Evaluation of drip and flood irrigated treatments under varying heat stress on winter wheat: a four-seasons experimental study

Evaluating and enhancing grain yield (GY) and water productivity (WP) is crucial for ensuring food security while reducing pressure on limited water resources through more efficient water use. This is particularly important when the adverse impacts of climate change are growing, resulting in more frequent heatwaves. However, limited research has examined the response of winter wheat GY and WP to drip and flood irrigated treatments under varying heat stress induced by interannual variation in weather. Field experiments were conducted for four consecutive crop seasons [2021-22 (season 1), 2022-23 (season 2), 2023-24 (season 3), and 2024-25 (season 4)] for winter wheat. Five irrigation treatments were employed: (i) 25% MAD (maximum allowable deficit, i.e. irrigation at 25% soil moisture depletion of total available water) with drip irrigation, (ii) 50% MAD with drip irrigation, (iii) 50% MAD with flood irrigation, (iv) farmers' field replication, and (v) rainfed treatment. Among the four seasons, the temperature and rainfall conditions varied significantly. Grain yield was analyzed using heat stress indices derived from air temperature (accumulated heat stress days, heat stress intensity & heat degree days) and observed yield (heat vulnerability index, stress tolerance index & yield stability index) to identify heat-resilient treatments that optimize water use without reducing GY. For all seasons, GY and WP values were highest for 50% MAD drip irrigation, followed by 25% MAD drip irrigation, 50% MAD flood irrigation, and farmers' field replication. In season 1, a heatwave substantially reduced GY in farmers' field replication, while soil moisture-based irrigated treatments showed greater resilience. In season 2, rainfall events during the grain-filling stage, in the absence of heat stress, led to the highest GY and WP in a specific treatment. In season 3, post-heading heat stress reduced grain yield across all treatments compared to season 2. In season 4, a hailstorm at the onset of grain-filling stage reduced yields across all irrigation treatments relative to seasons 2 and 3. Analysis of heat stress indices showed that the conventional irrigation method is more vulnerable to heat stress during critical growth stages, reducing GY. Soil moisture-based irrigation scheduling helps minimize the adverse impact of heat stress on wheat yield.