Variability of yield and yield components of rice in rain-fed paddy fields of northeast Thailand.

Abstract

Rice production in Northeast Thailand tends to show both low yield per unit land and unstable crops. The objective of this report is to clarify the actual situation of the rice cultivation. One typical rice growing village, Don Daeng which is located l5 km from Khon Kaen city was chosen for the study. A survery of growth of rice, yield and its components was carried out in the village. Thirty one and 30patchs were selected as sample paddy fields in 1981 and 1983, respectively. Rice cultivation of this village depends upon traditional local varieties and rain-fed paddy fields without fertilizer. In 1981, unhusked grain yield was so low as the mean value of 181.6g/m2 due to drought. The yield showed a positive correlation with the each component. On the other hand, in 1983 the yield increased to 236.3g/m2 as the mean value due to enough rain fall, and showed a correlation with the number of panicles per square meter. The growth and yield tremendously fluctuated among paddy fields in both years. The yield correlated positively with the straw weight and the leaf area index, and negatively with the light transmission rate under a plant canopy. Moreover, concentrations of nitrogen, phosphorus and potassium were remarkably low. These results seem to suggest that increases in leaf area index and the number of spikelets per unit area by vigorous vegetative growth lead to a yield increase.