Nitrogen Fertilization Contributes to the Flexible Use of Defoliation Severity in the Management of Aruana Guinea Grass

Defoliation severity and nitrogen fertilization trigger physiological and morphological responses in individual plants. The objective of this study was to evaluate the capacity of Aruana guinea grass to respond to severe defoliation and to determine whether nitrogen fertilization interferes with the biomass partitioning and nitrogen concentration of this plant. Cylinders containing plant + soil material were collected on Aruana guinea grass pasture and the experiment was conducted in a greenhouse between November 2012 and March 2013. The treatments consisted of four nitrogen rates (50, 100, 150 and 200 mg dm-3) and two defoliation severities (10 and 15 cm heights) in a randomized complete block design, with four replications in a 4 x 2 factorial arrangement. More severe defoliation (10 cm) compared to lenient defoliation (15 cm) seems to induce compensatory growth, since greater biomass accumulation in leaves, a larger leaf area and a higher leaf/stem ratio were observed at the highest nitrogen rate evaluated (200 mg dm-3). Aruana guinea grass can be managed using more severe defoliation (10 cm) as long as sufficient nitrogen is supplied to compensate for the greater removal of tissues through morphological and physiological alterations.