Influence of NPK and Gliricidia-based organic fertilizers on soil fertility and performance of millet in Sokoto, Nigeria
Millet (Pennisetum glaucum) is a staple crop in semi-arid Nigeria, but its productivity is constrained by poor soil fertility. While inorganic NPK fertilizers can boost yields, their long-term use may degrade soil health. Organic alternatives like Gliricidia sepium remain underutilized despite their potential to improve soil quality. A field experiment was conducted at the Dryland Teaching and Research Farm, Usmanu Danfodiyo University, Sokoto, during the 2025 cropping season. The treatments comprised: T₁ (NPK 15 g plant⁻¹), T₂ (Gliricidia-based organic fertilizer 100 g plant⁻¹), T₃ (50 g Gliricidia + 7.5 g NPK plant⁻¹), and T₄ (control). The treatments were laid out in a randomized complete block design with four replications. Data were collected on growth parameters, yield components, and post-harvest soil physicochemical properties. Analysis of variance was used to test treatment effects at p<0.05. Fertilizer application significantly (p<0.05) influenced millet growth at later stages. Plants treated with Gliricidia (T₂ and T₃) were significantly taller at 9 and 12 weeks after planting and produced more tillers than the NPK-only and control treatments. Although not statistically significant (p<0.05), the sole Gliricidia treatment (T₂) gave the highest grain yield (1.05 t ha⁻¹), representing a 48% increase over the control (0.71 t ha⁻¹). Post-harvest soil analysis showed that Gliricidia-amended plots had significantly higher pH (6.40) compared to the NPK-only plots (6.31). Available phosphorus and exchangeable potassium were significantly higher in the NPK treatment, while total nitrogen remained unaffected across treatments. Gliricidia-based organic fertilizer effectively enhances millet growth and shows strong potential for improving grain yield while buffering soil pH against acidification. It is recommended as a sustainable nutrient management option for smallholder farmers in the Sudan Savanna of Nigeria.