Post-transplant Water Utilization of Zinnia Seedlings Grown in Humectant-amended Substrate Maintained at Two Moisture Thresholds1

Abstract

Humectant treatment and substrate moisture content (SMC) were studied to determine their impact on post-transplant water utilization in ‘Thumbelina' zinnia (Zinnia elegans Jacq.). Four-week-old seedlings were transplanted from plug trays into pots containing soilless substrate amended with an aqueous solution of 1.6% Hydretain® or an equal volume of water (0% humectant). Seedlings were placed in an automated, sensor-controlled irrigation system and grown for 30 days at SMC levels of 0.45 or 0.25 cm3·cm−3 (0.06 or 0.03 fl oz·oz−1). Plant-water potential (Ψw) was significantly higher (less negative) in transplants grown in humectant-treated substrate at both SMC levels, and water-use efficiency (WUE) was 2X greater for seedlings grown in treated substrate maintained at 0.25 cm3·cm−3 than it was for transplants grown in untreated substrate at the same SMC level. No significant differences in height, stem diameter or shoot dry weight were observed when comparing plants grown in treated and untreated substrate. Root dry weight was significantly greater for seedlings grown in untreated substrate. Flowering was not affected by humectant treatment or by SMC. The results show that transplanted zinnia ‘Thumbelina' seedlings require less irrigation when grown at a lower SMC threshold in soilless substrate amended with 1.6% Hydretain®. Index words: automated irrigation control, cultural practices, plant-water relations, transplant establishment, water management, water-use efficiency. Species used in this study: ‘Thumbelina' zinnia (Zinnia elegans Jacq.). Chemicals used in this study: Hydretain® - a proprietary blend of sugar alcohols, polysaccharides, and neutral salts of alphahydroxyproprionic acid.