Waterlogging is an increasing constraint to crop productivity under climate change, yet information on quinoa’s sensitivity to excess water remains limited. This study aimed to identify the most vulnerable phenological stage of quinoa to waterlogging stress. A greenhouse experiment was conducted using the variety Tunkahuan, applying waterlogging (12 days) at six growth stages according to the BBCH scale, plus a well-drained control. Growth, chlorophyll content, biomass, yield components, and harvest index were assessed. Waterlogging significantly reduced growth and yield at all stages (p ≤ 0.05). Early vegetative stress reduced canopy cover and chlorophyll, with partial recovery after stress removal, but caused 73% plant mortality at BBCH 25. Reproductive stress, especially at anthesis (BBCH 60–67), was most critical, reducing yield by 71–77% compared to the control due to severe declines in grain number and harvest index. Stress during grain filling caused moderate yield reductions (22–28 g plant⁻¹). We conclude that quinoa is sensitive to waterlogging throughout its development, but anthesis is the most vulnerable stage for irreversible yield loss. These findings highlight the need for breeding programs targeting waterlogging tolerance and improved management practices to minimize flooding risk during flowering.

Quinoa is a highly nutritious Andean crop with considerable yield potential that remains underexploited in southern Ecuador. This study evaluated the effects of planting method (row seeding, hill seeding, and transplanting) and plant density (8–20 plants m⁻²) on quinoa growth and yield under Andean highland conditions. A factorial field experiment was conducted using a randomized complete block design with three replicates. Plant density significantly affected grain yield, increasing from 4.4 to 4.8 t ha⁻¹ at 8 plants m⁻² to a maximum of 6.97 t ha⁻¹ at 20 plants m⁻². This increase was mainly driven by a higher grain number per unit area, while thousand-grain weight remained stable across treatments. In contrast, the planting method and its interaction with plant density had no significant effect on yield or yield components. Grain yield showed a strong positive relationship with above-ground biomass, indicating that biomass accumulation was the main driver of yield variation. These results demonstrate that plant density is the primary agronomic factor controlling quinoa productivity under Andean conditions. Optimizing plant density to 15–20 plants m⁻² is recommended as a simple and cost-effective management strategy to maximize grain yield, regardless of planting method.