Abstract
The constancy of the heat unit accumulation needed for the heading of sorghum cultivar P956 was examined for the simple heat unit accumulation method, the effective heat unit accumulation Method I in which a temperature above 10°C was accumulated, and the effective heat unit accumulation Method II in which the temperature above the minimum growth temperature was accumulated. The minimum growth temperature was calculated by the least squares method from the relation between the days after sowing and the simple heat unit accumulation until the heading date. The results showed that the coefficient of variation, showing the accuracy of the application, was 9.7 to 8.0 % for P956 and the constancy was inferior. In addition, the heading date was predicted by preparing the multiple regression formula using the average temperature and day length after sowing. The results showed that the standard deviation of differences in days between the observed and the estimated by the multiple regression formula, using the temperature for ten days after sowing and the day length at sowing time as variables, was 2.8 days for P956 and the heading date was accurately predicted by this formula.
