Ancient China was built on a riverside so it was easy to grow crops. Due to lack of animal manure sometimes they had to use human waste to fertalise the crops. They fertalised their fields so that they could use it for many many years in the future. This type of producing crops grew popular all over China this increased the population aswell. Eventually the population grew to 100 million people. The reason we know all we do about the farming of ancient China is because the Chinese wrote a book called "The Book of Odes"