Disabling force field effect in particle system?

Hey guys, I’m building a space scene where I have two particle systems (1. the asteroid field, 2. a particle beam from the sun in the center). For the beam, I’ve enabled force field physics so it can follow a nurbs path, BUT now my asteroid field is also being effected by the force field but I don’t want it to. Anyone know how to deactivate the force field effect in a particle system?