Comparisons of Efficiency of Solar Energy Utilization and Efficiency of Solar Energy Conversion in High-Yielding Rice Canopies

Abstract

Efficiency of solar energy utilization (Eu) and efficiency of solar energy conversion (Ec) were compared and studied for panicle-weight type genotypes developed at the Chugoku National Agricultural Experiment Station, leading cultivars produced in the Chugoku region, and highyielding types developed in other countries. Furthermore, efficiency rates in solar energy utilization and conversion gathered to date have been compared with efficiency rates obtained by this author. Eu ranges from 1.37 to 1.61%, with a high efficiency rate of more than 1.55% were recorded for panicle-weight types Chugoku 113, Chugoku 116 and Hoshiyutaka, Indica-type Tainung 68 and Miliyang 23, and Japonica type Nipponbare and Koganebare. The solar energy utilization rate for grain weight (Eu grain) ranged from 0.48 to 0.75%, with rate of 0.7% or higher for Chugoku 118, Hoshiyutaka, Miliyang 23, Nipponbare and Koganebare. Ec was as high as 2.98, 2.83 and 2.68% for Nipponbare, Hoshiyutaka and Chugoku 118, respectively. The high Ec rate for panicle-weight types is likely to be caused by high radiation absorption, due to high absorption of each genotype, and a high level of total integrated solar radiation. Radiation use efficiency (RUE) was 1.98 g/MJ, 1.97 g/MJ and 1.85 g/MJ for Hoshiyutaka, Nipponbare and Chugoku 118, respectively. The difference was not accepted in the genotypes used for the experiment. In order to raise Ec and RUE, a leaf inclination angle is large and a plant type with the light-intercepting characteristics and high LAI is an ideal. Furthermore, high-yielding productive capacity needs to maintain a high canopy absorption by maintaining the SPAD value of a leaf with the topdressing of a ripening period