Effects of potassium application rate on yield and potassium use efficiency of summer maize under high yield conditions Effect of potassium application on crop yields and potassium use efficiencies in a wheat-cotton double cropping system Effect of Potassium Application Rates on Nitrogen Absorption and Utilization of Different Types of Rice Effects of Potassium Application Rate on Stem Lodging Resistance of Summer Maize under High Yield Conditions Effects of rate and time of potassium application on yield and fiber quality of cotton (Gossyium hirsutum L.) at different fruit positions