Effects of Temperature and Soil Water Content during Grain Filling Period on the Yields of Grain Sorghum

Abstract

This experiment was conducted to determine the effects of tempcrature and soil water content during grain filling stage on grain yields in terms of dry matter production, sink capacity of grains and distribution of materials produced of grain sorghum (Sorghum bicolor (L.) Moench). Early hybrid variety, NK129, was seeded in pots in June 3, 1974 and was grown outdoors until the end of flowering. Then the plants were subjected to 35°C/25°C, 30°C/20°C and 25°C/15°C of day/night temperature in the phytotron under natural light conditions during the ripening period. Soil water contents were maintained in moderate water and drought conditions in each temperature. The plants were harvested when seed coat hardened. Results obtained are as follows. 1. Grain yields in the moderate soil water conditions were little affected by temperatures. However, grain yields in drought conditions were reduced at high temperature and the highest yield in drought conditions was obtained at 25°C/15°C. 2. Crop growth rates in moderate water conditions were higher at 35°C/25°C and 30°C/20°C than at 25°C/15°C, but total dry matter accumulation during grain filling pericd did not differ among temperatures because maturing times were prolonged at lower temperature. On the other hand, crop growth rates at 25°C/15°C and 30°C/20°C in drought conditions were higher than at 35°C/25°C, and total dry matter accumulations at harvesting time were the highest at 25°C/15°C and the lowest at 35°C/25°C. 3. Net assimilation rates in moderate water conditions showed the trend of higher values at higher temperatures, but net assimilation rates under drought conditions were higher at 25°C/15°C than at 35°C/25°C. Crop growth rate was positively correlated with net assimilation rate. 4. Sink capacity of grains estimated from weight per 1000-grain at harvesting time was limited by the interaction of high temperature and drought conditions, and it was not affected by low temperature of 25°C/15°C. Early hardening of seed coat is possibly one of the cause of limitation. The greater part of grain yields at 35°C/25°C and 30°C/20°C under drought conditions resulted from materials translocated from vegetative organs to grains. 5. Grain yields were mainly affected by dry matter accumulation during grain filling period, but the contribution of materials translocated from vegetative organs could not be neglected for grain yield under drought conditions. Favorable temperature for grain production will be different with soil water contents. Favorable temperature in this experiment was over a range of 35°C/25°C to 25°C/15°C under moderate soil water conditions, but it was in a little lower range of near 25°C/15°C under drought conditions