| Summary: | The overall aim of this research was to optimize nitrogen (N) fertilization of plants under desalinated water and a wide range of chloride concentrations for high yield while minimizing downward leaching of nitrate and chloride. The response of two crops, lettuce and potato, to N concentration (C<sub>N</sub>) in the irrigating solution using desalinated and wide range of Cl concentrations (C<sub>CL</sub>) was evaluated. The yields of both crops increased with N up to optimal C<sub>N</sub> of the irrigating solution and decreased as C<sub>CL</sub> increased. Optimal C<sub>N</sub> in both crops was higher in the desalinated water than high C<sub>CL</sub> treatments. N uptake by plants increased with C<sub>N</sub> in the irrigating solution and the highest uptake was at low C<sub>CL</sub>. As expected, N fertilization suppressed Cl accumulation in plant tissues. Drainage of N and Cl increased with increase in C<sub>CL</sub> in the irrigating solution and N fertilization above optimal C<sub>N</sub> resulted in steep rise in downward N leaching. The overall conclusion is that as water quality is improved through desalination, higher N supply is required for high yields with less groundwater pollution by downward leaching of N and Cl.
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