Carbon Dioxide Enrichment May Increase Yield of Field-grown Red Raspberry under High Tunnels

Abstract

The objectives of this preliminary study were to optimize a carbon dioxide (CO 2 ) application system for field-grown raspberry ( Rubus ideaus ) under high tunnels and then to compare plant photosynthesis, growth, and fruit yield with and without CO 2 . Based on plant photosynthesis measures before CO 2 application, we placed the drip irrigation tape to apply CO 2 in the middle of the plant canopy at 100 cm aboveground and split daily CO 2 application from 0700 to 1100 hr and 1400 to 1800 hr . In the morning hours, CO 2 concentration in the tunnel was 18% higher than in the afternoon; wind speed often increased later in the day, which may have moved the CO 2 even in the tunnel. We maintained an average CO 2 concentration of 436 ppm for 4 months, applying about 25 tons of CO 2 . In tunnels enriched with CO 2 , yield and berry size from plots 20 ft in length increased 12% and 5%, respectively, compared with untreated tunnels. We measured no corresponding differential response in the number of 6-oz baskets harvested from the full tunnel, leaf CO 2 assimilation, stomatal conductance ( g S ), or fluorescence, raspberry cane height, pruned cane biomass, cane diameter, or carbohydrate content of the fruit after CO 2 application. Documenting potential plant physiological changes should therefore be a focus of future research.