I know when I was really into fly fishing for trout, some of the best areas ran through the farms around where I grew up. Most of the time, if you present yourself as a respectful, responsible person, the people who owned the land would grant you access. I am a catch and release guy (trout included) but I always offered to bring them some if they would like.
A few things:
1. Dont drive on their grass. Specifically ask where you can drive and park.
2. Pick up after yourself. Sure fire way to never gain access again is to leave your junk on the ground after you leave.
3. SAY THANK YOU SIR (MA'AM), whether the answer is "yes" or "no". Just by doing this, I have had a "no" magically turn into, "Well, I suppose you can go ahead and fish.
Politeness goes a long way with property owners (and a lot of other people), show respect and you will likely get it in return.
Wayne