Evaluation of the effects of supplemental lighting and stem number on greenhouse sweet pepper growth and yield via ray-tracing simulation with 3D plant models

In greenhouses, sweet peppers with adequate stem density can improve fruit yield. However, a higher number of stems may negatively affect growth and fruit yield due to higher fruit load and lower light interception. For this reason, supplemental lighting has widely been applied to greenhouse cultivation, but it is not easy to analyse its effect due to the high spatial complexity of canopy components. This study aimed to analyse the growth and yield of sweet pepper plants with different stem densities under supplemental lighting and to evaluate the canopy light profile and photosynthesis using ray-tracing simulation with 3D plant models. Supplemental lighting using high-pressure sodium lamps (SL) started from December 1, 2020, to May 25, 2021. 3D plant models were constructed using a 3D scanner at 13 and 20 weeks after transplanting. Crop photosynthesis was calculated from simulated light interception using the modified FvCB model. Under SL, the dry weight of plants and the total fruit yields per plant were significantly higher than under natural light (NL). The 3D analysis enabled us to accurately estimate the light interception and photosynthetic rate of the two and three stem plants. The simulation results showed that the total photosynthetic assimilation was improved under SL, resulting in improved fruit production. With simulated canopy light profiles in the greenhouse, annual operation costs and energy consumption for fruit yields of the plants with different stem densities could be estimated. This method could help determine stem density and supplemental lighting levels during crop cultivation in greenhouses. (c) 2023 IAgrE. Published by Elsevier Ltd. All rights reserved.