Abstract

Water-absorbing polymers (hydrogels) are promoted for their potential to increase the water-holding capacity of container media. European birch (Betula pendula Roth) seedlings (1 + 0 plugs) were planted in a container growth medium amended with 0, 1.2, 2.4 or 3.6 kg/m³ (0, 2, 4 or 6 lb/yd³) of Broadleaf P-4, a commercial hydrogel, and watered either daily or once every 3 or 5 days. When hydrogel was incorporated in the growth medium, shoot and root dry weights and leaf area were reduced by 19, 29 and 18%, respectively, compared to controls. Increases in stem height and diameter as well as shoot-root ratio were unaffected by hydrogel amendment rate. Compared to seedlings in polymer-amended media, plants growing in medium without hydrogel had significantly lower stomatal conductance and transpiration on fewer than 25% of the measurement dates. Irrigation frequency significantly affected all plant growth indices and stomatal parameters; seedlings irrigated daily grew the most and had the highest stomatal conductance and transpiration. Although polymer-amended media held more water than medium without hydrogel at all measured tensions, this moisture was retained in the expanded gel rather than being available for plant uptake at higher tensions. The hydrogel appeared to have little benefit for container production of birch.