You will probably get a lot of answers, but in the nutrition sense, compost isn't worth a bucket of warm spit.

I've waited for years to steal that line. Another way to think on it is compost is more like a catalyst than a chemical undergoing a reaction. It supports other processes than direct nutrition. It allows little creatures to eat and do their excretion thing. It helps mineralize er, uh, minerals so the plant can build big strong muscles. It's at its finest when it's getting down to colloidal sizes, on to (we hope) eventual humus sizes.

Compost as a metaphor for entropy? Heh!

You get far far better NPK nutrition from chemical NPK, but chemical NPK is in no way the only stuff a plant needs. I avoid it. Lots.

So, don't care much what's in your compost. It's not a product that needs a recipe. Make it for its general organic crumbly bits, and realize that it's a crummy fertilizer so you need a lot of it, no matter what it is constructed (destructed?) from.

Almost everything you would put in to compost has nutrients, grass clippings equal Nitrogen around 3 percent, tree leaves too at around 1 percent. All plant materials have many nutrients and are pretty well listed on the 'net.
It is a bit difficult to get a good nutrient level reading on compost because most of then are locked in, not readily soluble like the synthetic fertilizer nutrients are. The nutrients in compost need the activity of the Soil Food Web to release most of those nutrients for other plants to use.

grubby pretty much nailed it :-)) Whatever its mix of ingredients, compost is never going to be a considered a nutrient-rich product - its primary attributes lay in other areas. Everything you add to compost - all those organic materials - will contribute to its nutrient base but the wider the range of organic ingredients, the better the quality of the compost and the wider the range of nutrients it will offer.

'Finished' home compost - yard waste, kitchen scraps, etc. - should assay out at about 1-1.5/.02-.05/.5-1.5.......pretty darn low. Animal based composts (manures) will assay out higher - 2-4/1-3/1-3 depending on source. P and K levels may be excessive in these and soluble salts will be significantly higher than compost sourced primarily from plant materials. Micronutrients will be available from all to some degree or another but not necessarily in a complete array and and in some cases could be present in excessive (toxic) levels.........but this is highly unlikely in a home compost operation and commercial composts are regulated as to the concentrations of these heavy metals.

So as grubby stated, don't consider your compost as a primary fertilizer source. It may very well provide enough of a supplementation to current soil nutrient levels or you may need to add more traditional ferts, synthetic or organic. But all those other benefits of compost are beyond discussion and reason enough for using it liberally.

A bucket of warm spit .... surely an excellent addition to the pile. Anybody tried it?

Nutrients in grass clippings

nutreints in leaves

It's not necessarily the big three that is important, it's the micros.

Lloyd

Many of us that use only organic growing methods find that organic matter, including compost, is all the soil we have needs to stay good and healthy. Soil test have shown that as the amount of organic matter in the soil reaches adequate levels the nutrients also reach optimal, and balanced, levels and plants grow stronger and healthier and are less apt to be bothered by insect pests or plant diseases.
Since the nutrients in compost are not very soluble you do not see them appear in nutrient tests, but they are there.

It does sort of depend.

Nitrogen? Essentially zip. It gets bound into bacterial structure and either out-gasses or washes out when the compost pile ages. Some bound nitrogen will be available, but just adding compost doesn't make a plant grow like using an organic fertilizer. Tentatively, I say that the nitrogen level in compost is 1%. Which is zip on nitrogen.

Phosphorus binds like nobody's business, so whatever was in the original is mostly in the compost. However, phosphorus levels aren't very high in most plant material (there are exceptions). Still, I call compost about 0.5% grand total phosphorus, which isn't bad. Most of that is tightly bound and won't be available any time soon.

Potassium also washes out, but also likes to bind--just not as strongly as some other ions. Again, I call compost 1% potassium, which isn't bad and isn't great.

Calcium, magnesium, iron, boron, copper, manganese, cobalt, and so on are relatively binding, so what you put in is what you get out. Eventually--the bonds are tight on many of those.

The major positive of compost is the organic matter. Added to your soil, it'll happily bind any positively charged resources that come into contact with it up to its limits (which are rather high). And worms like it, which means you're getting some fertilization from their digestion, plus aeration and water channeling.

