In order to estimate kochia (Kochia scoparia) water use efficiency (WUE), an experiment was performed in Birjand, a dry and saline area in South Khorasan, Iran, by using irrigation water of three different salinity levels, i.e. 1.5, 8.6, and 28.2 dSm-1. Several measurements were conducted during the growth season to determine radiation fraction passed through canopy and leaf area index, thereby ground cover percentage was calculated. Reference crop evapotranspiration calculated using Hargreave’s method, corrected by FAO, and after drawing crop coefficient curves, crop evapotranspiration was determined. Ultimately, crop WUE in different salinity levels was calculated for forage and seed yields. Evaluation of crop coefficient curves showed that salinity caused a delay in initial season growth and forced plant maturity in late season. The mean crop evapotranspiration between salinity treatments was equal to 915 mm. WUE was affected by salinity, more than by evapotranspiration, showing biomass production is more sensitive to salinity than crop evapotranspiration. For forage yield, salinity enhancement from 1.5 to 8.6 dSm-1 caused WUE to be increased slightly from 11.5 to 11.9 kg ha-1 per each mm evapotranspiration, though at higher levels of salinity it decreased to 7.6 kg ha-1 per each mm evapotranspiration. WUE for seed yield in 1.5, 8.6, and 28.2 dSm-1 were 2.92, 2.42, and 2.44 kg ha-1 per each mm evapotranspiration, respectively. As forage use is the main purpose of kochia production, it seems that its biomass production have a high tolerance to water and soil salinity.

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