OPTIMIZATION OF CO2 CONCENTRATION IN GREENHOUSES - A MODELING ANALYSIS FOR THE LETTUCE CROP

The dependence of photosynthesis of crops on light irradiance and CO2 concentration are reviewed. A two-dimensional representation of a lettuce crop is developed into a form suitable for maximizing grower income by enhancing CO2 concentration. Analytical relationships for the optimal CO2 concentration are set up for a commercial lettuce crop and solved. Optimal concentrations are shown to depend linearly on irradiance levels, and on the square root of the inverse of the ventilation rate and on the ratio of lettuce price to CO2 cost/kg. Using hourly values of incident radiation measured at Cardington, Bedfordshire, ventilation rates are predicted and optimal CO2 concentrations obtained. Optimal incomes so produced are compared with those for fixed CO2 enhancement levels under the same ambient conditions. Results indicate that a corresponding improvement of 10% in income is possible, though verification using measured greenhouse parameters is required. © 1991 The British Society for Research in Agricultural Engineering.