Botanical history of rice

The development of rice is inseparable from the economic development in the south. As mentioned earlier, the ancient economic and cultural center of China was in the Yellow River Basin, and the south was relatively backward. Gong Yu ranked the land in the south last. Biography of Historical Records of Huo Zhi said: The humidity in the south of the Yangtze River is low, and people's life span is not long. The Biography of the Thirteen Kings in the History of Han Dynasty says: Changsha is a poor place with low humidity. Judging from the population statistics in the second year of Emperor Ping of Han Dynasty (AD 2), the Great Plains of North China and Guanzhong were the most densely populated places at that time, while the population in Jiangnan was very sparse. For example, Yuzhou (now a part of Henan Province) only accounts for about 2% of the country's total area, but its population is more than 7.55 million, accounting for more than 13% of the country's total population. A * * has established 108 counties; Zhang Yu county (now Jiangxi province) is twice as big as Yuzhou, but it has only 350,000 people, 18 counties. This clearly reflected the economic situation south of the Yangtze River at that time, which was far less than that of the Yellow River Basin. At that time, the population of each region was closely related to the local grain output. So although rice is the main crop in the south, the total output is far less than that of millet, the main crop in the north. During the Eastern Han Dynasty, the population in the south gradually increased. At the end of the Eastern Han Dynasty, due to years of war, the social economy of the Yellow River basin suffered great damage, and a large number of people from the Central Plains fled into the Yangtze River basin. After the demise of the Western Jin Dynasty, the situation in the north was chaotic for a long time, and later more people from the Central Plains moved south. These immigrants from the south not only increase the manpower in the south, but also bring high production technology to the north, which is very favorable for the economic and cultural development in the middle and lower reaches of the Yangtze River. But there are many differences between the natural environment in the south and the corresponding crop cultivation methods in the north. Rice requires high growth conditions and cultivation techniques. First of all, rice needs the right amount of water on the field. Although there is a lot of rainfall in the south, we should pay attention to water conservancy irrigation. Because the south is hilly, the hillside can't store water; There are also many low-lying areas that are easily flooded, which brings certain difficulties to the land use in the south. Therefore, although the economy and culture of the Yellow River Basin were equally developed in the long period from the Spring and Autumn Period to the Warring States Period to the Qin and Han Dynasties, the southern region was still sparsely populated, and its economic and cultural development was not as good as that of the Central Plains.