Abstract
<title>Abstract</title> <p> Maize ( <italic>Zea mays</italic> L.) production in Cameroon is constrained by progressive soil fertility decline, which limits the productivity of conventional cropping systems. Environmentally friendly organic-based amendments are increasingly sought as alternatives to costly and often poorly adapted mineral fertilization. This study evaluated the effects of Biochar enriched with rabbit urine, applied alone or combined with NPK, on the agronomic performance, physiology and soil microbial activity of maize grown on an acidic clay soil at Bafia, Cameroon. The trial followed a randomized complete block design with three replications and eight treatments: unamended control (T0), NPK 200 kg ha⁻¹ (T1), Biochar 2.5 t ha⁻¹ (T2), rabbit urine 2000 L ha⁻¹ (T3), rabbit urine 2000 L ha⁻¹ + NPK 200 kg ha⁻¹ (T4), Biochar 2.5 t ha⁻¹ + rabbit urine 2000 L ha⁻¹ (T5), Biochar 2.5 t ha⁻¹ + NPK 200 kg ha⁻¹ (T6), and Biochar 2.5 t ha⁻¹ + rabbit urine 2000 L ha⁻¹ + NPK 200 kg ha⁻¹ (T7). Growth variables (leaf number, collar diameter, plant height, and leaf area), physiological variables (soluble sugars, soluble proteins, total phenolics, and total chlorophyll) and soil microbial activity were recorded throughout the study. All amended treatments significantly (P < 0.05) outperformed the unamended control for every variable measured. The combination of rabbit urine with NPK (T4) produced the tallest plants (176.6 cm), the largest collar diameter (27.5 mm) and the highest soil microbial activity (3.45 µg mL⁻¹), while the Biochar + rabbit urine combination (T5) maximized soluble protein content (48.6 µg BSA-eq g⁻¹ FW) and the Biochar + NPK combination (T6) maximized total chlorophyll content (7.02 µg mL⁻¹) while minimizing phenolic accumulation (9.17 µg eq g⁻¹ FW), indicative of reduced metabolic stress. These results indicate that Biochar enriched with rabbit urine, whether or not combined with mineral NPK fertilizer, is a promising, low-cost and environmentally sound option for restoring soil fertility and improving maize productivity in tropical, acidic-soil environments such as those found in Cameroon. </p>