What is the development of rice field rotation in different periods in China?

In rice field rotation, rice-wheat rotation appeared in China before the 9th century at the latest, and it developed more rapidly in the Song Dynasty. According to records, Song Taizong once popularized wheat planting in Jiangnan, Zhejiang, Jinghu, Lingnan, Fujian and other places, which promoted the development of rice-wheat double cropping system.

During the Southern Song Dynasty, because a large number of northerners moved south, the demand for wheat increased sharply. The government encourages wheat planting with the policy of rent-free rice planting, so rice-wheat rotation is more common.

It developed rapidly in Ming and Qing Dynasties, such as planting beans after rice, harvesting beans for wheat, planting wheat or beans or vegetables after double cropping rice, planting sweet potatoes or radishes after double cropping rice, and planting rice after double cropping potato. Some forms of triple cropping system have been gradually extended from Guangdong, Guangxi and Fujian to the Yangtze River basin.

In the Ming Dynasty's Agricultural Records, it was recorded that rice-cotton rotation system appeared in Shanghai and other places. The experience of interplanting edamame in rice fields is recorded in Qi Min Si Shu, San Ji Nong, Getting Rich Documentary and many local chronicles in Qing Dynasty.