I've heard it said that the soil micro-life killed off by conventional farming as practiced for a century in many countries is still alive in parts of Bulgaria, at least where subsistence farming still goes on. Any ground that's always been worked organically tends to have much higher vitality. The bacteria originally present in living soils enabled the crop plants to take up and present minerals in a liquid state digestible for us, which doesn't happen in chemically treated soils. These bacteria are long gone in the UK and converting back to organic doesn't replace them.
I should think the donkeys &
poultry will have more to do with soil fertility than the septic tanks, but certainly everything is best recycled. Not through the horrible practice of spraying treated sewage on the fields, but using the site of an earth closet to grow a fodder crop for the livestock ensures that it passes through three life forms (bacterial/fungal, plant, and animal) before it comes back to us. Animals bedded on straw produce wonderful material for enriching the soil, and if only the cattle slurry from large dairy farms was sprayed onto straw or bracken and stacked up to rot aerobically instead of stagnating in storage lagoons, all our farms could be much healthier. Mixed farming is sustainable within itself the way arable is not and animal farming alone is not, and I wish I could live to see the day when governments admit that working with nature creates balance and brings success, where working against nature always leads to problems and ill health. That said, some sticks (like black-currant and elder) grow very easily wherever you push them into the soil, as you find out if you use living twigs for pea sticks!