Azospirillum inoculation of massai grass seeds and nitrogen fertilization: effects on forage development

The demand for sustainable livestock production has intensified interest in biological strategies that enhance forage development while reducing reliance on chemical fertilizers. This study evaluated the effects of seed inoculation with Azospirillum brasilense and four nitrogen (N) fertilization rates (0, 50, 100, and 150 kg N ha⁻¹) on the growth of Massai grass (Megathyrsus maximus cv. Massai) in a greenhouse experiment using a 2 × 4 factorial design. Plant height, tiller number, fresh and dry masses of shoots and roots were measured 60 days after sowing. Nitrogen fertilization significantly increased plant height and tiller number, with the greatest response observed at 100 kg N ha⁻¹ . Inoculation did not improve shoot growth under high N conditions but consistently stimulated root biomass across all N rates. The interaction between inoculation and nitrogen suggests that microbial benefits were more evident at moderate N levels, where A. brasilense may contribute to improved nutrient acquisition and efficient resource allocation. Enhanced root development in inoculated plants may increase soil exploration capacity, potentially improving water and nutrient uptake under field conditions. Combining moderate nitrogen fertilization with A. brasilense inoculation could be an effective strategy to increase forage productivity and nitrogen use efficiency in tropical pasture systems, thereby supporting more sustainable beef production. These findings offer practical insights for integrating microbial inoculants into forage management practices.