As demonstrated in this video, moldy hay does just as good a job as the chemical fertilizers that you pay for. The only problem with this organic method of lawn care is that some too-cool-for-your-lawn neighbours may turn their noses up at your lawn while the moldy hay is present, but who cares about them.
Why do you want to avoid fertilizers? Besides the danger that chemicals can pose to your family and pets, phosphate runoff is a big concern for the environment, particularly if your property is anywhere near a waterway. Too much fertilizer can also ruin plant biodiversity, which can have consequences for local animal life.