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Hani and Yi technique of irrigation has always been a secret since their rice terraced fields were built from mountain top to deep valley. Many friends also wrote me asking for the Hani & Yi method of rice cultivation but not until recently I was lucky to locate a valuable field survey by Adachi Shimpei. I hope his work helpful to all of us who are willing to learn. Today text is continued from yesterday post.



Terraced Rice Cultivation


3. The Cropping Season and Year-round Irrigation

Rice is grown once a year in the wet season. Because of the high altitude, the cropping season for rice is determined by temperature rather than by rainfall patterns, considering that rice plants are often damaged by cold weather both at the beginning and at the end of the growing season. This limitation in the growing season creates a problem for the use of water resources. Irrigation water is most important for land preparation (works such as plowing, repairing dikes and harrowing) before transplanting. However, the land preparation period coincides with the low-water season of mountain streams, which are the major water sources for the paddy fields. As will be discussed later in this section, this imbalance is one of the factors leading to this unique irrigation practice, not to mention the construction of long-distance irrigation channel observed throughout the Ailao Mountains.

One of the most significant features of agricultural technologies in terraced rice cultivation in the Ailao Mountains is the practice of year-round irrigation. Terraced fields are irrigated and kept inundated throughout the year, even in the dry season when no crops are grown. The reasons for this practice may be summarized as follows.

1) To prevent water leakage or the collapse of terraced fields,
2) To prevent soil from becoming too hard,
3) To store water for farming works carried out in the low-water season,
4) To maintain high rice yield.

First of all, deep cracks and fissures develop in the clay soil of the paddy fields when it dries out. This leads to serious water leakage, and in more severe cases, to the collapse of terraces (midede). This problem is not serious for paddy fields in the plains, but is crucial for terraced paddy fields built on steep slopes where the collapse of terrace easily causes large-scale loss of farmland. The second reason is also related to soil properties. Dried clay soil is too hard to plow, and it is very difficult to mix with water. The third reason is related to the first reason. As described above, irrigation water is most needed for land preparation during the driest season of the year. If the fields were left to dry up after the harvest and were then watered again just before land preparations, the scarce water during this season would be insufficient to fill all the terraced fields suffering from severe water leakage. In fact, during the Great Leap Forward (1958-1960), the local government launched a campaign to dry up the terraced fields and grow wheat during the dry season. This experiment led to severe water shortages during the land preparation period and to the collapse of many terraced fields, resulting in a great decrease in rice production. The fourth reason is based on farmers’ answers to author’s question “why do you keep your field flooded during the dry season?” The most common answer was, “if you don’t irrigate, the rice yield will be very poor.” This idea seems to contrast sharply with “the phenomenon of soil drying,” which is widely observed in Japan. The soil drying effect refers to nitrogen mineralization that occurs when the soil is watered after being dried, and is considered to be favorable for the growth of rice. In the Ailao Mountains, however, a different reaction may have a stronger effect, leading to a decrease of the yield. More and in-depth investigation is required to clarify this mechanism.

As for the fourth reason, a kind of paddy fields called mifa provides a good example. Mifa is a terraced paddy field that has no right to draw water from the irrigation channel during the dry season, because the field is newly opened and irrigation water of the channel was already insufficient at the time of construction (a detailed example will be given in the next section). Mifa can be widely observed in the Ailao Mountains. Such semi-rain-fed paddy fields, mifa are distinguished from the paddy fields called mio that can be irrigated throughout the year. Mifa can be irrigated only after the completion of transplanting in all of the mio and the demand for irrigation water relaxes (usually end of May-early June). According to the villagers, the rice yield of mifa is usually smaller and more unstable than that in mio and the dikes of mifa are vulnerable to collapse during heavy rainfall. The yield (t/ha) in mio and mifa estimated by a former village head are: 2.0 and 0.8 on the upper slopes (higher than 1,650 m in altitude) and 3.0 and 1.2 on the middle slopes (1,550-1,650 m in altitude) respectively. On the lower slopes (lower than 1,550 m in altitude), there are only mio (4.8 t/ha). The yield is high in the low altitude fields both in mio and mifa, but it is very clear that the yield in mifa is less than half of that in mio for each altitude level.

In the following part of this paper, the descriptions and discussions will mainly focus on mio, and the term “paddy field” will be used to mean mio. Differences with mifa will be described separately, as required. This is not only because mio is the dominant type of terraced paddy field in the Ailao Mountains, but also because of the importance of mio to farmers. The villagers consider that only mio is a “complete” terraced paddy field and the term “demi” (general term for the paddy field) often refers only to mio in their daily conversation. The word “mio” is used only when they emphasize the difference with mifa, which they considered as “imperfect” or “inferior” paddy field.

4. Irrigation and Drainage in Shanlaoqing Village

As described above, year-round irrigation has helped maintain both the rice yield and the physical structure of the terraces. In this section, an attempt will be made to provide a comprehensive description of the water control and related technologies observed in Shanlaoqing village.

Development of Irrigation Channels

The year-round irrigation, especially the requirement of dry season irrigation has encouraged the development of longer irrigation channels. In the following section, the historical processes associated with irrigation channels will be examined.

According to the elderly villagers, the construction of paddy fields began in the lower slopes (at least 300 years ago). When Shanlaoqing village was founded at its present location, the water of the mountain streams near the village had already been taken by two irrigation channels of the nearby Potou village (also a Yi village but older than Shanlaoqing) to irrigate their terraced paddies. Therefore, the people in Shanlaoqing village had to take their irrigation water from sections of the streams that were lower than the water intakes of Potou village, where the remaining surface water and infiltration water welling up from the riverbed was available. Consequently, at an early stage, most terraced paddy fields in Shanlaoqing village were opened on lower slopes. Some terraced fields were opened with independent short irrigation channels that took water from small mountain streams or springs. It is supposed that when no more land or water was available for new terraced fields on the lower slopes, a 7-km irrigation channel (mozotemoyiro) was constructed under the leadership of the descendants of the village founder in order to expand the paddy fields on the upper slope (at an unknown date). The main water source for this irrigation channel is a stream on the upper slope of Mt. Guanyin (2,662 m) located about 5 km north of Shanlaoqing village. In addition to this, the water of numerous small streams also flows into the mozotemoyiro channel on the way to the village. This mozotemoyiro channel now irrigates about half of the total terraced paddy area in the village.

Shanlaoqing village shows the typical character of water exploitation for terraced field development in the Ailao Mountains. After making use of all the water resources available near the village, water resources in the upper watershed were exploited to enable further expansion of terraced fields through the construction of a longer irrigation channel.

During the agricultural collectivization period (1958-1979), food shortages and the prohibition of side work outside the village led the villagers to expand the paddy fields on the upper slopes. But because irrigation water from the mozotemoyiro channel was limited, the newly opened terraced fields became mifa that cannot take water from the mozotemoyiro channel during the dry season.

By Adachi Shimpei, ASAFAS, Kyoto University

(To be continued)

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