As a general rule, since what goes into my pile and comes out of my pile was a recycling of what was already on my property, I don't count compost as a feeding at all. It's just a nice extra to increase OM levels, plus a nice mulching of my newer or more delicate plants to protect against weather changes.

Right now, I'm ditching most of my compost on four new lilac bushes that were added this year. If we get another bad winter, the extra mulching will help them get through without root damage.

Since the nutrients in compost are not very soluble you do not see them appear in nutrient tests, but they are there. Not sure what that has to do with anything. Solubilty has nothing to do with being able to assess nutrient content. The reason you don't see a nutrient analysis (NPK labeling) on most compost is that it is by definition not considered a ferilizer (it is a soil amendment) and so not required (or needed).

My plants always perk up after getting compost, and I don't feed them very much or sometimes not at all, as they seem to do better with just compost. I use a lot of coffee grounds in my compost, but if the compost was very old, it would have less nutrition. I use it before all the nutrition is sucked out of it. But, I am growing plants that don't need a lot of nitrogen to begin with. I like slow steady healthy growth thick instead of fast but sickly, skinny looking growth.

Numerous times, here, I have seen someone recommend sending a sample of compost in for testing just as one would a soil sample. When done the results show very low nutrient levels in the compost, but when that same compost is added to soil and, after a while, that soil is sampled and tested the nutrient levels show a greater increase then what the compost might have supplied if the test result could be believed. The same thing happens when adequate levels of organic matter are added to soils, over time.

I'd like to read one of those threads kimmsr, can you post a link to one of them please.

Lloyd

So, if I get it right, this "bucket of warm spit" brings :

A lot of OM that sustains the soil food web (and absorbs water, creatse air pockets, prevents the soil from erosion and compaction) .

In the soil food web, apart from the macro guys whom we can see, there are saprotrophic bacteria and fungi who occupy the space and prevent the pathogenic ones to develop.

When those bacteria die their corpses become direct food for plants.

What about saprotrophic fungi ? Do you guys know whether some of them are the same as the ones which build symbiotic relationships with living roots in hard times of no decaying matter to eat any longer ?

Then compost brings many micronutrients in an endless circle compost/grass, plants, trees/ grass clippings, dead plants, leaves.

Except that as we eat the fruits and vegetables we produce, then we have to add more than our own trash even when we have great soil.

Does this make sense or is it more complex ?

>>Does this make sense or is it more complex ?

Makes sense.

Over time, nutrients can and do leach from soils as well, so some replacement for optimal plant performance is necessary. I always recommend soil testing if you think something is off, or about every three years even if everything is just fine.

I do mine yearly, but I'm a perfectionist. This year, I had to add some calcium and some boron in the lawn, and moderate calcium and a tiny bit of boron in the gardens.

Our gardens aren't nature, we tend to plant heavily and coddle a bit, so we lose resources faster than a natural setting would. Compost can help replace some of that.

I don't produce vast amounts of compost (the total output of 2,000 square feet of flower garden, mostly), but I've raised OM levels from essentially zip (1%) to very high (12%) using organic feedings and mulch.

The lawn is the same, just without the mulch and with far heavier organic feedings.

Most of my compost goes on the trees in the lawn and the shrubs, which can always use the help.

@Francoise wrote "What about saprotrophic fungi ? Do you guys know whether some of them are the same as the ones which build symbiotic relationships with living roots in hard times of no decaying matter to eat any longer ?"

It's an interesting question. A bit of noodling around wikis shows that there are a few types that play both roles, and of course we don't know everythign about all types of fungi:
http://en.wikipedia.org/wiki/Ericoid_mycorrhiza
http://en.wikipedia.org/wiki/Laccaria_bicolor

But personally my _guess_ is that the whole soil food web/cycle thing is more important - by which I mean that soil with organic materials will have some decaying going on from one type of fungus, and some of the nutrients released by those will eventually end up being used by the myccorhizal types (possibly with many steps in between).

A few people have mentioned closed cycles regarding their garden/property. When looked at that way, if people are the major consumers of the produce of the garden (as opposed to an animal grazing a pasture), and those people are using toilets connected to a typical septic or sewage system, then it's anything but a closed cycle.

