Most Chinese regard the Tang dynasty as the highpoint of imperial China, both politically and culturally. The empire reached its greatest size prior to the Manchu Qing dynasty, becoming the center of an East Asian world linked by religion, script, and many economic and political institutions. Moreover, Tang writers produced the finest poetry in China’s great lyric tradition, which has remained the most prestigious literary genre throughout Chinese history. But like most other dynasties that endured for centuries, this was also an age of transformation. The world at the end of the Tang was quite different from what it had been at the beginning, and the dynasty’s historical importance is a consequence of the changes that took place during that time.
By the late Tang, farmers in southern China prepared rice grains by steeping them in a solution made from boiled animal bones, sometimes mixed with silkworm droppings or sheep dung, and then sowed the grains in special seedbeds that had been prepared by repeated deep plowing to break up the soil.
Next, the beds were covered with wood ash and turned over several times with the plow at the beginning of spring before being fertilized with animal or human manure and rotted hemp stalks. By preparing fields in this way for the same staple crops year after year, Chinese farmers actually improved the fertility of their soil over time, while decreasing the threat of insects and disease.
In addition to using new methods of seed preparation, Tang farmers used new materials as fertilizers. During the late Tang and into the Northern Song, organic animal manure became the primary fertilizer in the south, and farmers began to build brick-lined manure houses near their dwellings for storing this precious commodity. The availability of animal fertilizer was closely linked to the increased use of draft animals in plowing. The farmer Lu Guimeng, in a blessing for an ox pen, described how large numbers of oxen were raised together in pens, from which fertilizer could be extracted easily. At a rate of twenty-five cubic yards of manure per ox per year, Lu Guimeng, who owned about a dozen oxen, could have met most of his need for fertilizer from his own animals. Farmers who exceeded their own needs sold the excess as a commercial product.
The sale of human manure (nightsoil) became an important business in this period, as entrepreneurs began to specialize in collecting human excrement in cities for sale in the countryside. While the use of nightsoil as fertilizer may have dated from ancient times (a question that is difficult to resolve because the terminology does not distinguish human waste from animal), the first clear records of this practice date from the late Tang. Nutrient-rich mud scooped from the bottoms of rivers—which were numerous in the south—became another important fertilizer during the Tang, as did lime in certain areas. Farmers of the Northern and Southern Dynasties had introduced green manures—fertilizers made from plants grown solely for the purpose of being plowed back into the soil to improve its fertility and make it easier to work—most notably nitrogen fixing beans. This practice continued into the Tang, with an increase in the variety of plants that were used.
The reasons had to do with the limited space that had been opened, the technological conservatism or parsimony of the northern families who settled in the south, the frequency of war, and the difficulty of the hilly terrain. It was only with the introduction of a new style of plow in the eighth and ninth centuries that ox-drawn plows become commonplace in the south, as noted by Lu Guimeng and several Buddhist writers. This advance allowed the region to become the food-producing center and the economic mainstay of the empire.
A key feature of the new plow was its ability to work a variety of soils, owing to a device that allowed the plowman to alter the depth of the furrow as desired. The plow’s ability to dig deep made it useful for cutting the roots of bushes and wild grasses that had to be removed before new land could be put under cultivation. This was especially important in the middle and lower Yangzi, where unexploited terrain was still available.
The adjustable depth also made it efficient both in the muddy, heavy soils of newly drained areas or rice fields and the sandy soils of coastal regions and riverbanks. Plowing mud in the south required less pulling power than did hardened dry soil, so only one ox or water-buffalo was needed, rather than the three or four customary in the north. Nevertheless, the most common pattern in the south was to use two oxen. This type of plow remained the dominant form throughout the history of late imperial China.
To be pulled effectively, the new plow required major innovations in the methods of harnessing. The long, straight beam that had previously attached the plow to the oxen’s yoke had to be replaced by one that was shorter, although not yet as short as in later centuries. This beam was linked not at the yoke but at a pivoted crossbar (known as a whipple tree) behind the ox. Two cords that ran to either side of the animal joined the bar to the yoke. The yoke itself was significantly curved, individually fitted to each animal, and secured in place by a throat band.
The resulting ensemble had several substantial advantages. First, it could be used to harness almost any number of animals, depending on the soil type and terrain. Second, because the harness did not slip, chafe, or catch at the ox’s throat, an animal could pull harder without difficulty. Third, the shorter beam not only significantly reduced the weight but gave the ox and plow a much tighter turning radius, which allowed the plowman to switch directions or maneuver easily in any shape or size of field.
