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PASTURE MANAGEMENT

Effect of Defoliation Management on Water-Soluble Carbohydrate Energy Reserves, Dry Matter Yields, and Herbage Quality of Tall Fescue

Tasmanian Institute of Agricultural Research, Burnie, Tasmania 7320, Australia

^* Corresponding author (Danny.Donaghy{at}utas.edu.au).

There is limited information on the effect of leaf stage based defoliation management on the regrowth of tall fescue (Festuca arundinacea Schreb.). The aim of this study was to investigate the physiological changes in tall fescue during its regrowth cycle up to the five-leaf stage, and the effect of repeated defoliation at the one-leaf, two-leaf, and four-leaf stages on herbage quality, water-soluble carbohydrate (WSC) energy reserves and the rate of subsequent plant regrowth. Crude protein (CP) and metabolizable energy (ME) concentrations decreased with increased leaf regrowth stage, from 27% and 11.3 MJ kg^–1 dry matter (DM) at the one-leaf stage, to 16.1% and 9.2 MJ kg^–1 DM at the five-leaf stage, respectively. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) concentrations increased during the regrowth cycle by 16 and 9%, respectively. Frequent defoliation therefore maximized the CP and ME concentrations and minimized the ADF and NDF concentrations of tall fescue, but limited DM yields during regrowth. Defoliation at the four-leaf stage resulted in 30% higher stubble WSC concentration and 20% higher leaf DM yield than defoliation at the two-leaf stage of regrowth, but compromised herbage quality. The stubble was confirmed as the primary storage organ for WSC reserves, while leaf and root growth were found to have an equally high priority for available energy following defoliation.

Abbreviations: ADF, acid detergent fiber • ANOVA, analysis of variance • CP, crude protein • DM, dry matter • ME, metabolizable energy • NDF, neutral detergent fiber • WSC, water-soluble carbohydrates