight with ICL resulted on average in an increase of 17% in fresh fruit yield for both cucumber and tomato. This increase was larger at the higher light intensity than at the lower light intensity. For cucumber higher yield for ICL treatments resulted from higher total plant dry weight and higher fraction of dry weight partitioned to the fruits. ICL increased photosynthesis rate of leaves in the middle of the canopy. For tomato, total plant dry weight was higher when ICL was applied whereas dry weight partitioning over the different plant organs was not affected by ICL. ICL resulted in higher maximum photosynthetic rates for leaves low in the canopy. For cucumber 33% ICL compared to 100% toplight resulted in longer greener fruits, whereas tomato fruit quality (Brix, pH) was not affected by ICL.