Аннотация
Flax ( Linum usitatissimum L.) productivity in sharply continental climates is highly sensitive to varietal genetics and agronomic management, yet optimal seeding strategies and their genotype-specific responses remain poorly quantified. This two-year field study (2024-2025) in northern Kazakhstan evaluated the interactive effects of variety and seeding density on yield architecture, productivity stability, and fiber quality across five oil and long-stem flax cultivars (Grant, Lada, Taler, Kostanay Yantar (Kost_yantar), UF1 (Chinese-selected-long-fiber-cultivar)) sown at 10 and 23 million seeds ha −1 . Seeding rate exerted a strongly genotype-dependent effect: while Grant and Lada showed minimal response, Kost_yantar, Taler, and UF1 significantly increased capsule number at higher seeding rates. Maximum productivity consistently occurred in plants reaching 80-90 cm in height. Yield analysis identified Taler as the highest-yielding cultivar (∼6.0 t ha −1 ), albeit with pronounced interannual variability, whereas Kost_yantar and Grant demonstrated superior yield stability. Correlation modeling revealed that higher seeding densities generally reduced individual plant productivity, capsule count, and 1000-seed weight. At the same time, yield was most strongly driven by 1000-seed weight (r = 0.58) and seed number per plant (r = 0.45). Fiber quality profiling further distinguished UF1 as the optimal genotype for premium textiles due to superior length, tensile strength, flexibility, and color grade, whereas Kost_yantar was best suited for industrial or low-grade applications. These findings highlight the necessity of precision sowing strategies tailored to varietal genetics and end-use objectives. By matching cultivars to targeted plant densities, prioritizing stable yield architectures, and selecting for high seed mass, producers can substantially enhance flax productivity and fiber-quality under continental agroclimatic constraints.