The study looked at how different amounts of nitrogen fertilizer affect rice yield and nitrogen use efficiency in high, middle, and low-yield paddy fields. They found that using 180 kg/ha of nitrogen resulted in the highest grain yields in high and middle yield fields, while 240 kg/ha was best for low-yield fields. Increasing nitrogen application can improve nitrogen efficiency, but too much can decrease productivity. The optimal nitrogen application rates are 120-180 kg/ha for high and middle yield fields, and 180-240 kg/ha for low-yield fields.