Estimation of the Amounts of Supplemental Carbon Dioxide (CO2) when Considering Night Respiration for a Hydroponics Tomato Greenhouse

Abstract

This study aimed to estimate amount of carbon dioxide (CO 2 ) supplementation necessary for tomato hydroponic cultivation by considering nighttime respiration using model-based equations. Experiment 1 was conducted in a commercial tomato hydroponic greenhouse during the spring growing season. Experiment 2 was conducted in an experimental greenhouse during the autumn growing season, with the predicted and measured CO 2 increases due to plant respiration during the nighttime also compared. In experiment 1, the supply rate of CO 2 fertilizer with LPG was a set to 600 µmol•mol -1 from 7:30 to 11:00 in a commercial tomato hydroponics greenhouse, and in experiment 2, CO 2 was supplied at a set rate of 600 µmol•mol -1 from 9:00 to 11:00 using a liquefied CO 2 generator in the experimental greenhouse. The estimation of the CO 2 concentration prior to the first supplement of the day was calculated by adding the CO 2 concentration about the time of sunset (lower than 50W solar radiation) on the last day to the integrated respiratory CO 2 concentrations during the nighttime. In experiment 1, the estimated amount of CO 2 supplement ranged from 3.24 to 36.9 g CO 2 •m -2 •h -1 when the nighttime temperature was between 16 and 19°C, while in experiment 2, the estimated amount of CO 2 supplement ranged from 4.21 to 52.6 g CO 2 •m -2 •h -1 when the lowest nighttime temperature was 13°C. These results suggest that the night respiratory CO 2 was affected by the night temperature of the greenhouse and therefore has an impact on the CO 2 supplementation amount. Therefore, it suggests that the new model equation that introduces night respiration into the estimation of supplemental CO 2 amounts can be used to precisely control greenhouse CO 2 supplement.