THE INFLUENCE OF SUPPLEMENTARY ILLUMINATION AND CO2 ENRICHMENT ON THE GROWTH, FLOWERING AND FRUITING OF THE TOMATO
Height to the first truss was increased by both the light and CO2 treatments, but subsequent intertruss distances were reduced resulting in a highly significant reduction in height to the seventh truss. There was no significant difference in leaf numbers to the first truss, but light treatment reduced the leaf number between the first and second truss from 4.62 to 3.04 (p<0.001).
CO2 enrichment advanced flowering of the first inflorescence by 2.38 days (p<0.05), supplementary light by 14.02 days (p<0.001) and the combination treatment by 17.64 days. The trends were somewhat similar up to the tenth truss where supplementary light during propagation advanced flowering by 8.83 days.
Light increased total flower numbers on the first 9 inflorescence by 6.8% (p<0.005), CO2 enrichment by 9.3% (p<0.01) and the combination by 14.4% (p<0.001). Fruit numbers on the first 8 trusses were increased by 12.4% (p<0.001) and 19.0% (p<0.001) by the CO2 and light-CO2 treatments respectively. Fruit numbers on the first truss, however, were reduced 31.4% where light alone was used, but increased slightly with CO2 enrichment.
CO2 enrichment increased early yields (to May 15) by 1.50 tons/acre (3613 kg/ha), supplementary light by 6.39 tons/acre (15392 kg/ha) and the combination treatment by 10.22 tons/acre (24617 kg/ha). Mid-season yields (to June 15) were increased 1.56 tons/acre (3758 kg/ha) with CO2 10.89 tons/acre (26231 kg/ha) with light and 17.04 tons/acre (41046 kg/ha) with the combination of both. Total yields (to July 17) were increased by 10.51, 8.52 and 23.68 tons/acre (25316, 20523 and 57040 kg/ha) with CO2, light and the combination treatment respectively.
After allowing for the total annual running costs of treatments it was found that CO2 enrichment increased gross returns by £1,917 per acre (ƒ4733/ha), supplementary illumination by £2,723 (ƒ6723) and the combination treatment by £6,082 (ƒ15,017). On the basis of these results it is suggested that supplementary illumination is a more economic proposition than CO2 enrichment.