Maximum daily trunk shrinkage sensitivity to water use of pistachio under saline conditions

Plant based methods could allow more accurate irrigation management of crops grown under water restrictions, which is often associated with the use of poor-quality water. However, little information is currently available about the use of plant-based-methods for crop irrigation management under saline conditions. This study evaluates the reliability of maximum daily trunk shrinkage (MDS) for irrigation management of pistachio under saline-sodic conditions. Trunk diameter variations were monitored in a non-saline orchard and in a saline-sodic orchard located in the San Joaquin Valley (CA). Daily actual evapotranspiration (ETa) was determined using the residual of energy. Stem water potential (Ψstem) was also measured weekly to characterize the plant water status. Early in the season, MDS showed relatively higher correlation to ETa in the saline-sodic orchard with a correlation coefficient (r) of 0.65. In the same period, the tree trunks were actively growing and the salt-affected trees showed higher MDS values and lower Ψstem values with respect to the non-saline orchard. This suggests that lower soil osmotic potential of saline soils may be limiting water uptake during this stage. Differences in water use, however, between the saline and non-saline orchards were low (~1.2 mm day^-1). Late in the season, MDS was not well correlated to ETa, showing a correlation coefficient around 0.3. During this period there was a lack of trunk growth in both non saline and saline trees. A decrease in MDS, and an increase in Ψstem values were recorded in the salt-affected trees. A higher water use difference was measured (~2 mm day^-1) between the saline and non-saline orchards late in the season. Overall, this study suggests that the effects of salinity on pistachio water use are dynamic during the crop season, hence more than one indicator may be necessary to enhance irrigation management of salt-affected orchards.