Effects of sequential defoliation on lucerne ( Medicago sativa L.)

The effects of the length of the defoliation period (sequential defoliation) on total matter yield, regrowth, root weight, root total non-structural carbohydrate (TNC) and root protein were measured over five growth cycles of glasshouse-grown lucerne. The treatments were: (1) control, complete defoliation 14 days after 10% flowering; (2) top half of plant cut on day 11 and the rest on day 14; (3) top half of plant cut on day 7 and the rest on day 14; (4) top third of plant cut on day 0, next third on day 7 and the rest on day 14. Sequential defoliation treatments reduced dry matter yields, by slowing down shoot regrowth and delaying phenologic development. The root weight of lucerne decreased as soon as tops were cut, and this loss was most evident with sequential defoliation treatments. Over the five growth cycles examined, treatment 4 plants maintained root size but had a significant decline in the percentage of TNC in roots. Those of treatments 1, 2 and 3 gained in root size and maintained the percentage of TNC in roots. Results support the management principle of keeping the grazing period of lucerne to a minimum by providing adequate subdivision of lucerne swards and by adjusting stocking rates. Levels of TNC over time might provide a useful tool for field studies in the development of management strategies for lucerne.