Effects of Environmental and Technical Factors on Rice Yield in Rain-fed Paddy Fields of Northeast Thailand

Relationship between rice yield and several factors which would be concerned with variability of rice yield for rain-fed paddy field in Don Daeng village in Northeast Thailand was discussed. In 1981, a drought year, the mean value of yield of the upper topographically paddy field was only 63% compared to that of lower paddy field. Water condition was the most dominant factor affecting rice yield. Three factors, water condition, soil fertility and varieties cultivated, explained 45% of yield variation among paddy fields in evaluation using quantification scaling type I. In 1983, a bumper year, two factors, fertilizer application and crops in the former year, and above 3 factors could explain only 17% of grain yield variation. On the other hand, these five factors could explain 47% of variation of straw weight per unit area. Partial correlation coefficient between soil fertility and straw weight was the highest value among those between other factors and straw weight. Adoption of improved variety may be usefull for increasing yield, as well as establishment of irrigation facilities.