The study looked at how tobacco plants absorb nitrogen from the soil and fertilizer at different growth stages. They used a special technique to track nitrogen movement in the plants. The results showed that nitrogen levels decreased after planting, with the highest amount in the upper leaves. Suckers affected nitrogen levels in other parts of the plant. Upper leaves absorbed more nitrogen from the soil than from fertilizer, while lower leaves took in more nitrogen from fertilizer. Overall, the soil in Enshi provided most of the nitrogen for the tobacco plants.