Rice Bran-Coated Urea is Associated with Improved Photosynthetic Stability and Yield Performance in Proso Millet under Heat Stress

Heat stress affects proso millet (Panicum miliaceum L.) production significantly by reducing photosynthetic activity and altering growth processes. This study investigated whether altering nitrogen release dynamics with rice bran-coated urea (RBCU) could increase physiological performance and yield under heat stress in the field. RBCU and mineral-coated urea fertilizers were administered at varying nitrogen rates across two growing seasons, during ideal and high-temperature planting periods. Under summer heat stress, RBCU at 80 kg urea/ha increased carotenoid content and maintained a stable chlorophyll a/b ratio. It also resulted in a distinct oxidative status, where MDA levels—though elevated—remained comparable to or lower than other coated urea treatments and were compatible with sustained physiological activity. RBCU application also resulted in moderate increases in leaf area and panicle length, as well as a minor delay in heading, indicating changes in canopy structure and phenological timing. Under heat stress circumstances, these physiological and morphological responses correlated with increased GY and harvest index. Correlation and regression analyses found strong relationships between GY, photoprotective qualities, and canopy characteristics, implying a coordinated response that is associated with higher production under stress. Overall, the findings suggest that rice bran-coated urea application is associated with greater photosynthetic stability and higher yield in proso millet under high-temperature field conditions.