Objectives This study aimed to investigate the effects of long-term application of different biochar rates on farmland water use efficiency (WUE), nitrogen use efficiency (NUE), and maize yield under different cropping patterns in the dryland area of the Loess Plateau, and to provide a scientific basis for sustainable crop production in mulched farmlands of arid regions.

Methods Based on a long-term field experiment initiated in 2019, two cropping patterns were established: flat planting without mulching (F) and ridge-furrow planting with film mulching (D). Under each pattern, four biochar application rates were applied: 0 (CK), 3000 (L), 6000 (M), and 9000 kg/hm² (H), resulting in eight treatments. Soil water content (0−200 cm), soil nitrogen nutrients (0−60 cm), maize yield, WUE, and NUE were measured from 2022 to 2023.

Results Under both cropping patterns, the high-rate biochar treatment (H) optimized WUE, NUE, and maize yield. Ridge-furrow mulching (D) outperformed flat planting (F) at the same biochar rate. Specifically, compared with the FH, DH treatment increased soil water content, soil water storage, and WUE by an average of 10.19%, 8.96%, and 24.71%, and enhanced soil total N and NUE by 10.38% and 52.17%, respectively. Mulching combined with biochar significantly enhanced dry matter accumulation in maize organs and yield, with synergistic effects escalating at higher biochar rates. Under ridge-furrow mulching, DH increased yield by 2274 and 2258 kg/hm², compared to DCK and FH treatment, respectively.

Conclusions Ridge-furrow mulching combined with biochar application can effectively improve field water and nitrogen use efficiency in maize production. A biochar application rate of 9000 kg/hm² is recommended to achieve high water and nitrogen utilization and maize yield, thereby supporting sustainable agricultural development in arid regions.