The researchers studied how different amounts of nitrogen fertilizer and plant spacing affect the growth and yield of rice plants. They found that using 165 kg of nitrogen per hectare along with a plant density of 24-27 hills per 104 square meters increased the grain yield. Increasing plant density also improved nitrogen use efficiency in one year but decreased it in another. The combination of nitrogen and plant density influenced leaf area and radiation absorption, which are important for grain production. Too much radiation can decrease efficiency, affecting the amount of energy the plants can use for growth.