Effect of competition on legume persistence

Alfalfa and red clover are the most competitive legumes while birdsfoot trefoil is among the least competitive. Legumes differ in competitiveness. Important features include seedling vigor, growth habit, and rooting characteristics. Rapid regrowth following defoliation also provides a competitive advantage for species such as alfalfa. Defoliation interacts with growth habit in modifying competitiveness. Less frequent defoliation allows grasses to shade legumes, which favors upright legumes such as alfalfa. In most instances, competition occurs between legumes and non-legumes, particularly with grasses, although legume-legume competition may also occur. Most legumes have prominent taproots which allow them to utilize soil water at a greater depth than grasses. Legume competition with non-legumes first occurs during establishment. Enhancement of traits affecting competitiveness through breeding would increase legume persistence. Legume species and varieties vary in their potential to fix N₂, but it is unknown whether legume differences in N₂ fixation provide any competitive advantage since legumes also freely utilize soil N.