Optimum nitrogen fertilization rate and nitrogen use efficiency for Brachiaria hybrid and Megathyrsus maximus varies with stage of regrowth

Background Traditionally, recommended nitrogen (N) fertilization rates that maximize biomass yield and nutritive value in tropical grass forages tend to be fixed and do not consider possible stage of maturity‐induced variations. Therefore, this study investigated biomass yield and nutritive value of Brachiaria hybrid and Megathyrus maximus at different stages of maturity in response to incremental levels of N fertilizer. Both grasses were fertilized with urea at rates equivalent to 0, 25, 50, and 75 kg N ha−1 and harvested after 4‐, 8‐, and 12‐week regrowth. Results Crude protein (CP) had a linear response to increasing N fertilization at all stages of regrowth. Herbage yield of M. maximus was optimized with 57.1–63.0 kg N ha−1, while herbage yield in 4‐weeks regrowth Brachiaria hybrid was optimized with 59.1 kg N ha−1. The combination of herbage yield, 24 h in‐vitro organic matter digestibility, and CP were optimized with 59.1 and 68.2 kg N ha−1 in 4‐weeks regrowth Brachiaria hybrid and 8‐week regrowth M. maximus, respectively. The efficiency of N fertilizer use for herbage and CP yield was highest with 25 and 75 kg N ha−1, respectively except for 8‐weeks regrowth Brachiaria hybrid. Conclusion It was concluded that the herbage yield and nutritive value of 4‐week regrowth Brachiaria hybrid and 8‐week regrowth M. maximus are optimized with 59.1 and 68.2 kg N ha−1, respectively, while all other stages of regrowth were optimized with 75 kg N ha−1.