The effect of intracanopy lighting on cucumber fruit yield-Model analysis

Abstract Intracanopy lighting is a recently developed supplementary lighting technique for high-wire grown vegetable production in greenhouses where a part of the lamps is mounted within instead of above the canopy. A potentially higher yield using intracanopy lighting compared with top-lighting, is based on three assumptions: (1) increased light-absorption by the crop; (2) a higher photosynthetic light use efficiency due to a more homogeneous vertical light distribution; (3) a preserved photosynthetic capacity of leaves deeper in the canopy. We used an explanatory crop model to quantify the relative importance of these assumptions for a cucumber crop during an experiment in winter in the Netherlands ( Trouwborst et al., 2010 ). Photosynthesis and yield data of this intracanopy lighting experiment with light-emitting diodes (34% of supplemental PAR) in combination with top-lighting (66% of supplemental PAR) were used to parameterise our model. In that study intracanopy lighting did not result in an increased yield compared with 100% top-lighting due to extreme leaf curling and a lower dry matter partitioning to the fruits. Our model predicted an 8% increase in fruit yield for the intracanopy lighting treatment if there were to be no leaf curling and no lower dry matter partitioning. This increase can be largely explained by the change in light distribution and light absorption. The model further revealed unexpectedly large consequences of the lower dry matter partitioning to the fruits whereas the negative effect of leaf curling was small. The direct effect of a greater Amax at deeper canopy layers was slightly positive. The last however might have indirectly caused the greater partitioning to the leaves as the greater Amax was associated with a preserved leaf mass per area. Solutions for this problem are discussed. Our explanatory model allowed us to disentangle the interacting effects of intracanopy lighting on fruit yield. Overall, intracanopy lighting has been shown here to potentially increase the assimilation light use efficiency.

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