Abstract
Treated wastewater irrigation began two decades ago in the Salinas Valley of California and provides a unique opportunity to evaluate the long-term effects of this strategy on soil salinization. We used data from a long-term field experiment that included application of a range of blended water salinity on vegetables, strawberries and artichoke crops using surface and pressurized irrigation systems to calibrate and validate a root zone salinity model. We first applied the method of Morris to screen model parameters that have negligible influence on the output (soil‐water electrical conductivity (ECsw)), and then the variance-based method of Sobol to select parameter values and complete model calibration and validation. While model simulations successfully captured long-term trends in soil salinity, model predictions underestimated ECsw for high ECsw samples. The model prediction error for the validation case ranged from 2.6% to 39%. The degree of soil salinization due to continuous application of water with electrical conductivity (ECw) of 0.57 dS/m to 1.76 dS/m depends on multiple factors; ECw and actual crop evapotranspiration had a positive effect on ECsw, while rainfall amounts and fallow had a negative effect. A 50-year simulation indicated that soil water equilibrium (ECsw ≤ 2dS/m, the initial ECsw) was reached after 8 to 14 years for vegetable crops irrigated with ECw of 0.95 to 1.76. Annual salt output loads for the 50-year simulation with runoff was a magnitude greater (from 305 to 1028 kg/ha/year) than that in deep percolation (up to 64 kg/ha/year). However, for all sites throughout the 50-year simulation, seasonal root zone salinity (saturated paste extract) did not exceed thresholds for salt tolerance for the selected crop rotations for the range of blended applied water salinities.
Highlights
Salinization of soils, groundwater, and surface waters from irrigation is a well-known problem often associated with the decline of ancient civilizations dependent on irrigated agriculture around the world, such as Mesopotamia [1]
We measure the sensitivity of the root mean squared error (RMSE) metric, calculated using the sampled soil water salinity (ECsw ) at the three depth intervals to ensure that our sensitivity indices are grounded relative to the observed soil salinity
We calibrated and validated a modified zone salinity model developed by Isidoro and Sobol’s methods to first reduce the number of influential model parameters important to and Grattan [17], which was applied to estimate long-term soil salinity in fields irrigated with calibration and that need to be acquired from the field
Summary
Salinization of soils, groundwater, and surface waters from irrigation is a well-known problem often associated with the decline of ancient civilizations dependent on irrigated agriculture around the world, such as Mesopotamia [1]. There is a high economic cost associated with salinity; the US Bureau of Reclamation spends $32 million annually to limit salt additions to the Colorado River and the Natural Resource Natural Resource. Agriculture 2019, 9, 31 water) having greater salinity grows to meet agricultural water demands, a key question inevitably remains, is long-term use of recycled water sustainable? Subsequent irrigation or rainfall can dilute the soil-water salinity or the solutes can be removed from the system by leaching to subsurface drains, or through deep percolation below the root zone. Salinity risks increase when saline water is used for irrigation and when poor fertilizer and poor irrigation management are combined
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