The combination of NB and reduced the depth of irrigation water could mitigate the negative effects of salinity and drought stresses and improve water productivity (WP) of quinoa. The experiment was carried out in the greenhouse conditions. A two-year study was carried out in a semi-arid area employing a factorial experimental and in the form of a completely randomized design with three replications. The experimental treatments included three levels of salinity (S1: 1 dS m-1, S2: 4 dS m-1, S3: 7 dS m-1), three levels depth of irrigation water (I1: 60%, I2: 80%, I3: 100% of plant water requirement), and three levels of Nano Biochar (NB) (NB1: 0%, NB2: 2%, NB3: 4%). The parameters of leaf area index (LAI), Weight of 1000 seeds (WOS), spike weight (SW), Seed yield (SY) and WP of each pot were carefully measured. Also, the physiological characteristics of the plant, including seed protein (SP), carbohydrate content (CBH), proline (PR) and chlorophyll a and b (CHLa and CHLb) content were measured. The results showed that salinity and drought stress decreased SY 14.1-37.81%, 11.92%- 28.96, respectively. However, the NB up to 2% alleviated salinity and drought stress and increased yield by 40.75% and 26.55%, 13.88% and 10.89% in SW, WOS and LAI, respectively. The use of 4% NB reduced the amounts of PR and CHB by 50.16% and 22.62%. The amount of SP increased by reducing the depth of irrigation water to 80% of the water requirement of the plant and using 2% of NB and salinity of 4 dS m-1. Decreasing salinity and decreasing the depth of irrigation water increased WP. The I1NB2S1 treatment had the highest WP (12.51 kg m- 3), while the I3NB3S3 treatment had the lowest WP (6.15 kg m-3). The use of the appropriate amount of NB caused the reduction of the negative effects of salinity and drought stress and the improvement of the growth of quinoa compared to the control. Therefore, it is recommended to use for the plant, especially in conditions where the plant is under drought stress, or in greenhouses, in order to reduce the amount of water consumed and improve the growth and yield of the plant. Considering that no significant difference in yield was observed between 2 and 4 dS m-1 salinity treatment and the percentage of SP in 4 dS m-1 salinity was higher than 2 dS m-1, it is possible to use water with 4 dS m-1 salinity for quinoa. Generally, the application of NB could be a suitable solution to reduce the negative effects of drought and salinity stress on quinoa and its sustainable production.
