Effects of biochar and poultry manure on soil properties, growth and yield of yam in degraded tropical Alfisol in Southwestern Nigeria (2023-2024)

Soil degradation poses a major challenge to sustainable yam (Dioscorea rotundata) production in tropical regions due to continuous cultivation and declining soil fertility. This study presents the first field-based two-year factorial evaluation of cocoa pod husk biochar (CPHB) combined with poultry manure (PM) on yam performance in a degraded tropical Alfisol at Owo, southwestern Nigeria. The experiment was arranged in a factorial design with three CPHB rates (0, 15.0, and 30.0 t ha-1) and three PM rates (0, 10.0, and 20.0 t ha-1), replicated three times over two consecutive years (2023 and 2024). Results showed that CPHB and PM, applied singly or in combination, significantly (p < 0.05) improved soil physical and chemical properties compared with the control. The combination of 30 t ha-1 CPHB + 20 t ha-1 PM produced the most favorable soil conditions—lower bulk density, higher porosity and moisture content, and enhanced nutrient status—and significantly increased leaf N, P, K, Ca, and Mg, as well as growth and tuber yield. Averaged over the two years, the highest tuber yield (46.1 t ha-1) was obtained from the combined application of 30 t ha-1 CPHB + 20 t ha-1 PM, representing substantial yield gains over individual or the control. These findings demonstrate the synergistic potential of biochar and poultry manure in improving soil fertility and promoting yam productivity. However, given the high amendment rates, practical adoption will depend on local availability, transport logistics, and labor, and further economic evaluation is recommended to assess economic/on-farm feasibility on degraded tropical Alfisols.