Productivity of low-yielding forage stands can be improved through interseeding. Interseeding a legume into a grass stand, for example, can increase yields, improve forage quality, and reduce the need for nitrogen fertilizer. Introducing a productive grass into a thin, unproductive grass stand can also help improve yields.
Depending on moisture, a late-summer seeding in mid-August can yield good results. Closely graze the pasture to reduce competition beforehand, as seeding into a more open stand will increase your chances of succes.
For more information, check out this factsheet on improving pasture and hayfields by no-till interseeding!