東北タイ・ドンデーン村 : 稲作の不安定性 (<特集>東北タイ・ドンデーン村)

Abstract

The rain-fed rice production of Don Daeng village and its surrounding area is extremely unstable. Compared with an exceptionally bumper harvest in 1983, rice production in the preceeding years were 4 percent in 1978 due to flood, 10 percent in 1979 due to drought, 5 percent in 1980 due to flood, 54 percent in 1981 due to light drought in the late growing season, and 18 percent in 1982 due to early-season drought and subsequent local submergence. The production in 1983 alone accounted for more than 50 percent of the total production in these six years. The instability of production was analysed in terms of (1) the variability of rainfall and (2) the distribution of ponded water-depth and soil moisture in paddy plots. The rainfall analysis showed that (i) successful rice production in the western part of the Khorat plateau, where the Don Daeng village is located, is marginal due to scarce rainfall, (ii) seasonal distribution is variable due mainly to unpredictable onset of the monsoon season, and especially to the occurrence of dry spells of highly variable duration and locality, and (iii) rainfall is distributed unevenly over time, e.g., the sum of the 10 largest amounts of daily rainfall accounts for 50-60 percent, and the 3 largest amounts of daily rainfall for 20-30 percent, of the total rainfall in the whole rainy season. By a simple simulation model of water balance in paddy plots, the parameter D_2, which indicates ponded-water holding capacity, was proved to be a good indicator of water conditions of the paddy land. This parameter varies considerably with location, being controlled largely by topo-sequence, and is closely correlated to the yields of rice. Rice production in the individual six years was explained, at least qualitatively, by the corresponding variability of rainfall and water condition in the paddy land. Finally, some implications of the extreme instability of rice culture in the village are discussed : (i) the total absence of modern techniques for intensifying rice culture, though such techniques have been introduced in non-rice farming, (ii) land holding and its inheritance and transaction, (iii) cooperation among kin in rice farming and consumption of rice, and (iv) the traditional village attitude toward emigration in search of better paddy land.