Many organic soils contain things like poultry wastes- good fertilizing material for plants, smelly and potentially germ-bearing for tortoises.
My experience with potting soils is that they are muddy and messy in the high-humidity, 'always on the move' Red-footed habitat.
If you want a soil-based substrate, consider mixing it with sand and things like bark mulch to make a soil-like material with less actual soil. Then, add some earthworms and isopods (pill bugs), and a scoop of garden soil to make a bioactive substrate. (https://sites.google.com/site/tortoiselibrary/the-work-shop/substrates-1)