The researchers studied how different types of nitrogen affect the growth and quality of tobacco plants. They found that a balanced ratio of ammonium to nitrate nitrogen (50:50) led to the best results, with faster growth, improved photosynthesis, and higher levels of important chemicals in the leaves. This balanced ratio also increased tobacco yield and quality, resulting in better economic profits. Overall, using a 50:50 ratio of ammonium to nitrate nitrogen is the most effective way to improve tobacco growth and quality at the same time.