Precise 3D evaluation of light microclimate for summer production in insulated plastic greenhouses

Solar greenhouses are energy-efficient facilities for year-round crop production. To better understand the effects of shading caused by the insulation quilts on the microclimate and canopy light interception, this study systematically investigated summer cucumber production inside an insulated plastic greenhouse in Beijing, China. Monitoring experiments were conducted across the seedling, flowering, fruiting, and maturity stages, and were combined with 3D simulation modeling. Specifically, the radiation transmittance of greenhouse roof was analyzed at different solar altitude angles. A functional-structural plant model (FSPM) was employed to evaluate the spatiotemporal distribution of light within the greenhouse. Shaded areas resulting from the insulation quilts were calculated, and the daily light integral (DLI) on the canopy under various shading patterns was quantified. Results showed that insulation quilt shading reduced indoor temperature by an average of 4.2 °C and increased relative humidity by 7.5 %, but also caused a significant reduction in canopy light availability. The average DLI during the seedling, flowering, fruiting, and maturity stages was merely 9.1, 10.8, 16.8 and 20.8 mol/m2/d, respectively, which was significantly lower than the commonly recommended range of 20–30 mol/m2/d for optimal growth. Considering the combined effects of temperature, humidity and photosynthetic requirements, supplementary lighting at night is necessary to ensure optimal crop development. The modeling framework proposed in this study represents an initial step toward quantitatively evaluating shading effects in greenhouse. This approach is not constrained by geographic location and can be directly applied to other greenhouse types and crop species.