The researchers studied how applying fertilizer at different times before planting affects the growth and nicotine content of tobacco plants. They found that early application of fertilizer increased the amount of plant material and nicotine in the lower leaves. Nicotine levels changed as the plants grew, decreasing in the stalk before topping and increasing after topping. The source of nicotine from fertilizer decreased as the plants grew, but the timing of fertilizer application did not significantly affect this. Overall, applying fertilizer earlier can help tobacco plants grow better without sacrificing quality.