So, what are the advantages of these three crops from America? What impact has it had on China's population growth? Listen to botanist Shi Jun's careful analysis for us.
Shi Wenjun
poplar
In A.D. 1368, Zhu Yuanzhang made Nanjing his capital and began the rule of the Ming Dynasty. In the following 500 years, although China experienced war and regime change, it remained a unified country during this period. China's population grew rapidly, especially during the Qianlong period of the Qing Dynasty, from 654.38+0.43 billion people in the six years of Qianlong to more than 200 million people now, which is only a few decades.
The Ming and Qing Dynasties were a very frequent and serious period of natural disasters in the history of China, which was obviously not a good thing for ancient agriculture, which almost depended on the weather. So what is the reason for the rapid population growth in this period?
Many historians believe that the introduction and extensive cultivation of various crops in the New World in the late Ming and early Qing Dynasties was one of the important promoters. To understand this problem, we also need to know the introduction time of potatoes, sweet potatoes and corn and their special abilities.
Corn, a kind of defective super grain
There is no doubt that corn, as a food that nourishes American civilization, has an irreplaceable position in the grain circle. Compared with wheat and rice, corn has stronger environmental adaptability and good yield. Corn is suitable for planting in arid mountainous areas. Besides the developed root system, it is more important to have a special photosynthesis pathway-C4 pathway.
Generally speaking, when plants carry out photosynthesis, they use carbon dioxide that enters the stomata of leaves. However, the concentration of carbon dioxide in the air is limited, which greatly limits the efficiency of photosynthesis. C4 plants, such as corn, have a brilliant idea, which is to concentrate carbon dioxide first and then carry out photosynthesis. Carbon dioxide entering maize mesophyll cells will combine with phosphoenolpyruvate (PEP) to produce oxaloacetic acid with four carbon atoms (hence the name C4 pathway), which will be converted into malic acid or aspartic acid. Subsequently, these special acids will be concentrated and sent to the leaf sheath, where they will be decomposed into carbon dioxide and pyruvate again. In this way, the concentration of carbon dioxide in leaf sheath cells increases, and the photosynthetic efficiency naturally increases.
In addition, C4 plants also have amazing water use efficiency. C4 plant only needs 230 to 250 ml of water to produce 1 g dry matter, while C3 plant consumes two to three times as much water. Because of this, corn has become an important food crop in arid areas at middle and high altitudes.
In addition to good varieties, corn is also rich in a large number of nutrients needed by the human body. Carbohydrate in fresh corn accounts for 74% of dry matter, and protein accounts for 9.4%. Because of its rich nutrition, corn was used as a staple food by Mayans in America as early as 8000 years ago.
But compared with rice and wheat, corn has an inherent disadvantage-if it is not treated with alkaline solution, the nicotinic acid contained in corn seeds cannot be released. Due to the lack of nicotinic acid, a special vitamin, people who eat corn will suffer from pellagra. Fortunately, China people's recipes are rich in food, which naturally solves this problem.
Sweet potato, the strong point of natural transgenic crops
Although in South America, the status of sweet potato has never been as high as that of corn, sweet potato is also a food crop with its own aura. Sweet potato is a natural transgenic crop, and this transgenic time occurred about 1 10,000 years ago. Yes, we humans didn't do it. It was arranged by nature.
In fact, the roots of sweet potato ancestors are not strong, more like Adenophora adenophora and Platycodon grandiflorum that we see today. However, just 6.5438 million years ago, a sweet potato was invaded by a bacterium called Agrobacterium tumefaciens, survived tenaciously, and obtained a special gene, which made the offspring embark on the road of "getting fat".
Agrobacterium tumefaciens is the most commonly used tool for scientists in today's laboratory. This kind of bacteria has a special DNA—— called plasmid, which can "carry" some genes on themselves like "porters" and send them to the genome of infected organisms. 654.38+0 million years ago, the plasmid of Agrobacterium tumefaciens inserted gibberellin gene into the genome of sweet potato, thus achieving today's sweet potato.
Fat sweet potato has amazing energy supply ability and is a pure carbohydrate provider. 100g raw sweet potato contains 24.7g carbohydrates. In addition, orange potato varieties contain a lot of β-carotene, which is very beneficial for people who lack vitamin A to supplement nutrition. It is worth noting that during the cooking process, some components in sweet potato will change, especially vitamin C will be lost due to long-term cooking and baking. Therefore, a balanced and diverse diet is the real solution.
