You can lay down compost, municipal sludge, or composed manure. Don't use horse manure as it often has a lot of sawdust with it. Even a dairy that beds with sawdust will have much more manure in the mix than a horse operation. If you get it fresh, compost it for a couple of months before using it around the trees. I don't know what kind of area you live in, if you are in close residential quarters, manure is probably not the best option unless it is already composted. You might be able to find a product called sweet peat around you, which is manure mixed with yard waste and composted. You want an organic product that will supply nutrients but at a slow rate so as not to overload the plants. Most commercial products are too heavy on nitrogen and too light on phosphorous, which is the root important nutrient. Manure supplies phosphorous well which is my basis for recommending it. The downside is, you are only going to be able to put this on the surface, and you will lose some nutrient value. Manure and compost do their best work when they are soil incorporated - meaning tilled in.