Should be fine to use just as you had before.

The thing to remember about compost is that it is partly degraded biological material. What is left behind is the cellulose and lignins that take longer to degrade. That's the fiber. It's still there, but the fibers may be pretty small. As long as there is anything left behind, it's compost, and is a fine soil amendment. But it's true that when completely degraded, it's gone. CO2. Poof. That won't help the soil much. Seriously, biological material left to degrade eventually just disappears.

Except that I hope that I count on the worms that it attracts prior to its evaporation to perpetuate its effects somewhat.

I bet that degraded, fine, compost would make a nice looking upper mulch over something less attractive.

To the extent that the worms are living on the compost, when the compost is gone, they're dead.

Hard to believe that "old" compost is bad. Might have less of a high fertilizer impact, but would still be great additive to soil. Sounds like a good problem to have, too much decomposed compost.

Some of the compost is bone dry (and hard)since it is lying in the neighbourhood of roots from a nearby fig tree.

Will that compost be completely nutrient free and only be of use as a soil amendment?

Most likely moistening a bit will soften it up, it being dry isn't permanent. It will have some nutrients but compost mostly a soil amendment anyway.

With regard to compost disappearing, let me tell you a real story. I have a "compost pit" in my back yard. I dump kitchen compostables in it, and dig the stuff in. I probably put in three or four pounds every week. During the summer, the top of the pile doesn't increase in size. That is, the pile doesn't get higher! In the winter, the pile tends to puff up a little, but in the summer, the top of the pile stays dead flat. Over the years, I've put *hundreds of pounds* of material in that pit, and the pile doesn't increase in size. Yep, the stuff disappears. Magic, eh? So yes, I've seen my compost go "poof" in much less than my lifetime. You can too, but it helps to be in a hot climate.

Now, the degradation activity in that pile is faster than in a regular compost pile, because it's in the ground, and it stays moist. Above-ground compost piles won't degrade anywhere near as fast. Within a week or two the vegetative material I dig in becomes unrecognizable. For above-ground compost piles, everyone can see that they decrease in size with age.

By the way, "bog people" are well preserved because the bog they are found in is highly acidic and almost completely anaerobic. Think pickles. Cold as well. Oxidation won't happen if there is no oxygen around. Not similar to a well maintained compost pile.

Re compost nutrients, compost NPK's out as something like 1-1-1. Not highly nutritious, but then again, we use a lot of it. Now, the caveat is that that NPK is achieved after COMPLETE degradation of the compost. So compost is a weak fertilizer, but it's not a "right now" fertilizer. The nutrients are released very gradually.

Is compost with animal faeces or urine at the outset very different from compost made entirely with vegetable matter?

Would it have a higher nutritional value if protected against excessive wind and rain as it m breaks down?

And is there any benefit to adding ,say chicken manure pellets to the mix?

What about seaweed?

Or are those things best added at the last minute when actually preparing the soil/beds for sowing or planting?

Compost made with animal feces is similar to that made with vegetable matter, but it may be infected with disease, though urine is more likely sterile. Hot composting is the safest way to deal with that. Uncomposted feces are high in nitrogen, and may burn plants. Do not use uncomposted feces on plants. Composting will reduce that ammoniacal content to tolerable levels. Of course, bovine and poultry feces are derived largely from vegetable matter, so compost made with it is just one step removed from vegetable matter compost. Seaweed is high in potassium, which might be good if your soil is deficient in potassium. I believe it is pretty low in nitrogen, so is unlikely to burn plants if you apply it uncomposted.

I'm using horse manure that is maybe 15 years old, possibly older. If some of the manure disappeared over the years it really doesn't matter; because when I backed my truck up to the pile and filled it I got a pickup load of manure.

I've been mixing that manure into raw clay with the the sod left in. I dig in 3 inches and don't add any other fertilizer so what nutrition I'm getting comes from the sod layer and the manure. I get a nice black soil that's nice and loose and everything grows very nicely. As an experiment I've grown corn in the same soil here without any improvement or fertilizer and it grows very very poorly, obviously stunted.

You could mix in grass clippings and other greens if you want to see more organic material.

@John D Zn6a PIT Pa

@John D Zn6a PIT Pa

Do you mean horse manure or stable manure?

That is what I have ,a mixture of hay and faeces and urine.

But separately I just put all the weeds and soil together in another place (covered) and get a very airy concoction in the following spring that I lay more or less directly over old beds and plant or so into.

Really weedy ,that is a pain in the hole.

Dan, I know what you mean about disappearing compost. Over the 20 years we've lived here I estimate that I've built at least 100 large compost piles (at least 5/year). This would include about 4-5 giant sized leaf bags per pile along with the same amount of added grass clippings with added garden & kitchen waste + chicken poop. My garden plots should be 2 feet higher than the surrounding ground level but they are not. Compost just vanishes into the soil like magic, no piling up for sure. Each autumn I'll go around the neighborhood and collect as many leaf bags as I can (usually about 40, free on the curbs). My garden soil looks very fertile but it's not bulking up as would be expected from all of the additional compost added annually.

