I have always heard that you can pour used cooking oil into the ground and that this is "food for the earth worms." Is this true? Does it make a difference if it is vegetable oil or animal fat?
I never heard that. I think the fire ants would love it and the animal fat too.
Well, it's food for something, but probably not earthworms in a direct sense. Most of it will probably be metabolized by bacteria and fungi if they can scrounge up enough N to do something useful with it. Earthworms may eventually benefit from consuming the bacteria.
Veg oil is high in energy, high in carbon, with no nitrogen, and harder to break bonds than, say, sugar, which is also high energy, high carbon, no N.
I cook with olive oil or canola or just "vegetable oil" and I either pour it over my fence into a strip of brush I keep behind my house, or into the compost, no problems with it.
Cooking oils can cause major problems with soil and compost, depending on the amount poured on any one place at any one time. Plants can die and nothing may grow there for some time, depending on the Soil Food Web that is there. Eventually the Soil Food Web will digest that oil, just as they will digest about any other bio hazard.
The compost pile is not really a good place either for the same reasons, although small quantites might not be too harmful for too long.
We have never used cooking oil in large enough quantities to have any that needed dumping, a tablespoon at one time is about all, so I am not sure just how to dispose of a lot other then to put it in a container and put tht in your trash. Fats, which cooking oils are, are not food for earthworms.
Small amounts of fats, scattered, can be handled by an ordinary working compost pile, although the odor may attract rodents, opossums, raccoons, dogs and cats. Larger amounts, no.
Pouring it onto the soil, NO.
If you do a lot of deep-fat frying, or are talking about restaurant-volume waste, collect it in sealed containers and offer it for free on your local Craigslist for those people who make their own bio-diesel.
I don't do a lot of deep-fat frying, but I do cook quite a bit and make my own homemade stocks that I use to make soups and stews that I give to friends and relatives. It is amazing to me how much fat is rendered from beef marrow bones and chickens. I also will slow cook a fresh ham and that produces quite a bit of lard. Cooking bacon produces a lot of fat, too.
I save the rendered fat in jars and freeze them and use small amounts for other dishes from time to time. However, it ends up accumulating since I don't use much at all. Now I would like to dispose of it.
I don't have a composter since I live in a townhouse and the HOA would not allow something like that. I was hoping to do something with it other than just toss it in the trash. I don't have all that much of it so I am not sure it would be worth anyone's time to come pick it up from me. They would probably use more in gas to come get it than they could produce in bio-diesel.
I read about making soap from the beef tallow, but that involves using lye, and I don't think I want to try something like that. Would it help the soil if I dribbled small amounts from time to time on my yard? I don't have to dispose of it all at once or all in the same place. Or is it just not something that helps the soil?
When I was a kid, we had a funnel on the back porch welded to a copper pipe which ran through the porch floor boards and deep into the ground. All of our cooking liquids ended up in the funnel.
Our compost pile was a salvaged U.S. Air Force trash can which my father buried in the ground after removing the bottom of it. The lid was level with the ground. I still have the lid to that garbage can and it has a date on it: 1945. I'd still have the can, too, if my snowplow man hadn't decided to ride waaaay up on my lawn, where he ripped the can out of the ground.
Apparently they don't make trash cans like they used to! No surprise I guess.
yumtomatoes, are you by any chance a person who feeds birds? You could make some dandy 'suet blocks' with all that fat. We get several varieties of birds that just love them.