I find that it is hard to beat the performance of plant growth using compost, over seasons. I think compost, mulches, etc, in conjunction with some modest use of rock powders if one has leached soils (calcium carbonate, borax, greensand, etc) can easily be all that is needed. In a heavy soil mulch alone could be sufficient, eventually.

>>A few people have mentioned closed cycles regarding their garden/property. When looked at that way, if people are the major consumers of the produce of the garden (as opposed to an animal grazing a pasture), and those people are using toilets connected to a typical septic or sewage system, then it's anything but a closed cycle.

I agree. In my case, with flower gardens instead of vegetables, the cycle is more closed than some others.

Still, compounds outgas into the atmosphere, get leached away by rainfall, may erode slightly, or plants get eaten by insects or animals that don't hang around and meander off elsewhere to poo.

Natural cycles are anything but closed, so monitoring them to readjust with organic matter, or whatever elements are required that time, is smart.

Going back to the initial question, with respect to ORGANIC MATTER (humus), compost is compost, pretty much. With respect to minerals, I would guess that a more varied input stream would produce compost more balanced in micro nutrients, as was stated earlier. e.g. grass + sawdust would not have as complete an array of minerals as it would if you added kitchen and other yard wastes. My own backyard compost was higher in Cu, Mn, etc. than most of the commercial ones when I tested them side by side. This does not mean simple grass + sawdust compost is no good, since organic matter is one of the main benefits.

I think I pretty much summed up the thread. ;-p

One thing I don't think has been mentioned is that we usually use far more compost by orders of magnitude than we would chemical fertilizer (if we were using it). i.e. a bucket of compost may have roughly the same NPK content as a quarter cup of granular fertilizer. Kimmsr makes a good point (IMO) about extractability and the fact that nutrients are there but may not be instantly extractable in a test - especially N, I would think, which is partially bound up in proteins and complex humic molecules.

All I can tell you is, I've been adding pretty much nothing but compost for years, and my garden thrives, including plenty of N - in fact almost too much for the peppers, this year. :-D

I have seen, many times, soil tests change dramatically just by adding organic matter, which includes compost, to that soil. 40 some years ago the first soil test I had done here showed the soil pH was 5.7 and P, K, Ca, and Mg. were very low. One year later, after adding about 6 to 8 inches of shredded leaves to that soil the soil test result was a pH of 7.2 and the levels of P, K, Ca, and Mg were in the optimal range and nothing more then those leaves was added. to the Lake Michigan beach sand I call soil here.
So where did those nutrients come from if not the leaves? I doubt they fell from the sky.

"I doubt they fell from the sky"

Nutreints in Rainfall

Mineral dusts

:-)

Kimm, But those leaves did kind of fall from the sky. They did not grow in your garden, but were brought in from the outside...and that is the point. Without bringing in new compost or leaves, you are not likely to get ahead with just the return of the plant residues from your garden. unless you green manure and cover crop heavily or sumpthin else. New inputs get you there.

So if we wanted to reduce our ecological print when composting, we should use thrash rather than importing ressources from elsewhere.

If it wasn't gross, I guess going to a slaughterhouse to gather hooves, horns, or feathers would enrich our compost. Or perhaps this sort of trash is ending in dog food. Hence cheap dog or cat food could be something good for compost piles, and an ecologically friendly stuff to add.

>>If it wasn't gross, I guess going to a slaughterhouse to gather hooves, horns, or feathers would enrich our compost.

Feathers would be just fine (feather meal is used in many commercial organic fertilizers). The other stuff, including blood meal, really needs to heat in the compost bin, and stay hot for a while to assure that it's well broken-down and all pathogens have been destroyed.

That involves turning a lot during the first phase of hot composting as well to assure it all visits the core.

For me, anyway, that's not possible. So no animal products go into the compost.

Rain falls from the sky and while it does have some nutrient value it is often acidic and could change a soils pH enough to make nutrients unavailable. Tree leaves fall from above, trees, not from the sky, and get the nutrients from the soil the trees grow i8n..
The point is that soil can be improved by recycling yard waste and not spending money on "fertilizers" and the answer to the question posed is, "What gives compost it's nutrients?" is the nutrients are in that material.