The vast majority of the weight of kitchen scraps - probably 80% or more - is going to be water. As the scraps break down, the water's released and evaporates or drains away. Not so much in winter - frozen - but otherwise, yes. And of course the volume goes down tremendously as things that had structure lose that structure completely (air escapes). (I can reduce the space branches take up by massive amounts just by chipping them.

And of course compost breaks down and is volatilized or disappears as CO2 - no-one's denying that - but that's only part of it. But one shouldn't confuse the volume/weight going down by enormous amounts with it just 'disappearing'. At least in the timescales gardeners care about.

Compost stuff - it will be much less weight/volume. Once more or less finished, it should be relatively stable. Add more next season anyway.

To add to armoured's comments, compost reduces significantly in volume as it ages but it never fully disappears. What remains after all the digestion and decomposition of organic matter is done is humus, a key component of what we consider soil.

HU-904935760 - The barn I go to has two horses boarded there and nothing else except a cat that comes and goes. The horses are in the lower level and there is no floor so since the urine can soak into the soil they don't provide bedding. So what I'm getting is mostly feces with a little hay, but no straw. They moved to dumping on a new pile over the side of a very steep hillside. So for the past two years I've been working the old pile; except that I took some fresh manure off the new pile for my hot frame late last winter.

I can assure you that old, even very old, manure still works fine.

Regarding worms. My compost attracts worms before and after I add it to my garden beds. My theory is that, despite the degradation of the compost, other nutrients in my soil sustain those worms, and their castings contribute more organic matter to my soil. While I agree that soil appears to eat compost, the quality of my soil has been improved over time by the mere addition of vast amounts of now greatly degraded compost. I do apply compost mulch continually, so I don't know if the worms would die once the compost degrades from my beds.

That's fair. About 20% of the carbon that goes into compost ends up as humus, but the majority of carbon volatilizes promptly with oxidation. I didn't mean to imply that it FULLY disappears, but most of it does. Now, to the extent that water is a primary constituent of kitchen compostables, and it evaporates, yep, poof, it disappears. No confusion there. The point is that the vast majority of the mass of organic compostables volatilizes -- both the carbon and the water.

I should add that even humus continues to oxidize, biodegrade, and volatilize, but does so pretty slowly. Without protection from mineral particles in soil, it is gone in a decade or so. Even coal, if powdered, will be degraded microbially and suffer the same fate. That being said, a crystalline form of carbon, like graphite, will survive.

No disagreement with that summary Dan. Overall my point is that for someone starting with old compost, that has already lost most of original volume and weight, this is low on list of issues.

@annpat - I wouldn't worry about the compost worms, they are pretty well adapted to increase/decrease their numbers depending on the food available, and to leave dormant eggs behind ready to hatch in the ground when conditions are good. And old compost that seems like it has nothing left for them to eat apparently has enough to sustain some for quite a while, in my experience (from worm bins) there's always a few hanging around somewhere. They don't seem to require a lot, particularly if you consider some of the stuff in there wouldn't be edible anyway.

"...is it just as good, say for keeping the soil moist in dry weather?"

You are now asking about a role in the garden - mulch. Material that is composting (which, technically, is any formerly living matter) can be used in this role - to keep soil moisture from evaporating rapidly and to prevent weed seeds from taking root. But, as you note, it degrades over time - which is another way of saying that it turns from raw materials into compost, and eventually into humus where it is just part of the soil. This is, of course, as nature intends and is how fertile soil is created.

It will do the mulching job better when it is closer to raw material - like straw, shredded wood and leaves. As it degrades over the years it becomes less valuable as mulch, but more valuable as a soil additive to improve your garden beds.

Which is why Mother Nature keeps an new layer of dead leaves, twigs, and dying annuals on the top every year, as the layers below slowly degrade and build up the soil.

https://www.quantamagazine.org/a-soil-science-revolution-upends-plans-to-fight-climate-change-20210727/

"...for someone starting with old compost, that has already lost most of original volume and weight, this is low on list of issues."

We're not talking about old compost. We're talking about old compost-ables. Old compostables don't necessarily volatilize. They don't necessarily degrade. If they're in a pile, and don't remain wet, they're just going to sit there. That old dry pile won't have lost much of the original hydrocarbon mass.

And let's be clear. You can say that compost eventually turns into humus. But very little of it actually does. Most of it turns into CO2. If Mother Nature's dead leaves, twigs, and dying annuals didn't do that, the soil surface would be getting higher and higher every year. It doesn't.

But no question that using new or old compost as mulch, which retains soil moisture, or as a soil amendment, which improves soil friability, is its main value.

"But no question that using new or old compost as mulch, which retains soil moisture, or as a soil amendment, which improves soil friability, is its main value."

I agree. Which is why I think discussions of how much volatilizes or goes poof or how much remains after what period of time is basically irrelevant to the question posed.

If the op's pile is a couple years old, go ahead and use it.