Fertilizer is for plants. Feed usually refers to animals. "Plant food" is another name for fertilizer. It's more of a marketing name. When looking at fertilizers, look at the ingredients, use, and label. There are some that will be worse to apply than not, and some that will do wonders for your plants. Consider also that compost and compost teas have a lot of the stuff your plants need and will act as a mild fertilizer (compost is usually rated at about 5% nitrogen). If your land is not already severly deficient in a nutrient, this may be enough for your plants. Raw horse manure is supposed to be 14-4-14 (ie. 14% Nitrogen, 4% Phosphorus, and 14% Potassium). The problem with raw horse manure is salt and flies, but if you get enough rain and spread it or compost it, there's no problem. If your growing a large enough area, it may be good to get your land tested before using any fertilizer. I heard they are like $30. If you dont' like that, you can try reading the plants to see if you can figure out what they are missing. Check out: http://5e.plantphys.net/article.php?ch=3&id=289. In all honesty though, I've never been able to figure out the thing wrong with my plants by this method and I also found out through an accident, that too much potassium will look like iron deficiency.
Anyway, complex, so the best thing is to test the soil and then fertilize (if necessary) based on that and add compost according to what the plants typically need... (or so I think)