Potassium fertilization and defoliation intensity effects on forage characteristics of “BRS Zuri” guineagrass

The objective of this study was to evaluate the effects of different potassium (K) fertilization levels and defoliation intensities on performance of “BRS Zuri” guineagrass Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L Jacobs (syn. Panicum maximum Jacq.). Treatments were the factorial arrangement of three K fertilization levels: 0 (control), 40, 80 kg K₂O/ha/harvest) and two defoliation intensities (10- and 20-cm stubble heights), distributed in a completely randomized design with five replications. The experiment was conducted in Araguaina, TO, Brazil, from October to January, 2020–2021 and 2021–2022. Plots were harvested four times per year with 21-day regrowth interval. The 40 and 80 kg K₂O/ha/harvest fertilization levels had greater HA than the control (5490 vs. 3,440 kg DM/ha, respectively). There was a K fertilization level × stubble height interaction on tiller population. There was greater tiller population at 20- than 10-cm stubble height at 40 kg K₂O/ha/harvest; however, no effect of stubble height was detected at 0 and 80 kg K₂O/ha/harvest. Plots fertilized with 80 kg K₂O/ha/harvest had greater tiller population than 40 kg K₂O/ha/harvest, which was greater than control. Forage harvested at 10 cm had greater crude protein (CP) than 20-cm stubble height (mean = 11.4% vs. 10.8%). Tissue K concentration increased from control to 40 kg K₂O/ha/harvest, but there was no difference between 40 and 80 kg K₂O/ha/harvest (mean = 1.1% vs. 3.5%). The combination of 40 kg K₂O/ha/harvest and 20-cm stubble height may be a desirable management strategy to promote Zuri guineagrass productivity in tropical regions.