how large is your pasture? Is there currently grass in it ? Do you irrigate your pasture or 'dry farm ' it ( as in it only gets watered when it rains)?
Are there other neighbors near you that could give you some advice? You need to make sure you do not have any toxic weeds, you can get weed killers and find the burn off time and if they are safe for pastures. I don't recall what the round up time is, 21 days ? Or 2d4 which is another good killer for pastures , I also use a weed killer that has Diquat in it, for stinging nettles. You can go to home depot lowes tractor supply etc. Your ground may not need nitrogen, so a soil sample is a good idea. Potassium and phospherous is needed for good pasture, as well as a list of other micro nutrients.