2017 ASHS Annual Conference

The objective was to evaluate whether injection of purified oxygen (oxygenation) of irrigation water to a super-saturated level affected plant growth during mist propagation of unrooted cuttings and subsequent growth in containers. The first factorial experiment aimed to measure the effect on rooting from two factors that included water type (“oxygenated” or “ambient” tap water) and plant species (Calibrachoa х hybrid ‘Aloha Kona Dark Red’ and Lobelia erinus ‘Bella Aqua’). The experimental design was a split-plot, randomized complete block where the main plot was a bench replicated four times, and the subplot was the water type. Within a water type there were two 51-count propagation trays (each tray was a replicate, 25-mm diameter cells) with plants from each of the two species. Dissolved oxygen measured at source tanks for oxygenated tap water (31.1 mg·L^-1) or ambient tap water (7.1 mg·L^-1) was pumped through fine mist nozzles (69 µm diameter). All plants were rooted by day 7 and growth continued to day 14. There were no measured differences in root length or root dry weight for Calibrachoa and Lobelia propagated using oxygenated water compared to ambient tap water, because all water that passed through fine mist nozzles reached 100% oxygen saturation (8.7 mg·L^-1) regardless of initial water type. The second factorial experiment measured the effect on rooting and plant growth from three factors including water type [“oxygenated” nutrient supplemented water (27.7 mg·L^-1) or “ambient” nutrient supplemented water (6.0 mg·L^-1)], irrigation delivery (“top-watered” or “subirrigation”), and plant species (Calibrachoa, Lobelia, and Pelargonium х hortorum ‘Patriot Red’). The experiment was a randomized complete block design with a total of four blocks (benches) and two replicate pots (10.2-cm diameter) per block for each combination of the three factors. Irrigation was standardized when substrate dried to approximately 45% of container capacity (CC), measured gravimetrically. A supplementary experiment also included Pelargonium grown at a high moisture level (80% CC) using subirrigation with the two water types. Oxygenated water did not enhance root or shoot growth in the second trial compared with ambient water for the three bedding plants at 45% CC, or with Pelargonium at the higher moisture level. Results emphasize that oxygenation of irrigation water is not likely to benefit plant growth in a container substrate, because (a) oxygen can off-gas when passed through small irrigation emitters, and (b) substrates can provide adequate air porosity if not kept saturated.