Evaluation of the Influence of Contrasting Photoenvironments on Paddy Rice Yield in Mountainous Areas of Japan

Abstract

Estimating how light environments shape rice yield is essential for sustaining agriculture in mountainous regions. Over three seasons (2017–2019) we monitored air temperature, photosynthetic photon flux density (PPFD), yield components, and yield in two paddy fields with contrasting light environments in Tokamachi, Niigata, Japan. The lower-light field received 82 of the cumulative PPFD of the higher-light field, yet no significant difference in yield was observed. This result suggests that reduced panicle density under low-light conditions was compensated by increases in spikelets per panicle and grain filling. Our findings indicate that the balance between source and sink, rather than absolute irradiance, is a key determinant of rice yield under complex topography.