Just delicious sweet potatoes can also bring some trouble. For example, eating too many sweet potatoes is easy to burn. This "heartburn" is actually a manifestation of hyperacidity. Starch and dietary fiber in sweet potatoes can stimulate gastric acid secretion in large quantities, so there are symptoms of heartburn.
However, despite its shortcomings, sweet potato has gradually become an important supplementary food after entering China. Farmers in China have also creatively improved the planting techniques of sweet potato cutting propagation. Like most convolvulaceae plants, sweet potato also has strong vegetative reproduction ability. Their vines can be extended continuously, and they can take root and sprout in suitable places and grow new roots. Clever farmers in China took advantage of this characteristic of sweet potato, and greatly improved the efficiency of sweet potato planting by cutting vines for reproduction.
During the Wanli period of the Ming Dynasty, Fujian Governor Jin recorded the methods of natural seedling raising on land and overwintering old vines in the Biography of Seven New Overseas Stories: "If vines are used as seedlings, they must be planted vertically and densely, such as raising onions and leeks." With the popularization of these technologies, sweet potato has become an important food crop in China.
Potatoes, the perfect food from heaven.
If corn and sweet potato have some nutritional defects more or less, then potatoes are simply delicious on the table. There is no shortage of starch, protein and vitamins in potato chips, which can not only fill people's stomachs, but also keep people healthy, because vitamin C, B vitamins and minerals are sufficient, and even dietary fiber, which is highly praised by the nutrition community at present, has not fallen behind.
Potatoes can completely meet the nutritional needs of the human body as long as vitamin A and calcium are supplemented. This is not a problem at all for China people who have Chinese cabbage and spinach. How popular potatoes are can be seen from its many nicknames: potato, potato, ground egg and yam egg.
In South America, the origin of potatoes, people have been planting potatoes for more than 7,000 years. The cultivated potato is not a species, but a plant belonging to Solanaceae, including six cultivated species such as Solanum tuberosum, the most common potato.
Potato has become the most adaptable food crop because of its super-high species diversity and genetic diversity. In the alpine mountainous area where corn and sweet potato can't get involved, it bears the heavy responsibility of supplying food. Generally speaking, it takes 250 to 300 cubic meters of water to grow one acre of wheat, which is enough for potatoes to grow on two acres of land; It is a very serious matter that the average yield of grain crops per mu reaches 1000 kg, and the yield of potatoes per mu can easily climb to 3000 kg. Therefore, it is reasonable for potato to become the core grain variety in many areas.
When did the three major American crops enter China?
Therefore, corn, sweet potatoes and potatoes are really excellent food crops. When were these crops introduced into China from the United States and directly affected the population growth?
When and by what means was corn introduced into China? There are still different answers to this question, but many scholars believe that there are three routes: southwest land, northwest land and southeast sea. Among them, the "Longchuan County Records" in the seventh year of Wanli in the Ming Dynasty recorded "Pearl" side by side with millet and rice, which was the earliest corn. In the thirty-ninth year of Jiajing in Ming Dynasty, Pingliang Fuzhi recorded that "wheat is like wheat", which is the earliest record of planting corn in China history. In the forty-two years of Jiajing in Ming Dynasty, Dali recorded "Yumai", namely corn. These records show that there is a parallel relationship between the spread of maize in different ways in time.
At the beginning of its introduction into China, corn was not the main crop. Professor Han of Peking University expounded a viewpoint in the book Historical Agricultural Geography of China that corn was still a rare food in Wanli period, because Jin Ping Mei written in this era recorded that there were tortillas in Ximen Qing's meals. It just shows that in this period, corn is scarce and can only appear on the table of dignitaries. The large-scale popularization of corn was in the dry period. The planting area of corn first extended to the lower reaches of the Yellow River and gradually extended to the north of the Great Wall, becoming an important food crop.
There are many controversies about the introduction of potatoes, but it is certain that potatoes were introduced into China several times through various routes. /kloc-potatoes introduced to the southeast coast in the 0/7th century adapted to high altitude areas, and soon disappeared in subtropical areas, leaving only some residues in some mountainous areas in the southwest and northwest. Later18th century, western missionaries or businessmen brought ordinary potatoes, and they really started their expansion journey.
