Abstract

This article presents results from a field research study conducted in the San Joaquin Valley of California between 2016 and 2018 to appraise the effects of soil salinity and sodicity on evapotranspiration and energy balance components of micro-irrigated commercial pistachio orchards. Actual evapotranspiration (ETa) and water-related tree physiologic parameters were measured during consecutive growing seasons in mature orchards grown on non-saline and saline/sodic soils. Salinity and sodicity decreased pistachio water use by about 30%, but the ETa reductions varied along the crop season. Accurate information on the dynamics of evapotranspiration and energy balance components along the crop season can inform better water management practices for nut orchards exposed to long-term saline-sodic conditions. Results show that the main driver of ETa is net radiation (Rn), which supplies most of the energy to vaporize water, irrespective of the growth period and the salinity/sodicity level. Field observations revealed that Rn was lower for salt-affected trees due to smaller canopies leading to less light interception. Secondarily, the exchange of sensible heat between the ambient air and tree canopies was affected by the interaction of salinity-sodicity and seasonality. Stem water potential measurements indicated that water stress limited ETa during June through August, whereas the leaf mineral contents revealed occurrence of ion specific toxicity that decreased ETa in September due to leaf burns. The results presented in this article provide insights to improve irrigation management of salt-affected pistachio through integration of weather measurements, energy balance components, and plant-based parameters.