Defoliation management affects biomass flow and gas exchange in Megathyrsus maximus BRS Tamani grass managed under cutting

The objective was to evaluate the effects of defoliation management in biomass flow and gas exchange in Tamani grass pasture managed under cutting. A randomized complete block design in a 2 x 3 factorial arrangement was adopted, with two defoliation frequencies (DF; 85 and 95% interception of photosynthetically active radiation) and three defoliation intensities (DI; 0.8, 1.3, and 1.8 of residual leaf area index), with four replications. The study was conducted in 2019. Leaf and stem elongation rates, leaf temperature, photosynthesis/stomatal conductance ratio, photosynthesis/ transpiration ratio, and relative chlorophyll index were not affected by defoliation strategies or their interactions. Leaf senescence rate was not influenced by DF, but there was an effect on the lowest DI with an average value of 1.21 cm tiller-1 day-1. The total number of leaves, phyllochron, and tiller population density showed interaction between DF and DI. Defoliation frequency influenced the number of new live leaves per tiller (1.75 and 2.23 leaves tiller-1 for DF of 85% and 95%, respectively). Forage accumulation rate was not affected by the defoliation strategies, with values ranging from 247.82 kg DM ha-1 to 334.97 kg DM ha-1. The variables leaf photosynthesis rate, leaf transpiration rate, carbon dioxide concentration in the leaf, and stomatal conductance differed only between defoliation frequencies. Under the soil and climate conditions of the present study, Tamani grass should be managed with a defoliation frequency of 85% interception of photosynthetically active radiation and a residual leaf area index of 0.8.