Effect of drought stress and nitrogen chemical fertilizer on root properties and yield in three quinoa cultivars (Chenopodium quinoa Willd)

The world population is increasing daily, while the scope for expansion and development of agricultural land is very narrow due to limited water resources. All of this can affect agriculture indirectly or directly. Quinoa is a pseudo-cereal, belongs to the Amaranthaceae family, and is native to South America. This crop is important for human and animal nutrition due to its medicinal and agro-industrial properties. Water and nitrogen (N) are two major challenges in quinoa cultivation that can be addressed by better understanding related agronomic features. Under water deficit conditions, selecting and cultivating crop species tolerant to drought stress is an approach to maintaining and/or increasing crop production levels. Although it is widely reported that quinoa is a highly drought-tolerant crop, its growth has been significantly suppressed under severe drought stress conditions. The experiment was conducted as a split factorial arranged in a randomized complete block design with three replications. Treatments included four irrigation regimes (100, 80, 60, and 40% of crop water requirement) as the main factor, three quinoa cultivars (TITICACA, Q29, and GIZA1), and three nitrogen fertilizer rates (0, 100, and 200 kg ha1 from urea sources) as subfactorial. The field preparation operations prior to planting included plowing and disc Planting was done on March 22, 2021. The net amount of nitrogen-based nitrogen fertilizer treatments of 100 and 200 kg ha-1 was equal to 46 and 92 kg, respectively. According to the soil test results, the soil was not poor regarding phosphorus and potassium elements, so only urea fertilizer was used. The distance between two rows and between plants on the row in quinoa cultivation was 50 cm and 10 cm, respectively. There was a significant interaction effect between irrigation, N, and cultivar on root traits and grain yield. The effects of irrigation regimes, N rates, and their interactions were significant on plant height at the level of one percent, and the highest (109 cm) and lowest (50 cm) plant heights were obtained with normal irrigation and 100% N application in the GIZA1 cultivar and 40% of the water requirement of 100 kg ha-1 N application in cultivar Q29, respectively. The highest 1000-seed weight was obtained with the normal irrigation (2.93 g) regime to meet 80% of the water requirement (2.91 g) in the GIZA1 cultivar. The lowest 1000-seed weight was obtained with 40% of the plant water requirement in all three cultivars. Thousand-grain weight in Q29 and TITICACA cultivars is the same in all irrigation regimes. Two treatments of the normal irrigation, N application and GIZA1 cultivar; and 40% of water requirement, 200 to 100 kg ha-1 of N rate and Q29 cultivar obtained the highest (3326 kg ha-1) and lowest (686 kg ha-1) seed yield, respectively. The N addition reduced seed yield in quinoa cultivars under water -deficit conditions. In water deficit conditions, the application of nitrogen fertilizer decreased the biological yield of quinoa cultivars, and increasing the irrigation water and using urea fertilizer significantly increased the biological yield of quinoa. Also, in 60, 80, and 100 % of water requirement treatments, the amount of biological yield in the cultivar GIZA1 was higher than the other two cultivars. This research showed that the quinoa plant has a high drought tolerance. In such a way, it could complete its growth period and have acceptable performance in conditions of intense stress. With the higher N application, the GIAZ1 cultivar performed better than the others. Although the TITICACA cultivar recorded a lower grain yield under optimum irrigation conditions, it showed a higher grain yield under severe stress conditions than others. It can be concluded that under the conditions of 100% water requirement and the application of 200 N kg ha-1, GIAZ1 variety is suitable for the growth of quinoa in the ecological conditions of the Ilam region.