Impact of drought and changing water sources on water use and soil salinity of almond and pistachio orchards: 1. Observations

Authors: HELALIA, SARAH - University Of California; Anderson, Raymond - Ray; Skaggs, Todd; JENERETTE, DARREL - University Of California; Wang, Dong; ŠIMUNEK, JIRKA - University Of California

Submitted to: Soil Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2021
Publication Date: 8/25/2021
Citation: Helalia, S.A., Anderson, R.G., Skaggs, T.H., Jenerette, D., Wang, D., Šimunek, J. 2021. Impact of drought and changing water sources on water use and soil salinity of almond and pistachio orchards: 1. Observations. Soil Systems. 5(3). Article 50. https://doi.org/10.3390/soilsystems5030050.
DOI: https://doi.org/10.3390/soilsystems5030050

Interpretive Summary: Recent drought in California has forced growers of perennial nut crops to pump groundwater for irrigation when surface supplies are insufficient. This use of groundwater not only unsustainably depletes groundwater reserves, but it also contributes to soil salinization and negative impacts on tree health and yield due to the poorer quality of groundwater found in many tree nut growing regions such as the Western San Joaquin Valley. To understand how changing irrigation water sources impacts established commercial orchards, we conducted an observational and modeling study across five almond and pistachio orchards in the San Joaquin Valley across a gradient of soil salinity and irrigation with different water sources. In the first part of this study, we report the observational data from soil moisture sensors and eddy covariance instrumentation. Observations of soil salinity showed expected seasonal trends in the Western San Joaquin Valley, with increases in the summer and fall. Crop water use was more stable and closer to meteorological demand for the lower salinity pistachio and almond orchards in the Eastern San Joaquin Valley, thus suggesting that they were less stressed than the higher salinity orchards in the Western San Joaquin Valley. The study results emphasize the need to consider irrigation water quality in drought mitigation plans and to minimize the use of lower quality water sources during drought periods for salt sensitive crops. This information will be of interest to farmers, irrigation managers, and policymakers, especially those involved with Groundwater Sustainability Agencies.

Technical 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%.