California Agriculture

Using tree water status measurements in orchard irrigation management is predicated on the fact that these values are closely linked to important physiological processes, such as growth. In our study, stem water potential (SWP) was highly correlated with vegetative growth in almond trees. However, the SWP technique requires that leaves be covered by small, foil-covered plastic bags for a certain time prior to the pressure chamber measurement and that the atmospheric vapor pressure deficit (VPD) in the orchard be considered in interpreting the data. This can be time consuming and labor intensive for growers. Growers need alternative approaches for taking pressure chamber measurements that are rapid, simple and easy to interpret. We found that measurements of shaded leaf water potential (LWP), taken when the leaf was covered by a damp cloth for the short time between leaf excision and placement in the pressure chamber, correlated well with SWP. Moreover, air temperature at the time of measurement was as useful as VPD for interpreting shaded LWP as an indicator in irrigation management. In addition to weather, this work identified operator differences as a major source of variation in water potential measurements. Plant-based measurements can be useful tools if precautions are taken concerning variability. Shaded LWP has logistical advantages over SWP and this study suggests that it can be used without sacrificing accuracy.