Tillering Characteristics and Its Relationship with Population Productivity of Super-High Yield Rice Population of Yongyou 12 Accumulation, Distribution, and Utilization Characteristics of Phosphorus in Yongyou 12 Yielding over 13.5 t ha-1#br# Plant-type Characteristics in Populations with Different Yield of Yongyou 12 Population Characteristics for Super-High Yielding Hybrid Rice Yongyou 12 (>13.5 t ha-1) Potassium Nutrition Characteristics in Different Yield Populations of Super Rice Yongyou 12