Irrigation Pump Question

I am considering purchasing a water reel to irrigate some 5-6 acre pastures that I have. The pastures are hilltops with thin topsoil, and are prone to draught. Each pasture is surrounded by woodland so there is no way  to "go big" with something like a big reel, center pivot, etc. I have a nice size creek running through the property to pump out of.

I always buy at auction, on the cheap, so I am looking at some of the water reels that I can pick up from a turf farm or school district. The kifco B140 appears to be fairly common. Running two of these reels would cover my field and require around 150GPM of water.

 Now, the pump... I would like to get a diesel trailer pump. That would be the easiest to move, and I can find them around for fairly cheap. The problem is all the trailer pumps are BIG capacity. Like 400 GPM and 4" pump outlet.

Will these pumps work if you throttle the engine back to an idle?

I wasn't sure if centrifugal pumps will pump at low RPM. Low RPM pump with a hose split to run two reels would probably get me close to the water I need.

Irrigation Pump Question