Effect of Forage Harvest Frequency on Subsequent Alfalfa Seed Production and Pollen Quality

The most suitable time during the growing season for maximum seed production of alfalfa (Medicago sativa L.) depends on geographic area. This investigation was undertaken to study the influence of four forage harvest treatments on the subsequent seed production and pollen quality characteristics of irrigated alfalfa in Lebanon. In addition, wild alfalfa pollinators were collected and identified. Two seed crops were produced after both one and two forage harvests. After three and four forage harvests, only one seed harvest was produced. The two seed crops following the one and two forage harvest treatments produced mean yields of 1,116 and 1,140 kg/ha, respectively. The first seed crop contributed 83% of the total yield. The seed yield components of number of stems/plant, racemes/stem, pods/raceme, and seeds/pod of the first seed crop were higher than those of the second crop. Hard seed percentages were more than 50% in the second crop where seeds developed between late September and early November, compared to less than 20% in the first crop where seeds developed between late June and end of August. Pollen viability was not significantly influenced by forage cutting treatment. However, pollen tube growth immediately after germination was most vigorous from late May to the end of June. This coincided with the flowering of the first seed crop after one and two forage harvests. Four species of Megachile, nine of Andrena, one of Halictus, one of Anthidium and two of Anthophora were identified as alfalfa pollinators