Soil testing and aeration on a regular annual basis will improve any existing lawn. High usage or heavy clay lawns often require more frequent aeration for best performance. Pastures require high fertility to stimulate maximum growth in the forage material as well as the added weight gains in the livestock. The usage will ultimately determine the amount of fertilizer used. For example when hay is cut fertilizer is applied to spur new growth for the next cutting.
Grazing requires less amounts per year.
Silage, green chop, haying, grazing, and whether companion crops are mixed in with the grass determines your fertilization needs. Contacting your county agent or government USDA office can give you the exact answers to the question of how much do I need to apply. Soils, climate and water all make a difference and there is always the rule of thumb answer but that will not maximize your time or money spent wisely. Perennial is a higher maintenance grass than many others, grows rapidly, and should be kept to keep at 6 inches. Soil testing and adding newer varieties into thinning stands will help develop a new pasture without completely renovating an older one.