Modelling Quinoa (Chenopodium quinoa Willd.) Seed Yield and Evapotranspiration Under Water, Salt and Combined Water-Salt Stress

We studied the responses of quinoa (Chenopodium quinoa Willd.) to single and combined effects of four different irrigation water salinity (electrical conductivity) levels (S1: 0.25, S2: 5, S3:10 and S4: 20 dSm⁻¹), and four water application rates (W1:120%, W2:100%, W3:70 and W4:50% of depleted water from field capacity). The experiment is a fully randomized factorial design with total of 48 weighted lysimeters. Seed yield was 30% higher when water requirement was fully met (W1 and W2) as compared to treatments with water deficit where water requirement was partially met (W3 and W4). Crop water response coefficients were found sensitive (K_y = 1.55) to drought induced water stress but tolerant to salinity induced water stress (K_y = 0.47). We found that quinoa had a salinity threshold value of ~4 dSm⁻¹ (in soil water extract) with a slope of 3.4% (yield loss per dSm⁻¹ increase in soil extract salinity). These data classify quinoa as a moderately salt tolerant crop. We evaluated the combined effects of salinity and water levels on seed yield. We concluded that if there is more than one stress factor, quinoa responded to the stress factor having the highest impact (either salinity or water stress). Seed yield under combined salt and water stress for all treatments was well predicted from the separate responses to water and salt stress using the dominant stress response model. Our results indicate that over the range of conditions studied, quinoa water productivity was more dependent on applied water rate than on salinity.