Irrigation Scheduling Based on Cumulative Vapour Pressure Deficit to Predict Nursery Tree Water Stress
Ontario tree nurseries are among the heaviest users of irrigation water in the ornamental horticulture sector. Increasing concerns with water conservation, environmental impacts and costs have encouraged the nursery industry to modify its water use, however an effective irrigation management strategy remains elusive. Conventional irrigation scheduling for nursery trees is often based on subjective observations and field experience, which excludes plant water status measurements. Using field-deployable stem psychrometers paired with conventional meteorological measurements, the aim for this thesis was to quantify the relationship between cumulative water potential (CWP) and concurrent cumulative vapour pressure deficit (CVPD) to develop an irrigation scheduling technique which predicts plant water status responses from environmental variables, specifically vapour pressure deficit (VPD). This relationship yielded average slope responses for Thuja occidentalis (L.) of -2.4 MPaHrs / kPaHrs and for Acer rubrum (L.), -1.5 MPaHrs / kPaHrs. The CWP/CVPD relationship needs further refinement for irrigation management strategies in a broader selection of nursery trees.