Optimizing Cassava Productivity on Coastal Plain Sands: Effects of Integrated Nutrient Management Using Poultry Manure and Microbial Fertilizer (CHC) under Conventional and Reduced Tillage

Abstract

This study evaluated the effects of integrated nutrient management (INM) and tillage practices on cassava growth, yield, and nutrient accumulation on low-fertility Coastal Plain Sand soils in Etinan, Nigeria. Eight fertilizer treatments, including sole inorganic (NPK 15–15–15), sole organic (poultry manure), microbial fertilizer (CHC 240 L ha⁻¹), and their combinations, were applied under conventional tillage (CT) and reduced tillage (RT). Integrated treatments (NPK 400 kg ha⁻¹ + poultry manure 2.5 t ha⁻¹; NPK + CHC 240 L ha⁻¹) produced the highest tuber yields (32.4–36.7 t ha⁻¹) and nutrient uptake (N, P, K) across both seasons. In contrast, sole NPK resulted in substantially lower yields (16.8–23.6 t ha⁻¹), a performance often worse than the unfertilized control, underscoring the limitations of sole mineral fertilization on sandy, nutrient-poor soils. Organic and microbial fertilizers enhanced soil biological activity and nutrient synchrony, improving nutrient uptake—particularly potassium. Tillage effects were generally non-significant for yield, and importantly, no significant fertilizer × tillage interaction was observed for most parameters, indicating that fertilizer type rather than soil disturbance determined cassava performance. Overall, INM—especially NPK combined with poultry manure or microbial fertilizer—proved the most effective strategy for improving cassava productivity and nutrient accumulation on fragile sandy soils.