This new maneuverability was especially important in small, irregularly shaped rice fields and on sloping fields, where one ox could pull a plow up and down steep inclines. Agriculture was thus no longer restricted to flat plains or terraces of friable soil, as in the north, but could be expanded across the hilly terrain that characterizes most of southern China. Although hillsides would not be fully exploited for agriculture until the introduction of American food crops in the sixteenth century, the new plowing ensemble brought some hills into systematic cultivation for the first time.
The most important contribution of the new plow was to greatly improve the preparation of rice paddies in the south, where the goal was to produce a layer of puddled mud at the surface of the field and a compacted hardpan below it to prevent water from soaking into the ground. This required the farmer to guide his ox (or, more commonly, buffalo) back and forth across the field, which was usually cut in an irregular shape to fit the lay of the land. The animal’s hooves packed down the hardpan, making it more impermeable, while the plow progressively pulverized the upper layer of soil. Next, a roller created a smooth finish to the mud that made rice planting easier. In contrast with dry land, each year of plowing a southern paddy field improved its productivity.
After a dry field was plowed, an ox-drawn harrow prepared it for planting by breaking up the remaining clods of earth and smoothing the ground. In the ninth century, farmers in the Yangzi delta developed a new deep-toothed harrow that was much more effective at this task than earlier models. Stone rollers were also used on dry fields, as were wooden rollers with and without spikes. In north China, the old-style Han plow was combined with a new model of seed drill to increase the efficiency of planting.
By Song times this device had been widened to cut and sow four furrows simultaneously. It was attached to a container that automatically fertilized the seeds with sieved manure or silkworm dung as it planted them. In this way, the north, too, expanded its production, although not to the degree achieved in the south. The relative scarcity of human labor in the Yangzi region during the Tang dynasty created ideal conditions for the widespread use of draft animals in the many tasks associated with cultivation. But once the population in the region became extremely dense and the cost of human labor plummeted, the economic advantages of draft animals vanished. During the Ming and Qing dynasties, the use of oxen in southern agriculture steadily declined.
In addition to new seed preparation, new fertilizers, and new oxdrawn equipment, another major innovation in the Tang was the introduction of new varieties of plants that allowed for the possibility of multiple cropping. While more than one crop in a single year remained unusual until the Song, three crops within two years were common by the middle Tang in much of China. In the north this was achieved by alternating summer millet, winter wheat, and then again summer millet. In the south, it consisted of three crops of rice. In addition, vegetables and beans were interplanted with the major grains, both to provide variety in the kitchen and to enrich the soil. In the later Tang and the Song there was also an increase in the range of rice seeds with more desirable properties that facilitated multiple cropping. The most famous of these was Champa rice from central Vietnam, which was first introduced into China in the tenth century and widely adopted at the order of the Song Emperor Zhenzong in the eleventh.
He obtained a variety from what is now Fujian in the far southeast in 1012 a.d. and disseminated it throughout the lower Yangzi. This rice, with its low gluten content, was unusually drought resistant, ripened faster than the old Chinese varieties, and could be grown on poorer soils than high gluten rice. Its defects were that it produced lower yields per plant, was tough to eat, and was more prone to spoilage. Tang farmers probably initially planted it as a form of insurance against droughts. At this time farmers in the lower Yangzi already divided their rice into early- and late-ripening varieties, but the truly early-ripening varieties provided by Champa rice were not in regular use during the Tang.
However, through selective breeding over the decades, farmers produced numerous new strains of rice that combined and improved on the virtues of the older ones. By the twelfth century, dozens of varieties of rice—most of them derived from Champa rice—were available, and all the strains in use before the middle Tang had disappeared. South China was gradually covered with a complex, variegated pattern of cropping that was carefully adjusted to the different soils, climatic conditions, and economic circumstances of each locality. Combining early-ripening and late-ripening rice allowed agricultural work to be spread more evenly over the year, reducing the problem of seasonal unemployment and the risks from bad weather; if one crop was lost, the next might still be saved.
Farmers of the lower Yangzi further expanded their productivity by bringing northern crops such as wheat, millet, and barley into drier areas of the south. The southward migration of wheat started during the period of disunion but became significant only under the Tang. By the Song it had transformed the southern economy. Writing in the late tenth century, Yang Yi described how in one area of the Yangzi drainage basin people survived the failure of the rice crop because good spring rains allowed a bountiful harvest of wheat and millet.
In some areas of the south, Song landlords based their rent on just the rice yield, leaving the wheat crop entirely to tenants for their subsistence. However, alternating wet rice with wheat on the same field was extremely labor-intensive, because rice paddies had to be thoroughly drained before wheat could be planted. Many landlords tried to block the alternation of these crops, believing that it reduced the productivity of the fields as well as that of the peasants who worked them.
