22 gallons a minute isn't much in terms of irrigation.  Run for 24 hours straight it only gives you 1.16 acre inch of water.  So if you ran it 24/7 it would take 10 days to give you entire pasture one shot of water.  Ran 24/7 for a month you would be getting a little over 3 inches per acre.  I don't know what the irrigation requirement is for grass in your area.  I would advise you  to talk to NRCS or a local irrigation company and ask about the irrigation requirement for grass in your area.