Effect of planting date and irrigation deficiency on the physiological, biochemical, and yield component of quinoa (Chenopodium quinoa Willd) in Mashhad

The proper planting date is known as one of the most important agronomic programs to achieve the optimal yield in crops through increasing adaption of plants to environmental conditions and improving resource use efficiency. The synchronization of growth stages with climatic parameters in terms of rainfall, temperature, and humidity is considered as the main consequence of proper planting dates. One of the most basic methods for improving water consumption patterns in the agriculture sector is the accurate management of cropping and breeding methods, so the implementation of policies to change the pattern of cultivation based on comparative advantage, efforts to reduce the level of crop cultivation requiring high water consumption and developing drought-resistant plants. In this regard, water scarcity is a well-known factor in reducing quinoa yield under arid and semi-arid areas, which can seriously affect crop profitability. Thus, the present study aimed to evaluate the different planting dates and irrigation rounds on physiological traits and growth yield and component yields of quinoa under Mashhad climate.

The current study was conducted at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, in 2020. The experiment was designed as a split-plot arrangement based on randomized complete block design with three replications: planting date (July 6th, July 23th, and August 6th) as main plots and water deficit regimes (7, 14, and 21-d intervals) as subplots. The experimental data were analyzed using SAS 9.4. The mean values were statistically compared according to the least significant difference (LSD) test at the level of 5%.

According to the results, decreasing water availability significantly caused an increase in chlorophyll a, chlorophyll b, and carotenoid contents. Also, leaf osmotic potential at the planting date of August 6th significantly decreased up to 39%, compared with the planting date of July 6th. It seems that in the case of increasing temperature, with increasing leaf osmotic potential, the plant resistance to environmental conditions would be improved. The content of soluble carbohydrates as well as the activity of ascorbate peroxidase and peroxidase enzymes were significantly affected by the interaction between planting date and irrigation. The highest amount of ascorbate peroxidase enzyme was observed in the 21-d irrigation cycle and planting date of August 6th. Ascorbate activity increased with increasing drought stress. The highest content of soluble carbohydrates was found on the date of planting on July 23th and the 14-d irrigation cycle. In addition, grain yield at the 21-d irrigation cycle decreased by 25% compared to the 7-d irrigation cycle. Moreover, the highest grain yield was obtained from the planting date of august 6th (544 g.m-2). Water shortage during the root development stage is a limiting factor against the optimal yield of quinoa

Based on the results, a planting date on August 6th with a 14-d irrigation cycle can be recommended to achieve the desired yield of quinoa along with reducing water consumption in the Mashhad region.