As already mentioned, the Ming had to keep a large army along the northern frontiers. But they also had to keep armies in south China, especially in Yuennan. Here, the Mongol invasions of Burma and Thailand had brought unrest among the tribes, especially the Shan. The Ming did not hold Burma but kept it in a loose dependency as "tributary nation". In order to supply armies so far away from all agricultural surplus centres, the Ming resorted to the old system of "military colonies" which seems to have been invented in the second century B.C. and is still used even today (in Sinkiang). Soldiers were settled in camps called _ying_, and therefore there are so many place names ending with _ying_ in the outlying areas of China. They worked as state farmers and accumulated surplusses which were used in case of war in which these same farmers turned soldiers again. Many criminals were sent to these state farms, too. This system, especially in south China, transformed territories formerly inhabited by native tribes or uninhabited, into solidly Chinese areas. In addition to these military colonies, a steady stream of settlers from Central China and the coast continued to move into Kwangtung and Hunan provinces. They felt protected by the army against attacks by natives. Yet Ming texts are full of reports on major and minor clashes with the natives, from Kiangsi and Fukien to Kwangtung and Kwanghsi.

But the production of military colonies was still not enough to feed the armies, and the government in Chu's time resorted to a new design. It promised to give merchants who transported grain from Central China to the borders, government salt certificates. Upon the receipt, the merchants could acquire a certain amount of salt and sell it with high profits. Soon, these merchants began to invest some of their capital in local land which was naturally cheap. They then attracted farmers from their home countries as tenants. The rent of the tenants, paid in form of grain, was then sold to the army, and the merchant's gains increased. Tenants could easily be found: the density of population in the Yangtze plains had further increased since the Sung time. This system of merchant colonization did not last long, because soon, in order to curb the profits of the merchants, money was given instead of salt certificates, and the merchants lost interest in grain transports. Thus, grain prices along the frontiers rose and the effectiveness of the armies was diminished.

Although the history of Chinese agriculture is as yet only partially known, a number of changes in this field, which began to show up from Sung time on, seem to have produced an "agricultural revolution" in Ming time. We have already mentioned the Sung attempts to increase production near the big cities by deep-lying fields, cultivation on and in lakes. At the same time, there was an increase in cultivation of mountain slopes by terracing and by distributing water over the terraces in balanced systems. New irrigation machines, especially the so-called Persian wheel, were introduced in the Ming time. Perhaps the most important innovation, however, was the introduction of rice from Indo-China's kingdom Champa in 1012 into Fukien from where it soon spread. This rice had three advantages over ordinary Chinese rice: it was drought-resistant and could, therefore, be planted in areas with poor or even no irrigation. It had a great productivity, and it could be sown very early in the year. At first it had the disadvantage that it had a vegetation period of a hundred days. But soon, the Chinese developed a quick-growing Champa rice, and the speediest varieties took only sixty days from transplantation into the fields to the harvest. This made it possible to grow two rice harvests instead of only one and more than doubled the production. Rice varieties which grew again after being cut and produced a second, but very much smaller harvest, disappeared from now on. Furthermore, fish were kept in the ricefields and produced not only food for the farmers but also fertilized the fields, so that continuous cultivation of ricefields without any decrease in fertility became possible. Incidentally, fish control the malaria mosquitoes; although the Chinese did not know this fact, large areas in South China which had formerly been avoided by Chinese because of malaria, gradually became inhabitable.

The importance of alternating crops was also discovered and from now on, the old system of fallow cultivation was given up and continuous cultivation with, in some areas, even more than one harvest per field per year, was introduced even in wheat-growing areas. Considering that under the fallow system from one half to one third of all fields remained uncultivated each year, the increase in production under the new system must have been tremendous. We believe that the population revolution which in China started about 1550, was the result of this earlier agrarian revolution. From the eighteenth century on we get reports on depletion of fields due to wrong application of the new system.

Another plant deeply affected Chinese agriculture: cotton. It is often forgotten that, from very early times, the Chinese in the south had used kapok and similar fibres, and that the cocoons of different kinds of worms had been used for silk. Real cotton probably came from Bengal over South-East Asia first to the coastal provinces of China and spread quickly into Fukien and Kwangtung in Sung time.

On the other side, cotton reached China through Central Asia, and already in the thirteenth century we find it in Shensi in north-western China. Farmers in the north could in many places grow cotton in summer and wheat in winter, and cotton was a high-priced product. They ginned the cotton with iron rods; a mechanical cotton gin was introduced not until later. The raw cotton was sold to merchants who transported it into the industrial centre of the time, the Yangtze valley, and who re-exported cotton cloth to the north. Raw cotton, loosened by the string of the bow (a method which was known since Sung), could now in the north also be used for quilts and padded winter garments.