Biochar increased water productivity and grain yield of winter wheat by alleviating post-anthesis drought stress under limited irrigation

Post-anthesis drought is the main limited factor for winter wheat production under limited irrigation in the North China Plain (NCP). Application of biochar has been demonstrated as an effective measure to alleviate water deficit stress. Therefore, a field experiment was conducted at the Xinji Experimental Station, Hebei, China, over the two wheat growing seasons (2023–2024 and 2024–2025) to clarify the combined effects of irrigation and biochar on soil-root-canopy traits. The main plots consisted two limited irrigation regimes, i.e., W1 (75 mm irrigation at the jointing stage) and W2 (75 mm irrigation at the jointing and anthesis stage, respectively); sub-plots included four biochar application rates, i.e., 0, 3, 6, and 9 t ha−1 (B0, B3, B6, and B9). Biochar reduced soil bulk density but significantly increased field water capacity, which increased the root length density and root surface area density in the topsoil layer. During the grain filling stage, biochar (B3 and B6) sustained high SPAD values and relative water content in flag leaves. It also significantly alleviated leaf senescence (as evidenced by higher SOD and lower MDA) and increased photosynthesis rate. Accordingly, starch content in spikes and post-anthesis dry matter accumulation both increased. Additionally, when soil moisture was relatively sufficient (W2 and W1 in rainy 2024), the application of biochar resulted in higher water use. W2B3 showed the most significant yield increase, with a 9.2%-10.5% increase compared to W2B0, while W1B6 showed the most significant yield increase, with a 5.4%-8.7% increase compared with W1B0. Averaged across two seasons, biochar application significantly enhanced water productivity by 2.0%-4.5%. We concluded that moderate biochar could effectively optimize soil and root properties, mitigate leaf senescence and increase grain yield of winter wheat under limited irrigation in the NCP.