Irrigation Timing of Three Landscape Shrubs Species Based on Foliage Tem-peratureRoger Kjelgren |
Changes in foliage temperature with vapor pressure deficit and water stress for three shrub species were investigated for use in irrigation scheduling in landscapes. Midday leaf-minus-air temperature (T l-T a) and vapor pressure deficit were monitored seasonally for prostrate juniper, upright juniper, and dwarf red-stem dogwood positioned as isolated plants or in a massed setting. There was an inverse baseline relationship between T l-T a and vapor 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 T l-T a 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 T l-T a over the baseline occurred more rapidly in isolated plants in both species. Foliage temperature readings of prostrate juniper were confounded a 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 T l-T a. This method will not work well for shrubs with sparse crowns and under shady, humid conditions. Supporting pdf: Irrigation Timing of Three Landscape Shrubs Species Based on Foliage Tem-perature |
