Irrigation timing of tree landscape shrub species based on foliage temperature

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Arboricultural Journal: The International Journal of Urban Forestry






Taylor & Francis

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Changes in foliage temperature with vapour pressure deficit and water stress for three shrub species were investigated for use in irrigation scheduling in landscapes. Midday leaf-minus-air temperature (T1-Ta) and vapour pressure deficit were monitored seasonally for prostrate juniper (Juniperus horizontalis ‘Wiltonii’), upright juniper (J. chinensis ‘Hetzi’, and dwarf red-stem dogwood (Cornus sericea ‘Kelseyii’), positioned as isolated plants or in a massed setting. There was an inverse baseline relationship between T1-Taand vapour pressure deficit for all species and both spacings under well-watered conditions. This was consistent with baselines reported for herbaceous crops, but with substantially more scatter. Baseline relationships between spacings were similar for upright juniper and dogwood, but not for prostrate juniper. During a dry-down cycle T1-Ta exceeded the well-watered baseline for dogwood and upright juniper, signalling incipient water stress. Stress was confirmed in declining predawn leaf water potential and water content of the container media. Due to more water loss, increases in T1-Ta over the baseline occurred more rapidly in isolated plants in both species. Foliage temperature readings of prostrate juniper were confounded by sparse canopy that transmitted background radiation. These results suggest that irrigation of certain shrubs in a landscape with dense canopies can be timed to increases in T1-Ta. This method will not work well for shrubs with sparse crowns and under shady, humid conditions.

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