Sounds ike you need lime, but as has been said, you need a soil sample to be sure. If you do need lime, do that first, then when it's had a chance to take effect, apply some fertilizer. The nutrient levels in fertilizer vary depending on what you want it for. Fertiliser intended for hay production causes fast, rich growth. That for grazing is more sow-release in effect. Off-hand I can't remember what the propotions are, but the supplier will explain. If you spread the stuff intended for hay production, your sheep will get a severe dose of the trots! This would happen to a lesser extent even with untreated rich spring grass, but they will be fine. You only need to lime about every 5 years usually, but fertilising can be every year if you want - not compulsory!