Sustainable effects of nitrogen reduction combined with biochar on enhancing maize productivity and nitrogen utilization

Long-term chemical fertilizer use poses sustainability challenges for achieving optimal crop yields and may even diminish yields and fertilizer use efficiency. Sustainable and environmentally friendly agricultural practices must address these challenges by reducing fertilizer application. Biochar emerges as a promising solution, with significant potential for enhancing soil fertility and crop yields. However, its efficacy in sustaining or increasing crop yields under reduced nitrogen (N) fertilizer application remains unclear. This three-year summer maize field study (2019–2021) aimed to elucidate the impact of biochar application on crop productivity, soil characteristics, and economic benefits under varying N fertilizer regimes. Four biochar application rates (0, 8, 16, and 24 t ha⁻¹) were evaluated alongside three N fertilizer rates: conventional N application (200 kg N ha⁻¹), 20 % reduction in N application (160 kg N ha⁻¹), and 40 % reduction in N application (120 kg N ha⁻¹). Biochar was incorporated once at the start of the experiment, while N fertilizer was applied annually. The comprehensive analysis of the three-year data revealed consistent improvements in maize growth, N uptake, grain yield, and economic returns with biochar, even amidst N fertilizer reductions. While the initial year displayed indistinct biochar effects on maize productivity, its impact was more pronounced in the second year than third year. Path analysis underscored the pivotal role of increased soil organic carbon (SOC), total N content, and cation exchange capacity in enhancing maize yield and its components. Moreover, combinations of 40 % N fertilizer reduction with 16 t ha^–1 biochar maintained higher maize yields in 2020 and 2021, suggesting the suitability of biochar rates for sustained efficacy over 2–3 years. On average, maize grain yields increased by 8.5–18.4 % with biochar addition from 2019 to 2021, while economic benefits increased by 15.1–18.4 % in 2020 and 2021. These findings highlight the enduring effects of biochar on crop productivity over at least three years, indicating its potential to consistently enhance maize yield and net income while promoting sustainable agricultural practices.