Yield, oil content, and fatty acid profile of flax (Linum usitatissimum L.) as affected by phosphorus rate and seeding rate

Flax (Linum usitatissimum L.) is an important cash crop for production of edible oil and biodiesel. Experiments were conducted on soils with medium levels of phosphorus (P) at BaiYin (BY) (in 2014 and 2015) and Ulanqab (Ula) (in 2012, 2014, and 2015) aimed at optimizing rate of P rate and seeding rate (SR) for flax seed yield and oil production. The experiments evaluated all combinations of three P fertilizer rates (0, 35, and 70 kg P₂O₅ ha⁻¹) and three seeding rates (450, 750, 1050 seeds m⁻²) with 3 replicates, a split-plot arrangement in a randomized complete block design. Results showed P rate, SR, and their interaction significantly affected seed yield and oil yield, the P rate × environment (E) interaction was significant for palmitic, stearic, oleic, linoleic, and linolenic acid contents, and E significantly influenced oil content. Increased P rate significantly enhanced seed yield, linolenic acid content, and oil yield at the high SR, but not at the low SR. Additionally, the high SR produced greater seed and oil yields, and linolenic acid content compared to the low SR. Application of 35 kg ha⁻¹ P₂O₅ and 1050 seeds m⁻² resulted in higher oil productivity and linolenic acid content. These results indicate that appropriate P rate and SR can improve oil productivity and alter fatty acid profile of flax, and that the magnitude of these effects depends on the growing E. Maximum predicted oil yield was obtained with 50 kg P₂O₅ ha⁻¹ and 1050 seeds m⁻² based on regression analysis when averaged across the five environments. These findings could have important implications for sustainable intensification of flax production in the presence of variable and changing growing environments.