Optimizing Recoverable Biomass in BRS Capiaçu: Nitrogen‐Driven Structural Modulation and Consequences for Silage Conservation

This study evaluated the effects of graded nitrogen fertilization on the morpho‐agronomic traits, nutritional composition, and silage fermentation of Cenchrus purpureus cv. BRS Capiaçu. Two experiments were conducted. In Experiment 1, a randomized complete block design with four nitrogen rates (0, 50, 100, and 150 kg N ha −1 ) was used to assess biomass yield, structural characteristics, regrowth, and nutritive value. In Experiment 2, silages produced from these treatments were evaluated for fermentation losses, dry matter recovery (DMR), aerobic stability, and nutritional quality. In Experiment 1, nitrogen fertilization promoted quadratic responses in fresh ( p = 0.045) and dry matter yield ( p = 0.039), with estimated maxima at 79.45 and 89.15 kg N ha −1 , respectively. Structural traits, including plant height ( p = 0.041), stem diameter ( p = 0.038), and tiller number ( p < 0.0001), as well as in vitro digestibility ( p = 0.004), also showed quadratic patterns, indicating optimized development at intermediate nitrogen levels. Crude protein increased linearly ( p = 0.002), whereas fiber fractions and nonfiber carbohydrates exhibited nonlinear responses, suggesting shifts in carbon–nitrogen allocation. In Experiment 2, gas losses ( p = 0.002) and silage pH ( p < 0.0001) showed quadratic responses to nitrogen supply, while effluent losses decreased ( p = 0.021) and DMR increased ( p = 0.006) linearly. Fiber fractions declined ( p < 0.0001), whereas total digestible nutrients, net energy for lactation, and in vitro digestibility increased with nitrogen fertilization ( p < 0.0001). Multivariate analysis explained 80.2% of total variation and confirmed the association between plant structural traits at harvest and silage fermentation efficiency. Overall, nitrogen fertilization modulated plant growth, composition, and conservation dynamics, with predominantly quadratic responses indicating diminishing returns at higher rates. Nitrogen application between 80 and 100 kg N ha −1 is recommended to optimize biomass production, nutritive value, and silage preservation.