An assessment of potato sap flow as affected by soil water status, solar radiation and vapour pressure deficit

Water-use of three field-grown potato cultivars (Atlantic, Monona and Norch ip) was examined using a commercially available sap flow monitoring system over three consecutive growing seasons. The objectives of the investigation were to utilize the sap flow system to assess the water use of three field -grown potato cultivars. This included an assessment of the relationship be tween environmental conditions, water status and measured sap flow includin g the plant-to-plant variation in sap flow and an evaluation of relative tr anspiration in relation to the soil water status. Each cultivar maintained daily sap flow close to the atmospheric potential transpiration until approximately 70% of the available water was depleted. Under conditions where the soil was drier (>70% depleted), Monona potato pl ants exhibited a more rapid decline in transpiration than Norchip and Atlan tic. Hourly sap flow rates were closely related to solar irradiance, especially under well-watered conditions, with no apparent light saturation point. Vap our pressure deficit effects on sap flow were less pronounced, although max imum vapour pressure deficits encountered were only 2 kPa.