Optimizing photosynthesis via high-pressure fogging and data-driven research

A high-pressure fogging trial was conducted in two identical compartments in a 16-hectare bell-pepper greenhouse in Canada. One compartment had high-pressure fogging, while the other did not. With this setup, LetsGrow.com and MJ-Tech last year embarked on a collaborative project. The team sought to understand the optimal use of high-pressure fogging to improve production quality, and yield, as well as reduce operational expenses. All that was driven by data-based decisions, of course. Their complete findings are shared in a whitepaper, and we are here to talk you through the highlights.

High-pressure fogging active at a bell pepper greenhouse in Canada, the facility where the discussed trial took place.

Biological foundation and key terms
"Photosynthesis, the process by which plants convert CO2 and H2O into assimilates and oxygen using light, is central to plant growth. Optimizing photosynthesis involves balancing temperature, CO2, and humidity with incoming light. Temperature influences enzymatic activities, CO2 affects the rate of photosynthesis, and relative humidity (RH) regulates stomata behavior, which in turn controls gas exchange and water loss through transpiration," Rob Kwinten of MJ-Tech explains. Alexandra Skouria and Evripidis Papadopoulos of LetsGrow.com added; "Monitoring and maintaining these factors can be complex and time-consuming, prompting the creation of the climate monitor tool by LetsGrow.com. This tool sets desired climate conditions relative to light levels, ensuring that plants remain in balance to maximize production and quality."

Climate monitor example as shown at LetsGrow.com. Green vertical bars show the percentage of climate in balance. Climate parameters are shown with different color lines, radiation (W/m2) (yellow), temperature greenhouse (°C) (red), relative humidity of the greenhouse (%) (blue), and CO2 (ppm) (black).

High-Pressure fogging system
High-pressure fogging involves injecting 3–5-micron water droplets into the air to increase humidity and lower temperatures while maintaining constant enthalpy levels. This promotes stomata opening, essential for CO2 uptake and photosynthesis, and enhances transpiration, crucial for nutrient transport and water balance in plants. The system's effectiveness depends on precise control to ensure water droplets evaporate before reaching the plants, reducing fungal risk. Sensors monitor various parameters to adjust fogging accurately across different seasons and climate conditions.

Trial design and methodology
The trial in Ontario involved two identical greenhouse compartments growing bell peppers. One compartment utilized MJ-Tech's high-pressure fogging system controlled by the IIVO greenhouse control system of Hoogendoorn Growth Management, while the other did not. The goal was to assess the impact of misting on temperature, humidity, and CO2 levels. "The fogging system significantly lowered the temperature in the misting compartment by an average of 1.9°C and increased RH by 9.2%. It also maintained an optimal Vapor Pressure Difference (VPDifference), ensuring optimal stomata opening, hence transpiration and plant growth."

Furthermore, "Reduced ventilation during fogging led to higher CO2 levels, enhancing photosynthesis," Rob shows. "High-pressure fogging effectively creates optimal microclimate by regulating temperature and humidity, thereby enhancing photosynthesis and transpiration. This system can be particularly beneficial in hot and dry conditions, reducing plant stress and improving growth and yield. Proper setpoints for different growth stages are crucial to avoid over-humidification and ensure robust root development."

Relative humidity difference between compartments 1 (no misting) and 3 (misting) during April and October 2023. Dark blue colors indicate that compartment 3 had a higher humidity by 2-10% compared to compartment 1. The graph was produced using the strategy scan tool by LetsGrow.com.

Future Directions
The initial trial's insights functioned as a base to the second research cycle, which started in January 2024, aiming to further refine the system operations for maximum benefit. This will involve developing tailored strategies using intelligent algorithms, focusing on advanced ventilation and other climate control aspects. Once completed, a second part of the whitepaper will be published with these results as well.

Click here or here for the complete research and whitepaper, or find it at the Letsgrow site.