Mitigating heat impacts in maize (Zea mays L.) during the reproductive stage through biochar soil amendment

Heat stress accelerates soil drying and drought effects and changes crop water-utilization patterns, especially in the reproductive growth stage. However, the mitigation of heat impacts through enhancing soil water-holding capacity has received limited attention. Here, we first examined heat impacts on maize grain weight during the reproductive growth stage in a 2-year field experiment (Exp. I). Subsequently, we investigated a possible heat-mitigation mechanism associated with the application of organic materials (biochar [BC] or organic fertilizer [OF]) by analyzing the soil–canopy system in the 3rd year (Exp. II). In Exp. I, average grain weight decreased 25–32% in 2018 compared with 2017, mainly because of high temperatures during the reproductive growth stage. Compared with the control treatment, average grain weight in Exp. II in 2019 improved by 15 % in the BC treatment and 7% in the OF treatment, mainly due to the higher soil water contents in the treated plots (0–20-cm soil layer). The soil water-holding capacity improved by 8% in the BC treatment and 5% in the OF treatment. Meanwhile, soil and crop canopy temperatures decreased markedly in both treatments, leading to significantly improved photosynthetic characteristics. Increasing the soil water-holding capacity as an adaptation to heat stress through effective amendments such as the addition of BC is likely to become progressively more important because heat stress is predicted to be more frequent and severe due to climate change in the future.