Nitrogen‐Driven Changes in Canopy Structure Enhance Productivity and Efficiency of Guineagrass ( Megathyrsus maximus ) cv.

ABSTRACT

Understanding the responses of forage cultivars to nitrogen (N) fertilization is essential for developing efficient strategies for the sustainable intensification of pasture‐based livestock systems. This study aimed to evaluate the effects of increasing N doses on forage production, canopy structure, nutritive value, and agronomic efficiency of Megathyrsus maximus cv. BRS Quênia pastures under intermittent stocking. The experiment was conducted over 2 years using a randomized complete block design with four N doses (75, 150, 225, and 300 kg N ha ⁻¹  year ⁻¹ ) and four replications. The following variables were assessed: grazing interval, canopy height, tiller population density (TPD), forage mass (FM) and accumulation (FA), morphological composition, nutritive value, and agronomic efficiency index (AEI). Increasing N doses reduced the grazing interval from 60 to 25 days and increased the FAR from 71 to 169 kg DM ha ⁻¹  day ⁻¹ . Forage production (FP) increased linearly, reaching 21.060 kg ha ⁻¹  year ⁻¹ of dry matter at the highest N doses in Year 2, representing an increase of up to 48.5% compared to Year 1. The AEI was higher in the second year, with a maximum value of 486% observed at 300 kg N ha ⁻¹ . Higher N doses increased TPD (565 tillers m ⁻² ), with greater leaf proportion (49%) and lower dead material (16%). In contrast, the lowest N dose resulted in reductions of up to 40% in TPD and 48% in FP in Year 2. Nutritive value was also influenced by N doses, with increases in crude protein (up to 14.7%) and digestibility (up to 59.6%). The lowest N dose (75 kg N ha ⁻¹  year ⁻¹ ) compromised productivity in Year 2, indicating that at least 150 kg N ha ⁻¹  year ⁻¹ is required to maintain pasture stability. Above 225 kg N ha ⁻¹  year ⁻¹ , agronomic benefits were marginal relative to economic costs and environmental risks. Therefore, the range of 150–225 kg N ha ⁻¹  year ⁻¹ represents the optimal balance between productive intensification, economic viability, and environmental sustainability under climatic variability.