The researchers studied how different types of rice plants respond to varying levels of nitrogen fertilizer. They tested nine popular rice varieties at five different nitrogen levels. They found that increasing nitrogen levels led to higher grain yields in all rice varieties. Some varieties, like No. 3 and No. 4, showed the best balance of high yield and efficient use of nitrogen. No. 3 had the highest nitrogen recovery efficiency, while No. 4 had the highest agronomic efficiency. These findings suggest that certain rice varieties can produce more grain while using nitrogen fertilizer more effectively.