The area around old plants is also dry and infertile. Old alfalfa plants are efficient in removing essentially all the water and nutrients in the area. It has been suggested that farmers take Apron-treated commercial seed and retreat the seed with a second application of the fungicide before sowing. This load of Apron could injure the seedling and is probably illegal. Even if it works we don't recommend using products off label.
Competition is for light, water, and nutrients.
Even very thin old stands provide stiff competition for light and water as new seedlings attempt to establish. In addition, the old plants emit compounds toxic to the germination and growth of new alfalfa seedlings. This allows the pest pressures and autotoxic compounds in the soil to dissipate completely before new alfalfa seedlings are established. Another benefit is the control of troublesome weeds. If an old stand is moldboard plowed, a new stand can be established in approximately 6-8 weeks.