The article presents the results of a study on the formation of fiber flax productivity depending on the combination of genetic characteristics of modern varieties and agrotechnological cultivation factors. It is substantiated that the realization of the high productivity potential of the crop depends not only on varietal biological traits but also on the optimization of cultivation technology elements, particularly the mineral nutrition system. The aim of the study was to determine the patterns of growth, development, and yield formation of fiber flax, as well as to evaluate the effect of different rates of mineral fertilizers on quantitative and qualitative indicators under the conditions of the Western Forest-Steppe.

The research was conducted in 2023–2025 using field, laboratory, and statistical methods on gray forest surface-gleyed soils. The objects of the study were modern fiber flax varieties: Hetman – a high-yielding mid-season variety (76–84 days) with a plant height of 85–90 cm and a fiber yield potential of up to 2.1 t/ha; Gladiator – a mid-season variety resistant to lodging and capable of producing high straw and high-quality fiber yields; Synilga – an intensive-type variety with a high long-fiber output (up to 1.8 t/ha) and disease resistance; Esman – a mid-season variety characterized by high harvesting adaptability. Fertilizer rates N20P40K60, N30P60K90, N45P90K135 were applied.

It was established that the duration of the growing season varied depending on varietal characteristics and mineral nutrition levels. The study proved that fiber flax productivity largely depends on the interaction between genetic and agrotechnological factors. Higher yields of straw and seeds were obtained under optimal fertilizer application rates, while intensive-type varieties demonstrated the greatest responsiveness to increased mineral nutrition. The Hetman variety showed stable high yields of fiber and seeds, Synilga ensured a high output of long fiber, Gladiator demonstrated lodging resistance and high-quality straw formation, and Esman showed superior technological suitability for harvesting.

The obtained results confirm the feasibility of a differentiated approach to the selection of varieties and fertilization systems as key components in realizing the genetic potential of fiber flax. The practical significance of the study lies in optimizing cultivation technologies to increase yield and improve fiber quality.

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