Forage accumulation, nutritive value, and grazing efficiency on rotationally stocked ‘Zuri’ guineagrass pastures as affected by pre-graze canopy height and N rate

Grazing management and nitrogen fertilisation may affect forage accumulation (FA), nutritive value, and grazing efficiency (GE) of the highly productive ‘Zuri’ guineagrass [Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L. Jacobs syn. Panicum maximum Jacq.]. The objective of this study was to assess the effects of pre-graze canopy heights [55 and 75 cm (H55 and H75, respectively)] and N fertilisation rates [150 and 300 kg N ha⁻¹ year⁻¹ (N150 and N300, respectively)] on FA, GE, grazing losses (GL), and nutritive value of Zuri under rotational stocking. The stubble height was 50% of the pre-graze canopy height. The total FA was 20% greater under H75 than H55 (22,120 vs. 18,370 kg DM ha⁻¹ year⁻¹), as well as the GL was greater under H75 (85%) than under H55 (79%). Regardless of pre-graze height, the upper stratum of the canopy was composed mostly of leaves contributing to similar crude protein (CP) (142 g kg⁻¹) and in vitro digestible organic matter (IVDOM) (559 g kg⁻¹) concentrations. Greater N rate (N300) increased FA (23,500 vs. 16,980 kg DM ha⁻¹ year⁻¹) and resulted in greater GE (84% vs. 80%) compared to N150. The CP and IVDOM concentrations under N300 (157 and 571 g kg⁻¹, respectively) were greater than under N150 (128 and 547 g kg⁻¹). Zuri guineagrass grazed at H75 has great FA and GE, maintaining a similar forage nutritive value compared to H55.