Tribute grain (caoliang 漕糧 or 漕粮) served in imperial times to feed the officialdom and the court in the imperial capital, as well as the troops in military garrisons in and around the capital region and in border regions. The tribute grain was a type of tax replacing the common field tax (tianfu 田賦) delivered in kind, but was only applied to regions of rich harvest, mainly in the lower Yangtze area. It was mainly transported by river (shuiyun 水運) along the Grand Canal (da yunhe 大運河; compare the character 漕 with the water radical), but in certain periods of history also by the sea (haiyun 海運).
The earliest evidence for the tribute grain is an event in 486 BCE, when the regional state of Wu 吳 fortified the city of Han 邗 (today's Hanjiang 邗江, Jiangsu) and connected it by canals with the River Huai 淮河 and the Yangtze. During the Western Han period 西漢 (206 BCE-8 CE) grain (millet, su 粟) was shipped from the Shandong Peninsula westwards along the Yellow River and up the River Wei 渭水 to the capital Chang'an 長安 (today's Xi'an 西安, Shaanxi). At that time the salaries of state officials were paid out in grain, and not in money. During the time of Emperor Xuan 漢宣帝 (r. 74-49 BCE) as much a 4 million hu 斛 (= 2 million shi 石 "bushels", see weights and measures) were brought to the capital. For this enterprise, as much as 6,000 troops (zu 卒) were needed. The grain was stored in large granaries in important nodal points. During the Qin period 秦 (221-206 BCE) the Aocang Granary 敖倉 had been built in Chenggao 成皋 (today's Yingyang 滎陽, Henan), and the Han dynasty created a network of imperial granaries (taicang 太倉).
The Sui dynasty 隋 (581-618) built granaries in Liyang 黎陽, Heyin 河陰, Changping 常平 and Guangtong 廣通, others granaries were called the Luokou Granary 洛口倉 and Huiluo Granary 回洛倉. During the Sui period the Grand Canal was built which connected the Yellow River with the River Huai and the Yangtze. The origin of grain during that time was shifted from the eastern parts of the Yellow River plain to the lower Yangtze region. The Grand Canal made it possible to ship as much as 3 to 4 million shi of grain to Chang'an.
The Northern Song 北宋 (960-1126) chose Bianjing 汴京 (Kaifeng 開封, Henan) as their capital. It was located much more east than Chang'an and therefore made transport easier because the dangerous rapids in the Sanmen Gorge 三門峽 could be avoided. For the supply of Kaifeng, the four rivers Bian 汴水, Yellow River, Huimin 惠民 and Guangji 廣濟 were connected with each other. An amount of between 4 and 7 million shi of "government grain" (guanliang 官糧) were brought to the capital, but also to military garrisons in the border regions. In order to guarantee the supply with a sufficient amount of rice, the Song government fixed quota of rice to be annually delivered as tribute grain. It also provided an exact schedule to which destinations the grain was to be brought to. In this way, the grain tribute system changed from a general system of grain supply into an elaborated tax system. This tendency was influenced by the increasing monetization of the economy during the Song period, in which more exact data were needed as to the economical potential of the different parts of the empire.
In the early Ming period 明 (1368-1644) the total amount of the tribute tax quota to be brought to the capital was fixed at 3 million shi per year. The Ming capital was first Nanjing 南京 (today in Jiangsu), which is very close to the area where most of the tribute grain came from, but then Beijing in the far north was made capital. The transport therefore had to rely on a new canal system through the Shandong Peninsula whose foundations had been laid during the Yuan period 元 (1279-1368). In 1472 the central government ordered that an annual quota of 4 million shi of tribute grain was to be delivered by the provinces of Jiangsu, Zhejiang, Anhui, Hunan, Jiangxi, Hubei, Henan and Shandong. The Qing dynasty 清 (1644-1911) largely followed the tribute grain concept of the Ming, but ordered that a certain amount of the tribute grain was to stay in the provinces of origin, to stock the local reserve granaries.
Apart from the tribute grain, the Ming and Qing levied a specialized type of grain, the so-called "white grain" (bailiang 白糧). It originated in the prefectures of Suzhou 蘇州, Songjiang 松江, Changzhou 常州, Jiaxing 嘉興 and Huzhou 湖州. 170,000 shi of rice and glutinous rice ("sticky rice") were levied to supply the imperial palace, and a further amount of 44,000 shi of unhusked rice (caogengmi 糙粳米) to supply the offices of the central administration.
The population of the regions from where the tribute rice came were also liable for delivering several types of additional volumes of grain to cover the transport expenses. These fees were called haomi 耗米, qingji 輕賫, zengtie 贈貼 or ximu 席木, and summarized under the names caoxiang 漕項 or suicao 隨漕. The height of the transport surcharge was as high as about 1.7 dou 斗 per shi of rice (i.e. 17 per cent), but it was also collected in money instead of in kind. It was a main source for exploitation and embezzlement by the local officialdom who managed the collection of this money.
The increasing commercialization of the economy initiated a trend towards the replacement of tribute grain by the substitutive payment of money called zhecao 折漕 or caozhe 漕折. It was easier for the local officials to collect money instead of rice. With the collected money they commissioned merchants to buy rice and to ship it to its destination. This custom originated in the so-called "method of adjusting the tribute grain tax" (pingmifa 平米法) intiated by Zhou Chen 周忱 in 1433, and was first only applied to the transport surcharge. In 1436 it was decreed that not more than 1 million liang (tael) of money was to be collected as a substitution for rice, yet in the late years of the Ming period the amount of grain transported by the government itself was only a small proportion of the whole tribute grain. The Qing dynasty first prohibited the substitution of rice by money, but was then forced by the local officialdom to meet the demands of practicability. In the late nineteenth century most provinces of origin were allowed to collect the total amount due in money. The conversion rate was at that time 1 liang per shi of rice. The only exception were Jiangsu and Zhejiang which still had to deliver an amount of 1 million shi of grain. Yet in general the tribute grain transport system came to a halt and was abolished in 1901.