No one mentioned that alfalfa has a self defeating mechanism. This mechanism is a natural defense to reduce competition that works by preventing germination of seed. The problem arises as the prevention builds annually and reaches a point where even the alfalfa seed struggle to germinate and bald areas begin to appear and the stand thins. Many growers automatically kill it every 5th year and plant a cover crop for 2 seasons before re-establishing. I have kept a stand going for 7 years by regular mowing and fall plantings of cereal rye and turnips which fill in the bald areas, disrupt the chemical mechanism and encourages the alfalfa to spread and compete. I fight the battle because the landowner wants alfalfa, otherwise its too expensive, too needy (spray 3X's year for bugs) and does not do anything a great stand of clover doesnt do better on less acreage for far less money. Oh! and it will disappear in winter leaving bare dirt if you dont plant cereal rye or wheat into it. JMHO