Interactive Effects of Nitrogen Fertilization and Plant Spacing on Micro-nutrient Uptake in Hybrid Napier Grass (Pennisetum purpureum)

Abstract

Optimizing agronomic management practices is critical for improving the nutritional quality of forage crops for sustainable livestock production. This study evaluated the interactive effects of nitrogen fertilization rate and plant spacing on micro-nutrient uptake in hybrid Napier grass (Pennisetum purpureum). The experiment was conducted at the Teaching and Research Farm of Ladoke Akintola University of Technology (LAUTECH), Ogbomoso, Nigeria, using a 2 × 2 factorial arrangement in a randomized complete block design (RCBD) with three replicates. Treatments consisted of two nitrogen application rates (200 and 400 kg N ha⁻¹, supplied as urea) and two plant spacing (75 and 100 cm). Forage samples were harvested ten weeks after planting and analyzed for zinc (Zn), manganese (Mn), iron (Fe), and copper (Cu) concentrations. Results showed that nitrogen fertilization rate and plant spacing significantly (P < 0.05) influenced micro-nutrient uptake in hybrid Napier grass. Higher nitrogen application (400 kg N ha⁻¹) consistently enhanced Zn, Mn, Fe, and Cu concentrations compared with 200 kg N ha⁻¹. Narrower plant spacing (75 cm) resulted in significantly greater Zn, Fe, and Cu contents, while Mn concentration was not significantly affected by spacing alone. A significant interaction between nitrogen rate and plant spacing was observed, with the combination of 75 cm spacing and 400 kg N ha⁻¹ producing the highest concentrations of all evaluated micro-nutrients. These findings demonstrate that nitrogen fertilization and plant spacing interactively regulate micro-nutrient accumulation in hybrid Napier grass. Optimizing nitrogen input and plant density can therefore improve the micro-nutrient quality of forage, with positive implications for ruminant nutrition and sustainable pasture management.