does anyone know if chicken manure is good fertilizer and how much to use on a 20 by 15 garden.

Yes you can use chicken manure...It is very high in nitrogen, The best time to use it is after your garden is finished, so it will have all winter to break down and not burn your plants. How much to use, would depend upon what kind of soil you have and what kind of things you are going to be growing. But if it was me using it, I would spread about a 4 inch layer over the soil and then till it in real good. Someone else I am sure will be along with a better answer soon.

Chicken manure is wonderful fertilizer since it contains Nitrogen, Phosphorus and Potassium; however, I wouldn't put any fresh chicken manure in your garden because it's too hot when it's raw and it can damage the roots and kill your plants. You can compost it and turn it into "black gold" for your garden and your plants will love you for it. I would put the chicken manure into your compost pile or bin and let it cure for approximately 3 or 4 months before you use it. When it's ready it will be dark, crumbly and kind of earthy smelling.