Photosyntheticcharacterization and yield of summer corn (Zea mays L.) during grain filling stage under different planting pattern and population densities Dry Matter Production and Photosynthesis Characteristics of Three Hybrids of Maize (Zea mays L.) with Super-High-Yielding Potential Effects of nitrogen application stages on photosynthetic characteristics of summer maize in high yield conditions Effects of nitrogen application dates on yield and nitrogen use efficiency of summer maize in super-high yield conditions Carbon and Nitrogen Metabolism and Nitrogen Use Efficiency in Summer Maize under Different Planting Densities Responses of Photosynthesis Characteristics to Nitrogen Application Rates in Summer Maize (Zea mays L.)