While improvements in agriculture—ranging from better seed preparation to multiple cropping—were essential for the productivity gains that underlay China’s medieval economic revolution, the Tang’s greatest achievement was better water control for irrigation, flood prevention, and land drainage. In the north, canals that followed the contour of the land carried water from tributaries of the Yellow River to agricultural land further downstream. In the extensive areas where irrigation canals did not reach, water had to be drawn from deep wells.
The Yellow River itself often ran low during the early summer, when water was needed for agriculture, while substantial dikes were needed to contain potential floods during the irregular downpours of late July and August. Both the dikes of the Yellow River and the irrigation channels of its tributaries were built and maintained by the state. In the south, by contrast, water control was primarily the responsibility of wealthy landowners. The challenge was to drain swampy lowlands for agricultural use and manage the water from mountain streams through the use of dams and dikes. In general, in the drainage basin of the Huai and Si Rivers in central China, large reservoirs were formed by damming rivers, whose water was released through sluices into channels that directed its flow into fields. In the Yangzi drainage basin, on the other hand, the land tended to be either flat and swampy or very hilly.
In both cases, water was collected—either by diversion in the hills or drainage in the lowlands—into artificial pools or tanks that were built by wealthy individual families or by small groups of a few dozen households. Such tanks were already in use in the Han dynasty, but they became widespread in the Tang. The single greatest area of agricultural expansion during the Tang dynasty was the marshy land around Lake Tai and Lake Dongting. The key technology for reclaiming this land was the “polder” field (though “encircled fields” and “counter fields” used a similar approach).
Dikes were built in a large ring to hold back the water at a higher level than the field they surrounded, and sluice gates in the embankment walls controlled the amount of water that was allowed to flow in to irrigate the field. Polder fields probably existed even in pre-imperial times, but they seem to have been widely used only in the Tang. The acreage recovered from lakes and river basins through the use of embankments like these increased enormously in the ninth and tenth centuries, and by the twelfth century the whole Yangzi delta was covered with polder fields. These represented a substantial advance in technology, with large numbers of sluice gates that were capable of draining off the exact amount of water needed at precisely the time that it was required.
Some were sponsored by the government and reached twenty-eight miles in circumference, but most were smaller and belonged to private estates. If the soil was too swampy to be drained, farmers constructed “frame fields,” which were floating wooden frames covered with mud and aquatic plants (usually zizania). Seeds were planted in the soil on top of the frame, which rose and fell with the water level, so that the frame field was supposedly never plagued by flooding. Guo Pu described such fields in a poem written in the early fourth century:
"Covered with an emerald screen,
They drift buoyed up by floating zizania.
Artlessly the seeds of canopied cereals are scattered,
And fine rice plants thrust up of their own accord."
The consequence of these new techniques and the wider extension of older ones was a massive increase in the amount of land being worked throughout southern China and in its productivity. The areas around Lakes Tai and Dongting were brought completely under cultivation, and major inroads were made into regions further south and west. The area around Suzhou, which in the southern dynasties had remained largely unexploited, became a center of agricultural productivity. The mountain valleys of what is now Fujian were also developed. Not only were the number and distribution of these irrigation works far greater than in the preceding period, but the scale of the individual projects was also much larger.
Both drainage and irrigation benefited from the introduction of several devices for moving water. The simplest of these was the counterbalanced bucket or well-sweep. The noria was a wheel with bamboo tubes that filled with water at the bottom of the rotation and then emptied it into an aqueduct at the top. It was useful only in hillier country where streams moved with sufficient velocity to turn the wheel. Elsewhere, farmers relied on the more mobile and adaptable treadle-pallet pump, which required human (or sometimes animal) labor to turn a wheel that carried tubes or pallets from the stream or pond to the aqueduct. All of these devices developed under the Tang, though they were not widely used in agriculture until the tenth century.
The development of woodblock printing in the Tang also made a major contribution to agricultural innovations, as printed manuals helped to disseminate new farming techniques among literate landowners. The Tang government produced the first printed manual on agriculture, and the Song government sponsored editions of the 'Essential Methods of the Common People' and the 'Key Points for the Four Seasons' (Si shi zuan yao), the two greatest agricultural manuals produced to that date. Newer instructional manuals were also composed, and in the Song they were accompanied by illustrations. Local officials distributed briefer printed manuals, often illustrated, to farmers in their vicinity in order to propagate the latest agricultural techniques.
By Mark Edward Lewis in the book 'CHINA’S COSMOPOLITAN EMPIRE' - The Tang Dynasty, The Belknap Press of Harvard University Press, 2009, p. 129-136. Digitized, adapted and illustrated to be posted by Leopoldo Costa.
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