ABSTRACT

Biochar has the potential to effectively improve yield and nitrogen use efficiency (NUE) of upland crops in different soil types. However, it is unclear for rapeseed in purple soil under N reduction. A 2 years field experiment was conducted in southwest China, to evaluate the combined effects of nitrogen (180, 144 and 108 kg ha⁻¹, named N₁₀₀, N₈₀ and N₆₀, respectively) and biochar (0, 10, 20 and 40 t ha⁻¹, named B₀, B₁₀, B₂₀ and B₄₀, respectively) on rapeseed growth, NUE and yield. Compared with B₀, B₁₀ significantly improved growth, NUE and yield, while nitrogen reduction had an opposite effect. The better management practices were N₈₀B₁₀ and N₁₀₀B₁₀, which increased NUE by 10.0% and 10.2%, and grain yield by 16.1% and 21.8%, respectively, compared with N₁₀₀B₀. Path analysis revealed that effective pods and root surface area, root volume had significant and direct path coefficients with variances in seed yield and NUE, respectively. Besides, positive residual effectiveness of biochar was preserved for at least 2 years. This study indicated that B₁₀ could replace 20% nitrogen to promote rapeseed root development and yield formation, thus achieving both high yield and high NUE for at least 2 years in upland purple soil.