The researchers studied how different levels of nitrogen affected the growth and yield of BARI Tomato-9. They tested four nitrogen levels: no nitrogen, 100 kg/ha, 150 kg/ha, and 200 kg/ha. The plants with 150 kg/ha of nitrogen grew the tallest, had the most leaves, branches, flowers, fruits, and clusters, and produced the largest fruits with the highest yield. Overall, the plants responded positively to higher nitrogen levels, with 150 kg/ha being the most effective for the growth and yield of BARI Tomato-9.