The researchers studied how the age of rice seedlings affects their quality and yield when machine-transplanted. They used two types of super hybrid rice and found that younger seedlings had higher plant height and dry weight. However, older seedlings had slower leaf growth and lower root-shoot ratio. Seedlings aged 17 days had the highest grain yield due to more panicles, higher seed setting rate, and heavier grains. Younger seedlings turned green faster after transplanting and had more effective panicles. The best age for seedlings in the Yangtze River region was 15-20 days for better quality and higher yield, especially for machine transplanting.