The study looked at how different levels of nitrogen affect the roots and nitrogen use of oil flax plants. They tested four nitrogen levels on oil flax plants in soil columns. The results showed that nitrogen can slow down root growth at first, but then increase root length, diameter, and surface area. The best nitrogen level for oil flax plants was medium nitrogen, which led to the highest grain yield. Shallow roots grew more with high nitrogen levels. Overall, a nitrogen rate of 105kg·hm-2 was recommended for the best balance of plant growth and nitrogen use efficiency.