What is the reason why Ningxia Plain became the frontier of the south of the Yangtze River?

The reason why Ningxia plain became the frontier of Jiangnan;

Yinchuan plain is flat; The Yellow River flows through it, which is conducive to the excavation of canals to divert irrigation from the Yellow River. River alluvial makes the surface form fertile soil; Conducive to farming. On the Ningxia Plain, the Yellow River criss-crosses, and there are many water diversion channels, so large areas of farmland can be irrigated. Coupled with good lighting conditions, rice, wheat, corn, flax and other crops are very suitable for growing here, so it is known as Jiangnan.

It borders on the south of the Yangtze River, formerly known as "South of the Jiangbei River", and first refers to the Hedong Irrigation Area of the Yellow River in northern Ningxia today, which is also the Yellow River Irrigation Area in Ningxia today. Today refers to the Yellow River Plain in Ningxia, including Yinchuan, Wuzhong, Shizuishan and Zhongwei in northern Ningxia. Since ancient times, the Qin and Han canals have been built and irrigated by the Yellow River. Agriculture and animal husbandry are developed, with many lakes, contiguous wetlands and beautiful scenery, which is better than Jiangnan. There are national 5A-level scenic spots such as Hu Sha and Shapotou, which are represented by natural scenery, Shuidonggou, Xixia Mausoleum and Zhenbeibao Film and Television City, which are represented by history and culture, as well as Helan Mountain, China Returned Cultural Park, Cuiming Lake, Yellow Crane Tower, Yellow River Altar and many other scenic spots.