This gives me an idea. We have a very large compost pile from mucking out various horse stalls and pens. It's mainly composed of urine-soaked woodchips and mostly broken-down horse manure. There's also some dirt in there as well. As an experiment this summer, I tried growing potatoes and carrots in it. Potatoes did extremely well, the carrots not so much (but I attribute that to poor watering).

It would be interesting to monitor the temperature to see how active it still is, since I can tell that it's not completely broken down yet. I actually have an ESP8266-based temperature sensor around here that I was using to track ambient temp for another fermentation project.

Now I'm thinking of encapsulating its thermistor and putting the 8266 in an IP67 enclosure along with a solar cell and just planting the whole lot on top of the compost pile. It already serves a web page on a .local domain so there would be minimal work required on my part.

I might actually get to that this weekend!

The soil might have actually been too rich for carrots. In my experience with too much nitrogen grow great tops but the root doesn't form properly.

It's the urine. Try sun bleaching it by spreading out the piles to get rid of the ammonia.

It's a hot manure. Break the rules, gardening gets a lot wrong or is to finicky but for a starting idea -

"Hot manures are high in nitrogen compounds, which decompose quickly in the compost pile and generate a lot of heat in the process. In fact, traditional hothouses harnessed the energy of rotting manure to grow seedlings and cuttings during winter. Hot manures include chicken, duck, and horse.

Cold manures are low in nutrients and release less heat as they break down, posing less risk of burning your plants. Examples are cow, goat, and sheep – ruminant animals that regurgitate and chew cud, extracting most of the nitrogen from their plant-based diet before it comes out the other end. Llama and alpaca aren’t ruminants, but their manure is low enough in nutrients to be considered cold."