TOTAL NONSTRUCTURAL CARBOHYDRATE ACCUMULATION IN ROOTS OF ANNUAL LESPEDEZA

Total nonstructural carbohydrates (TNC) stored in roots are thought to be an important energy source for growth following herbage removal in many forage legumes. This study was conducted to determine if root TN C levels fluctuate during harvest and regrowth cycles of annual lesped eza (Kummerowia spp.). Annual lespedeza management treatments consiste d of harvesting at a 6- or 12-cm stubble height at the end of July and a nonharvested control. Seeding-year 'Nitro' alfalfa (Medicago sativa L.) and 'Norcen' birdsfoot trefoil (Lotus corniculatus L.) were inclu ded for comparison. Alfalfa was harvested four times at early bloom an d birdsfoot trefoil three times at early bloom. Alfalfa exhibited a cy clic pattern of TNC utilization and storage in response to herbage rem oval and regrowth, respectively. Seedling alfalfa accumulated >150 g k g(-1) TNC in the roots by 10 June, and >450 g kg(-1) by first harvest. Seedling birdsfoot trefoil maintained <70 g kg(-1) TNC in the roots t hrough mid-September and did not exhibit as much TNC cycling as did al falfa. Annual lespedeza averaged approximate to 20 g kg(-1) TNC in the roots prior to harvest and maintained <40 g kg(-1) throughout the gro wing season. Harvesting annual lespedeza at 6 cm decreased root TNC le vels for approximate to 5 wk compared with harvesting at 12 cm and the nonharvested controls; however, the total amount of reduction was sma ll. Root TNC Levels decreased by 6.1 g kg(-1) with cutting at 6 cm. As annual lespedeza maintains relatively small amounts of root TNC, leav ing residual leaf area at harvest may be important for regrowth.