The path of sweet potato introduction is clear. It was first introduced to Fujian (Fuzhou Changle) from the Philippines by Fujian businessman Chen Zhenlong. According to "New Overseas Biography VII", "Sweet potatoes spread overseas because of their names", this is the earliest record of sweet potatoes in ancient China. Sweet potato has been introduced to Quanzhou, Fuzhou, Zhangzhou and other places from the Philippines many times. Among them, the introduction of Fuzhou was the most influential, and the introduced seedlings were later extended to Zhejiang, Shandong, Henan and Hebei. According to the article "Introduction Experiment of Sweet Potato" published by Liang Jiamian and Qi in Journal of South China Agricultural University 1980, several incidents of introducing sweet potato from Vietnam to Guangdong were clearly recorded.
In addition to the above two main ways, there are some documents showing that sweet potato entered Taiwan Province Province through Brunei and was introduced into Yunnan by land from India and Myanmar.
In this way, the expansion and development of exotic crops takes time, and how much they contribute to the explosive population growth needs to be discussed.
Agricultural production technology has increased grain output.
In fact, during the Ming and Qing Dynasties, the cultivation techniques of traditional food crops such as rice and wheat also made great progress. First of all, it is manifested in the promotion of three crops in two years in the north, two crops in the south and three crops in one year. Through the improvement of rice varieties and the popularization of rice-wheat continuous cropping technology, the land use efficiency has been greatly improved. Incidentally, after corn entered China, in some arid areas, a continuous cropping mode with corn as the core gradually formed, which is self-evident.
At the same time, the technology of improving farmland fertility has been developed by leaps and bounds. Sesame cakes and bean cakes left over from oil pressing can not only be applied to the fields, but also be widely planted with green manure such as alfalfa and Chinese milk vetch to improve soil fertility.
It must be said that the use of green manure is a milestone in the development of ancient agriculture in China and can be called the originator of organic agriculture. But in general, green manure can only alleviate the problem of insufficient soil fertility to a certain extent. If we want to continue to increase production, we need to add a lot of other fertilizers, such as phosphate fertilizer.
Farmers in China have been using animal bones to make soup to fertilize for a long time, and in the Ming and Qing Dynasties, this practice was upgraded to smelting ashes. Bao Yang, an agronomist in the Qing Dynasty, mentioned in the Outline of Knowing Books: "All animal bones, hoof horns and clams are burnt yellow, ground and sieved, and manure is used to cool rice seedlings and irrigate vegetable fields, which is more fertilizer than other manure." This practice greatly improves the effectiveness of fertilizer. In the Ming and Qing Dynasties, the related works "Tiangong Wu Kai Yi Dao" and "Xu Guangqi's Handwriting" all mentioned the situation of fertilizing fields with animal ashes.
The application of new crop varieties and new farming techniques will greatly improve the land use efficiency and total grain output, but we should also pay attention to the lag of crop dissemination and technology popularization. In addition, some special historical events may also have a decisive impact on demography. After Yongzheng carried out the New Deal, the feudal economic form in rural areas of China developed to the extreme. This is a major reform of China's tax system in the late feudal period, which changed the dual tax system combining taxation with talents into a single land tax system. After the land is spread evenly to mu, landless farmers will no longer pay Ding Yin, and the burden on farmers with less land will be much less, which greatly promotes the development of agriculture.
At the same time, the introduction and large-scale planting of new crops such as corn, potato and sweet potato have greatly improved the land production efficiency in alpine and cold areas, the grain planting area has expanded rapidly and the living conditions of farmers have been greatly improved.
Undoubtedly, the introduction of exotic crops directly affects the distribution pattern of population in China, especially the expansion of cultivated land utilization and cash crop planting area in the middle and lower reaches of the Yangtze River, which in turn affects the industrial layout in this area. In the middle and lower reaches of the Yangtze River, where cotton textile industry thrives, the bud of capitalist production relations has emerged, which is closely related to grain production. However, with the invasion of imperialism, China gradually became a semi-feudal and semi-colonial society. What changes have taken place on the dining table of China people during this period? Listen to the next decomposition.
Proofreading | Yujin