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Drought and salinity are the two major factors limiting crop growth and production in arid and semi‐arid regions. The separate and combined effects of salinity and progressive drought in quinoa (Chenopodium quinoa Willd.) were studied in a greenhouse experiment. Stomatal conductance (gs), leaf water potential (Ψl), shoot and root abscisic acid concentration ([ABA]) and transpiration rate were measured in full irrigation (FI; around 95 % of water holding capacity (WHC)) and progressive drought (PD) treatments using the irrigation water with five salinity levels (0, 10, 20, 30 and 40 dS m−1); the treatments are referred to as FI0, FI10, FI20, FI30, FI40; PD0, PD10, PD20, PD30, PD40, respectively. The measurements were carried out over 9 days of continuous drought. The results showed that increasing salinity levels decreased the total soil water potential (ΨT) and consequently decreased gs and Ψl values in both FI and PD. During the drought period, the xylem [ABA] extracted from the shoots increased faster than that extracted from the roots. A reduction in ΨT, caused by salinity and soil drying, reduced transpiration and increased apparent root resistance (R) to water uptake, especially in PD0 and PD40 during the last days of the drought period. The reasons for the increase in apparent root resistance are discussed. At the end of the drought period, the minimum value of relative available soil water (RAW) was reached in PD0. Under non‐saline conditions, Ψl decreased sharply when RAW reached 0.42 or lower, but under the saline conditions of PD10 and PD20, the threshold values of RAW were 0.67 and 0.96, respectively. In conclusion, due to the additive effect of osmotic and matric potential during soil drying on soil water availability, quinoa should be re‐irrigated at higher RAW in salt‐affected soils, i.e. before the soil water content reaches the critical threshold level causing the drop in Ψl resulting in stomatal closure.

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Drought and salinity reduce crop productivity especially in arid and semi‐arid regions, and finding a crop which produces yield under these adverse conditions is therefore very important. Quinoa (Chenopodium quinoa Willd.) is such a crop. Hence, a study was conducted in field lysimeters to investigate the effect of salinity and soil–drying on radiation use efficiency, yield and water productivity of quinoa. Quinoa was exposed to five salinity levels (0, 10, 20, 30 and 40 dS m−1) of irrigation water from flower initiation onwards. During the seed‐filling phase the five salinity levels were divided between two levels of irrigation, either full irrigation (FI; 95 % of field capacity) or non‐irrigated progressive drought (PD). The intercepted photosynthetically active radiation was hardly affected by salinity (8 % decrease at 40 dS m−1) and did not differ significantly between FI and PD. Radiation use efficiency of dry matter was similar between salinity levels and between FI and PD. In line with this, no negative effect of severe salinity and soil–drying on total dry matter could be detected. Salinity levels between 20 and 40 dS m−1 significantly reduced the seed yield by ca. 33 % compared with 0 dS m−1 treatment owing to a 15–30 % reduction in seed number per m2, whereas the seed yield of PD was 8 % less than FI. Consequently, nitrogen harvested in seed was decreased by salinity although the total N‐uptake was increased. Both salinity and drought increased the water productivity of dry matter. Increasing salinity from 20 to 40 dS m−1 did not further decrease the seed number per m2 and seed yield, which shows that quinoa (cv. Titicaca) acclimated to saline conditions when exposed to salinity levels between 20 and 40 dS m−1.