Tailoring biochar–nitrogen strategies to soil texture: Enhancing wheat yield and moderating downward nitrogen movement in semi-arid agroecosystems

• Biochar–nitrogen interactions exhibited strong soil texture dependency, governing wheat yield responses and patterns of downward nitrogen redistribution under semi-arid condition. • In sandy loam soils, higher biochar rates combined with urea enhanced grain yield but were associated with increased sub-root-zone NO 3 – -N values, indicating greater downward nitrogen mobility beyond the effective rooting zone. • In silty clay loam soils, moderate biochar application (≈40 t ha −1 ) combined with ammonium nitrate provided a balanced agronomic–environmental outcome, improving nitrogen use efficiency while limiting downward nitrogen redistribution. • Grain yield was strongly correlated with dry matter accumulation (r = 0.93 ** ), whereas sub-root-zone NO 3 – -N values showed negative associations with grain yield and protein concentration, highlighting nitrogen use efficiency as a central integrative mechanism. • ASPIM-Wheat and HYDRUS-2D reproduced crop growth dynamics across soil textures but showed systematic bias in simulating downward nitrogen redistribution, particularly across biochar rate gradients. • The results emphasize that soil-specific integration of biochar rate and nitrogen fertilizer source, rather than universal application strategies, is essential for enhancing productivity while moderating environmental risk in semi-arid wheat systems. This multi-year field–modeling study examined the interactive effects of biochar application and nitrogen fertilizer source on wheat productivity and downward nitrogen redistribution, assessed using a sub-root-zone NO 3 – -N indicator (80–100 cm), across three contrasting soil textures (sandy loam, silty clay loam, and silty clay) under semi-arid conditions. Field experiments were conducted over three consecutive growing seasons using a uniform nitrogen rate (60 kg N ha −1 ) supplied as either ammonium nitrate (AN) or urea (NN), combined with three biochar application rates (20, 40, and 80 t ha −1 ) applied once at the beginning of the experiment. Results revealed strong soil texture dependency in both agronomic and nitrogen-redistribution responses. In sandy loam soils, grain yield and biomass showed high responsiveness to biochar–nitrogen co-application, particularly under higher biochar rates combined with urea; however, these gains were accompanied by elevated sub-root-zone NO 3 – -N values, indicating increased downward nitrogen mobility beyond the effective rooting zone. In contrast, silty clay loam and silty clay soils exhibited greater intrinsic buffering capacity, with moderate biochar application (≈40 t ha −1 ) combined with ammonium nitrate providing a more balanced outcome by enhancing nitrogen use efficiency while limiting downward nitrogen redistribution. Statistical analyses confirmed significant main and interaction effects of year, biochar rate, fertilizer source, and soil texture (p < 0.05). Correlation analysis demonstrated a strong positive relationship between grain yield and dry matter (r = 0.93 ** ), alongside negative associations between sub-root-zone NO 3 – -N values, grain yield, and grain protein concentration, highlighting nitrogen use efficiency as a key integrative mechanism linking agronomic performance and nitrogen redistribution. Integrated simulations using APSIM-Wheat and HYDRUS-2D reproduced crop growth dynamics across soil textures but exhibited systematic bias in simulating downward nitrogen redistribution, with overestimation at low biochar rates and underestimation at higher rates. These discrepancies likely reflect structural limitations in representing time-dependent biochar effects, dynamic sorption processes, and microbially mediated nitrogen transformations rather than deficiencies in experimental data. Overall, the findings demonstrate that biochar–nitrogen integration can enhance wheat productivity and moderate downward nitrogen redistribution under semi-arid conditions, provided that biochar rate and fertilizer source are carefully matched to soil texture. Moderate biochar inputs represent a context-specific compromise between agronomic benefits, environmental protection, and practical feasibility in semi-arid wheat systems.