"Ever-normal granaries" (changpingcang 常平倉) were in imperial times created with the aim to control grain prices. After bad harvests, grain stored in the granaries was thrown (tiao 糶) on the local market to keep the price low, while in years of bumper harvests, grain was taken out of the local market and stored (di 糴, see pingdi pingtiao 平糴平糶) for coming years.
The system originated in the regional state of Wei 魏 during the Warring States period 戰國 (5th cent.-221 BCE), where Counsellor Li Kui 李悝 invented the so-called pingdi system 平糴法, which worked in the way just described. A similar method was applied by Fan Li 范蠡 and is described in the book Guanzi 管子.
During the reign of Emperor Wu 漢武帝 (r. 141-87 BCE) of the Han dynasty 漢 (206 BCE-220 CE), the Chamberlain for the National Treasury (dasinong 大司農) Sang Hongyang 桑弘羊 (152-80 BCE) created the "Balance Law" (pingzhunfa 平準法) by which the government interfered into the market by purchasing or selling certain commodities, including such counting as money, like textile fabric, and money itself. This is perhaps the first instance of monetary policy in China. Geng Shouchang 耿壽昌, the Vice Chamberlain, extended the "Balance Law" to grain prices during the reign of Emperor Xuan 漢宣帝 (r. 74-49 BCE). At that time, bumper harvests over several years had brought down the market price for grain (to 5 qian 錢 per shi 石, see weights and measures) so that peasants did "not earn enough" (nongmin shao li 農人少利). Geng had granaries built in such places, and the government purchased large amounts of grain (400,000 hu 斛) to raise prices. In the years 57 and 56 BCE, Geng ordered to purchase grain from districts located in what is today southern Shanxi instead of shipping it from the southeast (see grain transport). In this way, he saved fifty per cent expenditure. Based on this positive experience, he suggested to build state granaries all over the empire, particularly in the northeastern border regions. They were given the name changpingcang because they balanced out (ping 平) price fluctuations over long periods (chang 常).
Yet there were also critics arguing that the system was harmful to the people, particularly in times when the government purchased low-price grain to boost the price. In the early Eastern Han period 東漢 (25-220 CE), Liu Ban 劉般 (20-79 CE) even enforced the abolishment of the system for some time.
During the period of division 南北朝 (300~600), the granary system was irregularly applied, for instance, in 268, with the aim to regulate the price of rice, millet and textiles, or in 488, when an empire-wide purchase of grain was carried out in the empire of Southern Qi 南齊 (479-502). In the same year, the Northern Wei empire 北魏 (386-534) promulgated a law ordering the local governments to add twenty per cent of grain to the markets in years with high prices. In 564, the method was also applied in the Northern Qi empire 北齊 (550-577).
The Sui dynasty 隋 (581-618), which reestablished rule over all of China, created a central Stabilization Fund Office (changpingjian 常平監, during the Tang period called changpingshu 常平署) in the capital, and built granaries in the prefecture of Shaanzhou 陜州. In 583, Minister of Revenue (duzhi shangshu 度支尚書) Zhangsun Ping 長孫平 initiated a law ordering the populace to take by themselves precautions for bad years by building so-called charity granaries (yicang 義倉).
The Tang dynasty 唐 (618-907) extended in 628 the use of charity granaries all over the country. Every farmer household had to deliver 2 sheng 升 of grain per mu 畝 of land to be stored in these granaries. In 639, the system of ever-normal granaries was revived in several prefectures and the two capitals Chang'an 長安 (present-day Xi'an 西安, Shaanxi) and Luoyang 洛陽 (today in Henan). They were supervised by officials of the Stablization Fund Office (pingshu guan 平署官). In 719, ever-normal granaries were built in more regions, and a law decreed their holdings: Granaries in populous prefectures were to hold grain with a value (or be able to purchase grain with a value) of 3,000 strings (guan 貫) of cash, mid-size prefectures 2,000, and smaller prefectures holdings of 1,000 strings. The price at which the authorities were ordered to purchase rice was also fixed at 3 qian per shi. In 749, the granaries of the ten circuits of the Tang empire held together 4.6 million shi of grain (Ning et al. 1992).
The rebellion of An Lushan 安祿山 (703-757) shattered the granary system, but it was revived in 780. Vice Minister of Revenue Zhao Zan 趙贊 suggested to create a granary budget in all important cities and places which was to be fed by custom fees paid by itinerant merchants and from the taxes levied on bamboo, timber, tea, lacquer, and other commodities. Yet in the end, those new taxes were consumed by military expenditure. An edict from 806 decreed that twenty per cent of the annual harvest was to be stored in ever-normal or charity granaries. Both types of granaries were from then on part of a unified granary system (changping-yi cang 常平義倉). The 806 edict was thirty years later renewed by the order to levy, apart from the field tax (tianfu 田賦), a granary tribute of 1 sheng of grain per mu of land.
