Multiple subscribers list - I set up 2 contacts forms

We have 2 type of customers. 1 with horses and 1 with ATVs. We use the same website to promote our camp. I set up 2 contacts forms, one for each. I then set up 2 subscribers list, 1 for each. I have the opt in button on each form, so I can get them into my mailing list. How do I tell each contact form, which subscriber list to post to?