Impact of sowing density and harvesting management on pattern of hard seed breakdown in alfalfa [Medicago scutellata

To evaluate the effects of deferred harvesting, sowing density and harvest intensity on hard seed and breakdown trend of an annual medic (Medicago scutellata var. Robinson), an experiment was conducted in the Research Farm of Agriculture Faculty, Tehran University in Karaj, Iran during the 2005 growing season. The experimental factors were arranged in split-split plots based on a complete randomized block design with four replications. The method of harvesting (continues or deferred), the sowing density (25, 75 and 225 plants/m2) and the harvest intensity (cutting from ground level of 2, 4 and 8 cm) were allotted to the main, split and split-split plots, respectively. The results showed that present hard seedness followed a decreasing trend when sowing density decreased and harvest intensity increased. Present hard seedness was 83.3% in August during harvest of pods which was decreased to 52.7% in March. After harvesting, present hard seedness decreased in all treatments. These results suggest that when low sowing rate and severe defoliation decrease the seed production (data not shown), plants increase hard seed breakdown for fast regeneration and survive in next years which can be noted as a pasture management strategy.