This study evaluated the interactive effects of low rates (0, 25, 50 and 75 kg N ha⁻¹) of nitrogen (N) fertilizer application and stage of maturity on total N, N fractions and in vitro ruminal N degradability in Brachiaria hybrid, Megathyrsus maximus and Paspalum atratum. The grasses were harvested at 4, 8 and 12 weeks regrowth, except for P. atratum that was harvested at 6 and 12 weeks. There was a significant N fertilizer rate × stage of maturity interaction (p < 0.001) on total N, buffer soluble N (BSN), buffer insoluble N (BISN), acid detergent insoluble N (ADIN) and in vitro ruminal N degradability (ND) in all grass species. Total N, BISN and in vitro ruminal N degradability increased linearly with N fertilizer rate up to 50 kg ha⁻¹ in Brachiaria hybrid and M. maximus and were highest in grasses harvested at 4 weeks maturity. Nitrogen fertilization rate was positively correlated with total N, BISN (r = 0.70 to 0.97) and ND (r = 0.60 to 0.98) in Brachiaria hybrid and M. maximus forage. We concluded that N fertilisation rate of 50 kg ha⁻¹ per application interval is adequate to improve N, N fractions and N degradability of tropical grass forage.

本研究评估了低比例（0、25、50 和 75 kg N ha ^-1）施氮 (N) 肥料和成熟阶段对Brachiaria杂交种中总 N、N 分数和体外瘤胃 N 降解性的交互影响， Megathyrsus maximus和雀稗。草在再生 4、8 和 12 周时收获，除了在 6 和 12 周收获的P. atratum。总氮、缓冲可溶性氮 (BSN)、缓冲不溶性氮 (BISN)、酸性洗涤剂不溶性氮 (ADIN) 和体外存在显着的氮肥施用量 × 成熟阶段相互作用 ( p < 0.001)所有草种的瘤胃氮降解能力（ND）。在Brachiaria hybrid 和M. maximus中，总 N、BISN 和体外瘤胃 N 降解率随着 N 施肥量线性增加至 50 kg ha ^-1 ，并且在成熟 4 周时收获的草中最高。氮肥施肥率与杂种臂章草和大头鱼草的总氮、BISN（r = 0.70~0.97）和ND（r = 0.60~0.98）呈正相关。^{我们得出结论，每次施用间隔 50 kg ha -1}的 N 施肥率足以改善热带草料的 N、N 分数和 N 降解性。