The Song dynasty 宋 (960-1279) adopted this system and built first granaries in the capital Kaifeng 開封 (today in Henan), and after 1006 all over the empire. The holdings of the granaries were determined by the size of the population in each prefecture. The budget to purchase grain (diben 糴本) ranged from 2,000 to 12,000 strings of cash. Each year in autumn, when the grain flushing to the markets dumped the price, the government purchased so much that it was raised by 3 or 5 wen 文 (i.e. qian [per sheng]), and in times of high grain prices, the granaries were opened to lower the price, but not lower than an average price (benqian 本錢).
If there was no need to throw grain on the market for several years, the old stocks had to be changed out. The system was in fact so effective that for many years, the grain earmarked for the granaries could be spent for the salaries of state officials or the pay of troops. In 1069, during the reform period under Counsellor-in-chief Wang Anshi 王安石 (1021-1086), the granary system was replaced by the green-sprouts law (qingmiaofa 青苗法), according to which peasants were given credit twice a year before the harvest set in. The money formerly used to purchase grain, with a total volume of 15 million strings (Ning et al. 1992), served to grant those credits (qingmiao benqian 青苗錢本). Five years later, this method was mixed with the old one, and half of the amount formerly requested for the granaries was collected in this way. In 1076, the value of grain in the granaries amounted to 37.39 million strings (Ning et al. 1992). The Southern Song 南宋 (1127-1279) renewed the system. In 1167, the amount of grain stored in all ever-normal granaries of the empire was 35.79 million shi, with a value of 2.87 million strings of cash. Yet such figures must be taken with care, as there are examples that records in local grain registers surpassed figure reported to the central government by fifty per cent and the real holdings by nine hundred per cent (Ning et al. 1992).
The Jin dynasty 金 (1115-1234) also adopted the granary system, with a quota of 20 per cent from the harvest in rich yearch. In 1190, it was revised, and Emperor Zhangzong 金章宗 (r. 1189-1208) decreed that granaries had to provide so much grain as would suffice to nourish the prefectural population for three months. The observation of the administrative rules were strictly to be observed, for which purpose the court sent out inspecting officials. Districts with more than 20,000 households were expected to hold 30,000 shi of grain, and small districts with less than 5,000 registered households, only 5,000 shi (Chen 1992). In 1195, the holdings of the 529 granaries in the Jin empire were 37.86 shi of grain (Ning et al. 1992).
The granary system introduced in 1257 by the Yuan dynasty 元 (1279-1368) was soon abolished, but revived in 1271. The local authorities were ordered to purchase grain at 20 per cent of the market price (shijia 時價). This time, the state granaries held 800,000 shi of grain. The overseers of the granaries were selected from the local population and were for their services freed from duties like the corvée. In 1309 the empire-wide building of granaries was decreed, and each granary was administered by three state employees. Through the whole Yuan period, the granary system did not really work, and embezzlement was widespread.
The Ming dynasty 明 (1368-1644) changed the old system and invented new procedures. One "provisional granary" (yubeicang 預備倉) served four townships (xiang 鄉). The local government issued certificates when purchasing or collecting grain. In years of famine, the granaries lend grain to the farming people, but the government requested back payment with the next harvest.
The Qing 清 (1644-1911) created a new type of granary, namely the community granaries (shecang 社倉) which were to support the network of charity and ever-normal granaries. The amounts held by these granaries were minutely reported to the Ministry of Revenue (hubu 戶部). The flow of grain into and out of the granaries was also exactly regulated, with output during spring and summer, and collection of grain during the harvest period. In years with bad harvest, grain was thrown on the market for famine relief (zhenji 賑濟). For lending out grain in spring, the granaries requested an interest rate of 10 per cent. As in earlier ages, exact rules determined what amounts of grain a district of a certain population size was to store. The granary system operated according to the formula "[grain remains] in the place of origin" (yong liu ben jing 永留本境), in order to prohibit the sale of grain by district magistrates to other districts, where a better price would be obtained. Yet in practice, such arbitrage operations were quite common. Sometimes local granaries had the problem that peasants refused to sell their harvest to the granaries, so that magistrates had to "urge for contributions" (quan shu 勸輸) to the public.