Internal efficiency of nitrogen by Amaranthus cruentus under the influence of urea and biochar on semi-arid Alfisols of Northern Nigeri

The study evaluated the dry matter yield (DMY) and internal efficiency of nitrogen (IEN) in Amaranthus cruentus under the influence of urea and biochar amendments in the semi-arid Alfisols of Northern Nigeria. A screen-house factorial experiment was conducted using a completely randomized design, with treatments consisting of different combinations of urea (0 (U0), 32.5 (U1), 65 (U2) kg N ha⁻¹) and biochar (0 (B0), 15 (B1), 30 (B2) t.ha⁻¹).Results showed that the combined application of biochar and urea significantly influenced plant growth and nitrogen use efficiency. The highest DMY (2.16 ± 0.020 g) and IEN (2.06 ± 0.169) were observed in the treatment with 30 t.ha⁻¹ biochar and 32.5 kg N ha⁻¹ urea (B2U1), while the highest nitrogen uptake (3.38 ± 0.773 mg.pot-1) was recorded under sole urea application (B0U2).Biochar-enhanced treatments (B1, B2) generally improved DMY and IEN compared to the biochar-free treatment (B0), suggesting synergistic effects between biochar and moderate urea levels. Biochar application reduced nitrogen leaching losses, thereby increasing nitrogen availability for plant uptake.These findings demonstrate that integrating urea with biochar can optimize nitrogen utilization in Amaranthus cruentus production in semi-arid Alfisols, promoting sustainable nutrient management and improved crop productivity.