Hydrogel applied to the root plug of subtropical eucalypt seedlings halves transplant death following planting

Plantation establishment requires high survival of transplanted seedlings. The experiments described in this paper examined methods to reduce death of Eucalyptus pilularis Smith and Corymbia citriodora subsp. variegata (F. Muell.) A.R. Bean & M.W. McDonald seedlings shortly after planting. Two products were tested: a fine grade water-retention hydrogel was examined as a means of providing water to seedlings, and a kaolin clay particle film mixture sprayed onto leaves was examined as a means of reducing leaf heating and dehydration. Both products were tested in a field and a glasshouse situation. Seedlings were planted with a pottiputki for field experiments or a hand trowel for glasshouse experiments. Seedlings were not watered in the glasshouse trial. Hydrogel was applied by immersing the seedlings’ root plug in a fully hydrated solution of hydrogel prior to planting which supplied each seedling with an additional 20 g weight corresponding to 20 ml of water. Kaolin clay particle film was applied by coating the leaves prior to planting. Field trials showed the majority of seedling death occurred between 1 and 4 weeks after planting with seedling health improving during this period following rainfall events. Five months after planting in the field hydrogel-treated seedlings had 12 and 5% death in E. pilularis and C. citriodora subsp. variegata seedlings compared to 26 and 14% death, respectively in control seedlings. The glasshouse trial showed hydrogel-treated seedlings remained healthier for longer. Hydrogel enhanced seedling survival because it provided extra moisture to seedlings, or it promoted contact between the root plug and the bulk soil. Kaolin clay particle film showed a non-significant trend of improving survival of field planted seedlings. There was also a non-significant trend indicating that kaolin clay delayed death of C. citriodora subsp. variegata seedlings when time between application and planting was increased. Species attributes such as presence of lignotubers and smaller leaf area in C. citriodora subsp. variegata than E. pilularis may account for its higher survival, although seedling morphology could not easily be related to seedling survival.