Scheduling Quinoa Irrigation by Crop Water Stress Index

This study aimed to calculate the crop water stress index (CWSI) of Quinoa. This study was conducted in a completely randomized design with four irrigation levels of 100 (T1), 75 (T2), 50 (T3), and 25 (T4) % of crop water requirements in three replications, and experimental treatments and measurements were mainly carried out during Quinoa growing season at 2017-2018 years. The results revealed that the highest of leaf, stem, root, inflorescence dry weights, and biomass by 11.3, 8.8, 2.8, 16.8, and 39.7 g were in the T1 treatment. Using the T2, T3, T4 compared with T1 were decreased grain yield (by 37.6, 52.5, and 64.8%), harvest index (by 30.4, 34.5, and 30.7%), Biomass (by 16.4, 29.7, and 51.1%). But, using these treatments was increased WUE (by 19.4, 36.6, and 77.4%) compared with T1. CWSI correlated significantly (P < 0.01) and negatively with grain yield and biomass. The results revealed that increased CWSI values with reduction of quinoa grain yield. Also, the results showed that the highest and lowest quinoa grain yield at average CWSI values of almost 0.05 and 0.61. Therefore, to achieve the highest grain yield in irrigation, the quinoa crop should be irrigated at 0.05 of the CWSI. The lowest CWSI values were observed in T1(by 0.04) and the highest in T4 (by 0.72). In this study, the average CWSI was calculated in the days before irrigation in T1, T2, T3, and T4 treatments, and its values were 0.05, 0.19, 0.48, and 0.72, respectively. The results also revealed that with crop water requirement change from 100 to 75 percent, the CWSI was about 3.8 times higher. Accordingly, the CWSI can be used to plan irrigation. The best irrigation time is based on T1 treatment when (Tc-Ta)a=2.41-0.21 VPD (5≤VPD≤20).