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

Sarah A Helalia,Jirka Šimůnek,Todd H Skaggs,Ray G Anderson

doi:10.3390/soilsystems5040058

Sarah A Helalia, Jirka Šimůnek + Show 2 more

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https://doi.org/10.3390/soilsystems5040058

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Abstract

California is increasingly experiencing drought conditions that restrict irrigation deliveries to perennial nut crops such as almonds and pistachios. During drought, poorer quality groundwater is often used to maintain these crops, but this use often results in secondary salinization that requires skilled management. Process-based models can help improve management guidelines under these challenging circumstances. The main objective of this work was to assess seasonal soil salinity and root water uptake as a function of irrigation water salinity and annual rain amounts. The manuscript presents a comparison of three-year experimental and numerically simulated root zone salinities in and below the root zone of almond and pistachio drip-irrigated orchards at multiple locations in the San Joaquin Valley (SJV), California, with different meteorological characteristics. The HYDRUS-1D numerical model was calibrated and validated using field measurements of soil water contents and soil solute bulk electrical conductivities at four root zone depths and measured soil hydraulic conductivities. The remaining soil hydraulic parameters were estimated inversely. Observations and simulations showed that the effects of rain on root zone salinity were higher in fields with initially low salinities than in fields with high salinities. The maximum reduction in simulated root water uptake (7%) occurred in response to initially high soil salinity conditions and saline irrigation water. The minimum reduction in simulated water uptake (2.5%) occurred in response to initially low soil salinity conditions and a wet rain year. Simulated water uptake reductions and leaching fractions varied at early and late times of the growing season, depending on irrigation water salinity. Root water uptake reduction was highly correlated with the cumulative effects of using saline waters in prior years, more than salt leaching during a particular season, even when rain was sufficient to leach salts during a wet year.

Highlights

California’s agricultural management practices need to be adjusted to account for ongoing water scarcity and forecasted climate change
In part one of this manuscript series [31], we presented experimental data for several locations in the San Joaquin Valley, including precipitation, irrigation, ET fluxes, soil hydraulic properties, and measured root zone soil water contents and electrical conductivities
The HYDRUS-1D simulated and measured soil water contents (SWCs) showed suitable agreement, both exhibiting time courses that corresponded to rain and irrigation inputs (Figure 2)

Summary

Introduction

California’s agricultural management practices need to be adjusted to account for ongoing water scarcity and forecasted climate change. Numerical models have proven to be valuable and efficient tools for carrying out spatial-temporal agricultural system analyses aimed at enhancing productivity under various irrigation schemes and assessing ongoing climate change effects on soil salinity [4,5,6,7]. Soil salinity problems integrate the effects of many time-varying factors, including soil properties, climate, crops, irrigation methods, and management practices. Transient models can provide solutions for quantifying salinity build-up in the root zone due to these various processes and factors. These may include irrigation-induced salinity, upward movement of salts from the saline groundwater table, and sodification processes [9]

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