CO2 enrichment of greenhouse tomatoes using a closed-loop heat storage: Effects of cultivar and nitrogen

Spring crops of soil-grown greenhouse tomatoes (Lycopersion Lycopersicum (L.) Karst ex. Farw cultivars MO and TR-VE 23) were provided with three levels of nitrogen addition with and without added CO₂. Using a closed-loop solar collection/storage system, crops could be CO₂-enriched for 76–77% of the daylight hours. CO₂ enrichment increased No. 1 grade fruit weight by 14 and 27% and by 4 and 18% for both cultivars in 1981 and 1982, respectively. Although the method and amount of nitrogen application differed between 1981 and 1982, a trend was seen in both years for low nitrogen treatments to produce a greater response to CO₂ enrichment than high nitrogen treatments. A trend was also seen in both years for low nitrogen treatment to depress yield and quality in the non-enriched house, but to have no effect in the enriched house. This trend was particularly apparent in the cultivar with lower vegetative vigor, which also responded more overall to CO₂ enrichment than the cultivar with greater vegetative vigor.