Effects of regulated deficit irrigation and biochar application on water-saving, emission reduction and yield stability from maize-wheat rotation cropland

In order to investigate the effects of biochar on soil CO₂ emissions, water use efficiency, and yield under regulated deficit irrigation, and to establish a suitable water-biochar management model for maize-wheat rotation farmland in the North China Plain, a field plot experiment was conducted using the summer maize-winter wheat rotation system as the research object during 2021—2022 and 2022—2023. In the summer maize experiment, three irrigation modes were set (WI: conventional irrigation, WJ: deficit irrigation from jointing to anthesis, WA: deficit irrigation from silking to grain filling) and three levels of biochar application (B0: no biochar, B15: biochar applied at 15 t/hm², B30: biochar applied at 30 t/hm²). In the winter wheat experiment, three irrigation modes were set (WI: conventional irrigation, WJ: deficit irrigation from jointing to heading stage, WA: deficit irrigation from flowering to grain-filling stage) and three levels of biochar application (B0: no biochar, B15: 15 t/hm² biochar, B30: 30 t/hm² biochar). A two-factor randomized block design was used, with a total of nine treatments. During the experiments, soil moisture, pH value, organic C and temperature were determined. The CO₂ emission was collected and measured. The crop yield and its comonent was also measured. The water use efficiency was calculated. The results showed that: 1) Biochar can significantly increase soil water content and organic carbon content; the effect of irrigation on soil water content shows significant inter-annual differences. 2) Soil CO₂ emission flux exhibits seasonal dynamics, being high during the summer maize season and low during the winter wheat season, and is significantly affected by soil temperature and moisture, with correlation coefficients of 0.991 and 0.655, respectively. Deficit irrigation can significantly reduce total CO₂ emissions, while biochar application significantly increases total CO₂ emissions. 3) Irrigation and biochar both have significant effects on annual yield, water use efficiency, and CO₂ emission intensity. Due to the temporal effect after biochar application, there are inter-annual differences in the water-biochar interaction. In summary, the WAB30 treatment maintains the highest water use efficiency without significantly reducing yield and achieves the lowest CO₂ emission intensity, and thus the treatment of deficit irrigation from flowering to grain-filling state comined with biobar application of 30 t/hm² was suggested as a suitable irrigation and biochar application mode for the winter wheat and maize rotation areas. This study provides scientific evidence for an appropriate water-biochar management mode for water-saving, yield-stabilizing, and emission-reducing maize-wheat rotation farmland in the North China Plain.