Assessment of Thermal and Radiation Use Efficiency of Rice (CO 47) Across Seasonal Sowing Windows in Coimbatore, Tamil Nadu

Understanding seasonal energy subtleties is essential for optimizing rice cultivation under changing climatic conditions. This study evaluates the thermal and radiation use efficiency of rice variety CO 47 across seven major sowing windows, Navarai, Sornavari, Kar, Kuruvai, Samba, Thaladi, and Late Thaladi, in Coimbatore district, Tamil Nadu. Using 21 years (2004–2024) of daily climatic data from NASA POWER, thermal indices such as Growing Degree Days (GDD), Photothermal Units (PTU), and Heliothermal Units (HTU) were computed alongside derived efficiencies, Heat Use Efficiency (HUE), and Radiation Use Efficiency (RUE), for vegetative, reproductive, and maturity phases. Results revealed that the Sornavari and Navarai seasons exhibited the highest cumulative thermal and radiation indices, supporting robust crop development. Mid-year sowings like Kar and Kuruvai balanced thermal and radiation efficiency, while late Thaladi faced significant climatic constraints, particularly during reproductive stages. HUE peaked in early-season sowings, whereas RUE was highest in mid-year crops. These findings stress the need for seasonspecific agrometeorological strategies to enhance rice productivity and resilience under variable climates.