Improvements in farming machinery included, for example, the moldboard plow and watermill. Later, cotton planting and weaving technology were adopted and improved.
While around 750, 75% of China's population lived north of the river Yangtze, by 1250, 75% of population lived south the river. This migration was possible due to the introduction of quick-ripening strains of rice from Vietnam suitable for multi-cropping.
I did some research and the lowest range was 1,000,000 and the highest was 1,700,000. Its hard to estimate this because they didnt have the proper recording instruments we have today.
