High pH, Low Alkalinity Pond Water Used for Overhead Irrigation Does Not Affect Plant Growth of Select Flowering Shrubs1

In southeast U.S., pH of source water from ponds used for overhead-irrigating container crops can exceed the range (pH 5.8-7.0) for best management practices. Artificially maintaining this pH range is not common among producers using surface water for irrigation, nor is it known whether this would affect growth. Therefore, the objective was to test whether this source water affects growth of five flowering shrubs in nurseries in eastern North Carolina. Pond water at six nurseries with a pH range of 4.9-8.1 (control) was injected before irrigation with sulfuric acid (lower) or potassium bicarbonate (raise) onsite to maintain a pH of 5.8-6.2 (treatment). Ambient photosynthesis (Aambient) and stomatal conductance (gs) was measured in July, August, and September on leaves of forsythia (Forsythia x intermedia 'Mindor‘ ShowOff®) during irrigation runtime mini-experiments at three nurseries. For mini-experiments, pre- and post-treatment physiology was measured for plants receiving 0 (hand watered), 30, or 60 minutes of treated or nontreated overhead irrigation. Dry weight of all shrubs and gas exchange of forsythia was not affected by high pH, low alkalinity (<100 ppm) irrigation water. Southeastern producers using this source water for overhead irrigation may not need to adopt a system that reduces pH to improve growth. Index words:, Container-grown, plant physiology, photosynthesis, stomatal conductance, ornamental. Chemicals used in this study: Potassium bicarbonate, sulfuric acid. Species used in this study: fragrant abelia, Zabelia tyaihyonii (Nakai) Hisauti & H.Hara 'SMNAMDS‘ Sweet Emotion®; butterfly bush, Buddleia x ‘Miss Molly'; border forsythia, Forsythia x intermedia ‘Mindor‘ Show Off®; panicled hydrangea, Hydrangea paniculata Siebold ‘SMHPLQF' Little Quick Fire®; landscape rose, Rosa x ‘ChewPatout' Oso Easy®.