IMPROVING IRRIGATION SCHEDULING PROTOCOLS FOR NURSERY TREES BY RELATING CUMULATIVE WATER POTENTIAL TO CONCURRENT VAPOUR PRESSURE DEFICIT^©

Conventional irrigation practices are based on physical factors and observations, however this fails to include plant water status measurements. This study examined the relationship between cumulative water potential with concurrent cumulative vapour pressure deficit (VPD) for the common nursery species Thuja occidentalis ‘Smaragd’ (emerald pyramidal cedar). Establishing the relationship for these plant-environment interactions will provide nursery growers with a rational irrigation scheduling tool that indicates a more effective and efficient use of scarce water resources. Plant water status and environmental conditions were monitored throughout a growing season taking measurements every 15 min between irrigation events. The overall relationship between cumulative water potential and cumulative VPD exhibited a slope response of -2.2 MPa·h/kPa·h. This coefficient provides growers with an objective tool for irrigation management for this species and leads the way to exploit this approach across the spectrum of nursery commodities.