Influence of plant population, NPK fertilizer rates and types on growth, chlorophyl content and tuber weight of Kpamyo Yam minitubers in Abuja, Nigeria

Abstract

Low soil fertility and inappropriate fertilizer management remain major constraints to seed yam production in the Nigerian savanna. This study evaluated the influence of NPK fertilizer types and rates on growth attributes, chlorophyll content, and tuber yield of Kpamyo yam (Dioscorea rotundata L.) minitubers. Field experiments were conducted during the 2023 and 2024 cropping seasons at the IITA research farm, Kubwa, Abuja, using a split–split plot design with three replications. Treatments consisted of three planting populations (266,000, 133,000 and 88,000 plant ha-1), three fertilizer types (NPK 15:15:15, 20:10:10, and 27:13:13), and four fertilizer rates (0, 200, 400, and 600 kgha⁻¹). Growth parameters, chlorophyll content (SPAD), and yield attributes were measured and subjected to analysis of variance. Results showed that fertilizer types and rates significantly (p<0.05) affected plant height, leaf area index, chlorophyll content, tuber yield, sett multiplication ratio and harvest index. NPK 27:13:13 promoted the most vigorous vegetative growth but produced comparatively lower tuber yield and harvest index, in contrast, NPK 15:15:15 consistently resulted in higher chlorophyll content and superior yield performance. Tuber yield increased with fertilizer rate up to 400 kg ha-1 but declined at 600 kg ha-1. Plant population density significantly influenced tuber size, with higher densities reducing mean tuber weight due to increased competition. The application of NPK 15:15:15 at 400 kg ha-1 provides the optimum nutrient combination for maximizing physiological efficiency and tuber yield of Kpamyo yam minitubers under Southern Guinea Savanna conditions, offering a practical strategy for improving seed yam production in Nigeria.