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 Kwangsi.

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 t