BASIC PRINCIPLES OF ECONOMIC USE OF HEAT AND CO2 IN GREENHOUSE PRODUCTION
In optimizing input factors their effects on the plant (growth period or yield and timing, quality) as well as the costs have to be considered. Model calculations for lettuce and other vegetable crops have revealed the following:
figure 1: Referred to the same date of planting increased set points for temperature and CO2 - the same can be assumed for other growth enhancing factors - - have a large effect in accelerating growth and shortening the growth period, respectively, with autumn plantings, but a small one with winter-spring plantings.
figure 2: Referred to the same date of harvesting, increased set points for temperature and CO2 have a stronger effect in accelerating growth with winter-spring plantings, but a small one with autumn plantings.
figure 3: shows the growth curves for autumn and winter-spring plantings for a temperature set point of 12/18°C (day/night) and two CO2 concentrations (normal and 1000 ppm). These dates, obtained from seperate experiments, confirm the results of the model calculations in fig. 1 and 2. Further more they show, that the large effect of higher CO2 - concentration in autumn- referred to the same date of planting- can be explained by connecting the growth enhancing effect itself with avoiding the unfavourable growth conditions (here radiation) in winter. The effect of the increased CO2 - concentration applied to the same date of harvesting (hypothetical curve, estimated from the model exeeriments) is considerable smaller.