The researchers studied how the quality of leaves in rice plants affects grain yield. They used different planting densities and nitrogen fertilizer levels on two types of rice plants. They found that for rice plants with high grain yield, having the right amount of leaf area at the heading stage is important. During the filling period, a high photosynthetic potential and photosynthetic potential per grain ratio are key for a good harvest. By applying fertilizer to the panicles based on leaf area at the heading stage, they were able to maintain leaf area, increase photosynthetic potential, and ultimately achieve higher grain yield.