Effects of Defoliation Intensity, Frequency and Time of Final Defoliation of Seed Yield of Barrel Medic

Swards of barrel medic (Medicago truncatula cv. Parnggio), sown at 20 kg/ha (1990), or 20 kg/ha or 200 kg/ha ( 1991 ), were mown to 3 or 6 cm height at intervals up to flowering, or 10 or 20 days after the start of flowering. In 1990, the swards were heavily grazed in July before imposing the defoliation treatments; in 1991 the swards were mown to 3 cm once in July. The responses to defoliation differed between the 2 years, because of the vigour of the sward at the time of imposing the cutting treatments. In 1990 severe defoliation at flowering or during flowering reduced yields because of reduced pods/m1 and mean seed weight. In 199 I, severe defoliations before flowering generally increased yields because of increased pod set and/or seed size and number of seeds per pod. The results of the 2 experiments show the importance of canopy growth during flowering and the necessity to manage it to maximise light penetration and water use for pod set and seed development.