Building the lighter density industrial zones will make the farms.
Agricultural is different than Industrial even though they're clumped together. The best way to start out is farms in one corner and then build a lot of farms until people move in and populate and then replace them with medium industrial and invest in water treatment plants to clean up the damage.
Of course realistically your environment needs to be shit for awhile in the beginning. There really is no way around farms and the dirty industries. Just keep an eye on it and keep experimenting with different zones until they take hold.
Also scatter parks through out your city. they're very cheap but add a lot to air quality (which makes rich people want to be there).
