The Impact of Substrate and Irrigation Interval on the Post-Transplant Root Growth of Container-Grown Zinnia and Tomato

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Journal of Environmental Horticulture

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Substrate type and irrigation interval were studied to determine their impact on the post-transplant root growth of ‘Thumbelina' zinnia (Zinnis elegans Jacq.) and ‘Celebrity Hybrid' tomato (Lycopersicon esculentum Mill.). Seeds of both species were planted in 80 cm3 (2.7 fl oz) plug cells containing either Metromix 360™ (MM360) or Ball Professional Growing Mix™ (BPGM) and, following germination, the seedlings were transplanted into 450 cm3 (27.5 in3) plastic pots containing the same substrate. Evapotranspiration (ETO) was measured gravimetrically each day and the water lost via ETO added back to the substrate at intervals of 24, 48 or 96hr. For zinnia, root growth was consistently better for seedlings grown in BPGM, a substrate with greater water holding capacity and air-filled porosity. For plants grown in BPGM and irrigated every 48hr, root dry weight was significantly greater than it was for any of the remaining treatments. For tomato, root growth was greater for seedlings grown in BPGM and for transplants irrigated at 96 hr intervals; but, unlike zinnia, no significant interactions between substrate type and irrigation interval were observed. The results of this study show that root growth of plug-grown transplants can be improved by selecting a substrate with high porosity that allows for optimum oxygen and water exchange, and by extending the irrigation cycle to 48 hr (zinnia) or 96 hr (tomato).



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