yeah, I know manure is a decent fuel, about 6,000 BTU per lb uncompressed. If you compress it a bit, you could achieve more BTU (oak, I think is around 8,000 btu per lb)
but, I'm curious about the fertilizer aspect, that sounds interesting.
Some manure might be better than others. Goat, sheep, and
rabbits produce pellets, so that is kinda handy. They also tend to dry faster.