Optimum nitrogen fertilization rate and nitrogen use efficiency forBrachiariahybrid andMegathyrsus maximusvaries with stage of regrowth

Abstract

AbstractBackgroundTraditionally, 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 ofBrachiariahybrid andMegathyrus maximusat 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−1and harvested after 4‐, 8‐, and 12‐week regrowth.ResultsCrude protein (CP) had a linear response to increasing N fertilization at all stages of regrowth. Herbage yield ofM. maximuswas optimized with 57.1–63.0 kg N ha−1, while herbage yield in 4‐weeks regrowthBrachiariahybrid 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−1in 4‐weeks regrowthBrachiariahybrid and 8‐week regrowthM. 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 regrowthBrachiariahybrid.ConclusionIt was concluded that the herbage yield and nutritive value of 4‐week regrowthBrachiariahybrid and 8‐week regrowthM. maximusare 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.