Evaluation of some physiological traits and yield of quinoa (Chenopodium quinoa Wild.) under different irrigation regimes

Water deficit is one of the abiotic stresses that has many adverse effects on crop growth and yield. Understanding the mechanisms of the effect of drought stress on the plant plays an important role in managing different irrigation regimes to deal with adverse environmental conditions and improve crop yield management. Quinoa as a nutritious crop has attracted particular attention in recent years. In arid and semi-arid conditions, quinoa can be successfully cultivated in marginal soils, indicating that quinoa is an unpredictable plant. Today, agriculture needs to increase production per unit area, despite the limited water resources. To achieve the best results from the cultivation of each crop, careful and calculated management is required. Irrigation intervals are one of the most critical strategies that can improve water use efficiency.

An experiment was conducted to investigate the effect of irrigation intervals and amounts on the quinoa's physiological traits and yield at the University of Kurdistan research farm, located in Dehgolan plain. The experiment was arranged in a split-plot scheme based on randomized complete blocks design with three replications. Four irrigation intervals (4, 8, 12, and 16 days) were considered the main factor, and four irrigation levels (100%, 75%, 50%, and 25% of plant water requirement) were considered secondary factors. Giza1 cultivar, which was obtained from the Seed and Plant Improvement Institute, was used for cultivation. Relative water content, membrane stability index, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, carotenoid/total chlorophyll ratio, biological yield, grain yield, and harvest index were measured.

The relative water content of quinoa was decreased when the irrigation intervals increased. The highest decrease (13.87%) was observed in the irrigation interval once every 16 days compared to the control. The highest Relative water content was observed in the control treatment, while there were no significant differences between control and 75% water requirement treatments. The smallest (72.74%) and greatest (81.06%) membrane stability index were observed in 25% crop water requirement and control treatments. The highest chlorophyll a (10.68 mg.g-1 in dry weight), chlorophyll b (3.7 mg.g-1 in dry weight), and total chlorophyll (14.38 mg.g-1 in dry weight) content were observed in 100% crop water requirement with a 4-days interval, which was not significantly different from a 75% crop water requirement treatment with 4-days interval. The smallest (2.82 mg.g-1 in dry weight) and greatest (3.72 mg.g-1 in dry weight) carotenoid content were observed in 25% crop water requirement and control treatments. However, there were no significant differences between control and 75% crop water requirement treatment. Increasing the irrigation interval from 4 to 8 days reduced the biological yield and grain yield by 50.80% and 44.84%, respectively. The highest biological yield (4237 kg.ha-1) and grain yield (1602.6 kg.ha-1) were observed in the control treatment, which was not significantly different with 75% crop water requirement. The lowest (43.94%) and highest (50.78%) harvest index were obtained in the irrigation intervals of 4 and 16 days, respectively. Plants that were irrigated every 4 days at 25% of the plant water requirement had the highest water use efficiency (0.63 kg m-3). Among irrigation amount treatments, the highest harvest index was observed in 25% water requirement. Increasing the irrigation intervals increased the grain protein content so that the 16-days irrigation interval treatment had the highest protein content, although it was not significantly different from the 12-day irrigation interval. The lowest grain protein content was observed in the control treatment, which was not significantly different with a 75% crop water requirement treatment. Drought stress reduced the relative leaf water content, membrane stability index, chlorophyll content, leaf carotenoids, biological yield, harvest index, and quinoa seed yield.

The results of the present study showed that despite the negative effects of drought stress on some physiological parameters, quinoa plant showed good relative resistance against water shortage, so that by providing just 25% of crop water requirements 812 kg.ha-1 could be achieved, which is considerable compared to many crops. Due to the fact that irrigation by 75% of plant water requirement did not reduce grain yield compared to control conditions, so this treatment can be used to irrigate the plant.