東北タイ・ドンデーン村における天水田稲作の収量(<特集>渡部忠世教授退官記念号 : 熱帯アジアの稲と稲作)

Abstract

Don Daeng village is located near Khon Kaen in Northeast Thailand. Rice production in the village depends on rain-fed paddy fields, and is extremely unstable. This paper discusses its yield variation. At harvest time in 1981 and 1983, paddy yields were estimated by cutting and by standing crop survey. The latter was also done in 1985. For analysis, a computer-compatible data base including field size, landform unit, and cropping calendar was used. Frequency distributions of paddy yield grades differed greatly from year to year, being skewed toward the lower range in 1981 and 1985, when the production was poor, and toward the higher range in 1983, when there was a bumper crop. The maximum yields, however, did not differ from one year to another. In the years of poor harvest, plots at lower elevations gave higher yields than those on higher ground, while there was no difference between them in the year of good harvest. In all years, yields were nearly equal in the lower land; but in the higher land yields increased drastically in the good year. The bumper harvest of 1983 was thus primarily due to a bottom-up effect, the increased yield in normally poor-yielding plots, rather than to a yield increase across all plots. The lower land produced a large amount of paddy not only in the good harvest year but also in the poor harvest years. But in the bumper year the production share of this land was decreased by the increase of production in the higher and middle land.