INFLUENCE OF SOLAR-RADIATION AND TEMPERATURE ON IRRIGATED RICE GRAIN-YIELD IN BANGLADESH

Results are presented from several shading and time-of-planting experiments to investigate the effects of total incident solar radiation (irradiance) and temperature on irrigated rice grain yield in Bangladesh. The substantial influence of irradiance in the reproductive (panicle initiation to anthesis) and ripening periods (anthesis to maturity) on yield and yield components is demonstrated. In all experiments where radiation varied substantially there was a linear relation between grain yield and irradiance during the reproductive and ripening stages. In contrast, grain yield was negatively correlated with mean temperature during the 30 days preceding anthesis. The effects of temperature and irradiance could be combined by the use of the photothermal quotient (Q, ratio of mean daily irradiance to mean temperature above a base temperature), which explained most of the variation in grain yield for any one cultivar with different amounts of shading and different planting dates. The relation between Q and yield varied between varieties because of differences in spikelet numbers. grain weight and percentage sterile spikelets, as well as other unidentified factors. The relation also varied significantly between seasons for one of the three varieties for which data were available. The mean annual time course and variation of Q were calculated for Jovdebpur, and the yield of trial plots related to it.