Impact of Drought and Changing Water Sources on Water Use and Soil Salinity of Almond and Pistachio Orchards: 1. Observations

Abstract

Soil salinity increases when growers are forced to use higher salinity irrigation waters due to water shortages. It is necessary to estimate the impact of irrigation water on soil properties and conditions for crop growth to manage the effects of salinity on perennial crops. Therefore, in this study, we monitored root zone salinity in five almond and pistachio orchards in eastern and western San Joaquin Valley (SJV), California (CA). Volumetric soil water contents and bulk electrical conductivities were measured at four root-zone depths. Evapotranspiration was measured by eddy covariance along with three other types of data. The first is seasonal precipitation and irrigation patterns, including the temporal distribution of rains, irrigation events, and irrigation water salinity. The second is soil chemistry, including the initial sodium adsorption ratio (SAR) and soil solute electrical conductivity (ECe). The third type is the physical properties, including soil type, hydraulic conductivity, and bulk density. As expected, we found low salinity at the eastern sites and higher salinity at the western sites. The western sites have finer textured soils and lower quality irrigation water; measured actual ET was about 90% of modeled crop ET. Across the three western sites, the annual average apparent leaching fraction ranged from 11 to 28%. At the eastern sites, measured ET almost exactly matched modeled crop ET each year. Apparent leaching fractions in the eastern sites were approximately 20%.

Impact of Drought and Changing Water Sources on Water Use and Soil Salinity of Almond and Pistachio Orchards: 2. Modeling

“…Additionally, the soils at the ASM and PSH sites have a fine texture and high initial soil solution SAR. The high SAR reduced the soil hydraulic conductivity at both sites (as described in [31]). We believe that the lack of agreement between simulated and measured SWCs at the ASM and PSH sites (Figures 5 and 7) was caused by the previously discussed negative effects of soil SAR on the soil hydraulic conductivity.…”

“…The numerical model was calibrated for the five experimental sites. Soil water contents and soil salinities at depths of 25, 50, 75, and 100 cm measured during 2016-2018 (measurement methods are described in part 1 of this manuscript series [31]) were used in calibration. The model was validated using the third-year data sets from 2018 to 2019.…”

“…In part one of this manuscript series [31], we presented experimental data for several locations in the San Joaquin Valley (hereafter SJV), including precipitation, irrigation, ET fluxes, soil hydraulic properties, and measured root zone soil water contents and electrical conductivities. We also summarized seasonal averages and maximum values of root zone salinity.…”

“…In this second manuscript, we aim to use the experimental data from selected sites presented in part one [31] to (i) calibrate the HYDRUS-1D numerical model simulating transient root zone deep percolation, and plant water uptake, (ii) relate salt leaching fluxes and accumulated salt concentrations to soil properties, winter rainfall, and irrigation water quantity and quality, and (iii) establish base simulations of root zone salinity for two regions of the San Joaquin Valley (SJV), California. These base simulations and the calibrated model will then be used in a future part 3 of this manuscript series (Helalia et al, in prep.…”

“…Measured relative spatial distributions (the maximum is one) of root densities of almond trees (top) at the ASL (left) and ASH (right) sites and of pistachio trees (bottom) at the PSL (left) and PSH (right) sites. The terms "Tower" and "Outlying" refer to sampling locations with respect to the eddy covariance tower[31].…”