When (which dynasty) did terraces begin to exist in ancient China?

At least since the Qin and Han Dynasties, China has had terraced fields. The cultivation of rice requires a large area of ponds, but there are many hills in the southeastern provinces of China, and there are few plains suitable for rice cultivation. In order to solve the food problem, farmers who immigrated here built terraces and used dams to store water, which made it possible to grow rice in a large area in hilly areas and solved the local food problem. However, planting terraced fields consumes much more manpower than the plain, and there is no advantage in yield. Moreover, the vegetation in hilly areas is seriously damaged, so this farming method is gradually eliminated and only continues to exist as a tourist resource. Terraces in China are mainly distributed in mountainous areas in the south of the Yangtze River, mostly in Guangxi and Yunnan. This is because these places are rainy and mountainous, and terraced fields are built by mountains, among which Ailao Mountain in Yunnan and Longji Terraced Fields in Longsheng, Guangxi are more famous.