八-一三世紀江南の潮と水利・農業

Abstract

Due to the flatness of the Jiangnan moor, the ebb and flow of strong saltwater tides from the coastal region, influenced waterways and channels deep into inland areas. This paper discusses the effects of the salt tides of the Wusongjiang, the largest river of the Jiangnan area, on irrigation and farming, during the time when they reached the Taihu. Since salt tides entered the coastal regions, defensive embankments were constructed around the area of Hangzhou to protect the agricultural industry from the effectsof salt water. Nevertheless, as late as the twelfth century salt water tides entering through waterways and channels did extensive damage to the agricultural industry in Xiuzhou. In controlling the extent of that damage, dams and embankments played a major role. From the fourteenth century on, the entire coastal area around Hangzhou and Xiuzhou which faced the sea south of Wusongjiang, were completely isolated from coastal areas by means of dams and embankments. The tides carried large quantities of earth and soil which tended to block up waterways and channels. While the dredging of clogged waterways to protect the agricultural industry from flooding and drought damage became important undertakings, and flourished to an extent, still the problem of blockage was never fully eliminated. Apart from maritime areas, the tides which reached inland areas were fresh water tides. By using the fresh surface water from these tides, irrigation was practiced. While dredging and irrigation gradually diminished the influence of saltwater upon inland agricultural industries to the extent that they were no longer needed, during this period, dredging and fresh water tidal irrigation were still widely practiced in inland areas. With the expansion of areas in which the damaging effects of salt water tides were not present, the use of river slush as an effective fertilizer developed. In Jiangnan the use of such fertilizer contributed to the development of its productive capacity. Thus, the construction of embankments to keep salt wate out and dredging to clear clogged waterways reordered the natural effects of salt on agriculture so that, along with the use of riverbed slush fertilizer, they provided fundamental elements in the development of Jiangnan agriculture.