Influence of nitrogen and potassium nutrition on physiological traits and yield of aerobic rice (<i>Oryza sativa</i> L.) variety Vaishak and Aiswarya under heat stress during the flowering stage

Rising atmospheric temperatures due to global warming are expected to negatively affect crop growth and yield, particularly in tropical regions. A field experiment was conducted during the summer seasons of 2022 and 2023 at the College farm, Kerala Agricultural University, Thrissur, to evaluate the response of rice varieties (Vaishak and Aiswarya) to heat stress (2–3°C above ambient) during the flowering stage under aerobic conditions with varying nitrogen (N) and potassium (K) levels. The study employed a Randomised Block Design (RBD) with eight treatments and three replications. The Vaishak and Aiswarya varieties were each tested with three N-K levels (60:30, 90:45, and 120:60 kg/ha) under heat stress, and a control was maintained under ambient temperature. Results showed that Vaishak receiving 120 kg N and 60 kg K2O under stress recorded the highest physiological performance in both years: photosynthetic rate (11.09 and 9.30 µmol/m²/s), stomatal conductance (0.778 and 0.653 mol H2O/m²/s), relative water content (96.68 and 81.14%), soluble protein (23.45 and 19.68 mg/g), proline (95.69 and 80.31 µmol/g), and SOD activity (0.329 and 0.276 g/min). Grain yield was also highest under this treatment, reaching 3602 and 3256 kg/ha in 2022 and 2023, respectively. These results indicated that application of 120 kg N and 60 kg K2O in the variety Vaishak enhanced physiological resilience and yield of aerobic rice under heat stress, and can be recommended as a suitable nutrient management strategy for aerobic rice under changing climate conditions.