Photographer's Note


*Photo: Hani rice paddies mixed with cloud in Yuanyang, Yunnan Province.

Rice terraces
provide the most spectacular agricultural landscapes in Asia. Here, permanent irrigation has allowed the conversion of slopes along uplands into rice fields and fields of other crops with which the rice crop is alternated. While much of irrigation technology on terraced land is somewhat crude, dependent on mud and brush dams and short distribution canals, some groups of farmers.

Terrace building and water control is a distinctive cultural phenomenon of Asia. Terracing, as done in many parts of Asia, consists of building stone walls, often without mortar, along the slope and contours of uplands being converted into cultivated land. The walls might be given a slight batter (receding upward slope) or inward lean at the top. These walls often exceeded six meters in height and were topped with sluices for water drainage. Earth materials would then be used to fill each unit to a level just below the top of the wall. By then staggering the field units in overlapping manner at different levels, a whole mountain slope might be terraced toward the top such that it resembled a sculptured system of fields covered with rice and other types of crops. The field units may be as narrow as 2.5 meters but as long as 90 meters on steep slopes. They are, however, commonly much wider and not so long. For irrigation, water is usually introduced at the top of a terrace series or sometimes as a complementary supply at an intermediate point. The water that is supplied then moves through sluices in each field by gravity downward across each level of the terrace. Finally, the water empties into a stream channel at the bottom of the valley.

Water control, which is crucial in the use of terraces, consists of careful adjustment of the volume of water in the beginning and, hence, its distribution throughout the system of field units making up the terraced series. The system must therefore be able to bring in the required volume of water at any time during the growing season. The system must also be able to divert excess water at any point at any time.

Terracing of the fields not only served irrigation purposes but also provided a high degree of protection against the ever-present threat of soil erosion as well as loss of soil fertility. In many areas of rice and other crop cultivation using terraced irrigation and such traditional methods of farming, cultivation has continued for hundreds and even thousands of years without any serious erosion or loss of soil fertility. This has been the case particularly in areas where irrigation or floodwaters bring abundant mineral matter and where there is deposited a seasonal layer of fertile silt.

(Yue Choong Kog)


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