Yield Components and Population Characteristics of Super-High-Yielding Late Japonica Hybrid Rice in Double-Cropping Rice Area Productivity and Eco-physiological Characteristics of Late Japonica Rice in Double-Cropping Rice System Effects of Nitrogen Application Amount and Planting Density on Angle and Length of Top Three Leaves in Double-Cropping Rice Effects of Paddy Soils from Different Parent Materials on Yield and Nutrient Uptake Characteristics of Double-Cropping Rice Difference in Yield and Population Characteristics of Different Types of Late Rice Cultivars in Double-cropping Rice Area Effects of nitrogen application on yield and C/N of double-cropping rice