We're hopeful it's powerful, anyway. Things are a wee bit chilly in the hoophouse these days since winter started really moving in, and a neighbor suggested manure for a bit of a heater. The relatively fresh and therefore "hot" manure will give off heat as it decomposes. It will nourish the soil (depleted by our lovely tomatoes and eggplants this summer) at the same time it helps keep our swiss chard, broccoli, kale, and parsley cozy during these long winter nights.
Since this is an experiment, I mixed some in with the soil and some I left only lightly mixed in to the soil. Some we plopped in a corner. And since it's horse manure there's plenty of straw still...well, visible...so that may help with composting/decomposition. Horse manure is not the ideal choice for your garden it should be said. Word has it that since many things (i.e. seeds and grains) simply make their way through the horse and out again that you end up with lots of extra weeds. I do battle some weeds I have seen in the horses pasture at our friends house, so I suspect there is a grain of truth in this.
A book I'm reading at the moment talks about how fresh manure gives off amonia as it decomposes, but my thought is that the hoophouse is fairly well ventilated by nature of its construction it shouldn't really be a problem. We use this practice for our chickens to help them stay warm through the cold weather. We just add a fresh layer of litter periodically to keep things fresh for the girls, and the heat given off by the composting process of their droppings and the bedding keeps them snuggly. And since the door is open all day while they roam there is no risk of anyone getting asphyxiated.
We'll see how things fare. When I went in today to get some greens and check on the plants I did notice that things looked like they were suffering a bit from the cold. Hopefully, this helps until we get the cold frame built.