I have been growing for years in the Mid-Atlantic region in tan and now red clay soils. I prefer to initially mix heavy amounts of organic material with the native soil to spade depth to produce an amended soil that will allow both water infiltration and drainage. I rely on night crawlers to move organic material into the subsoil and break any hardpan and I layer organic material onto the surface or lightly till it into the top couple of inches of the soil in subsequent years. Often what is incorporated is a layer of organic mulch that had covered the surface the previous growing season. The addition of the organic material to the mineral component of the soil results in weak organic acids helping to weather the mineral component and the clays, since they are charged electrically, tend to hold onto or adsorb many of the positively charged ions. I feel that by layering the organic material above the native soil that there may be some time before there is a good mixing of the two substrates and water conductivity between the two can be harmed due to the textural differences. Water is moved upward by capillary action and the two dissimilar textures can negatively affect that movement. It is true that soil organisms over time will complete that task but I am impatient and want results now. Whenever possible I try to grow an initial cover crop of a grain and a legume that has be innoculated in order to establish a good microbial population and prepare the soil for the crops that will follow.

Is it truly possible to have too much organic material in soil?

Technically speaking, it is all organic - even the mineral soil. ;)

Is it possible to have too much compost in the soil? Probably not. Many grow/garden in straight compost and it is the foundation of the Sq. Foot Gardening method which is also quite successful as well as Lasagna Gardening. How well the plants do all depends on the quality/components of the compost.

Personally I prefer to max out at about 20% compost.

Dave

If I recall correctly, the 10s of thousands of acres of "muck' soils south of Lake Okechobee (sp?) are about %60 organic matter, very high at any rate. Those soils are very productive if managed properly, they have also been depleted by many feet by commercial agriculture in the area (mostly cane growers). Thanks to the poster (whose name is forgotten) who mentioned the critical nature of soil interfaces, never seen that mentioned here yet but very important.

Yes you can, but most of us do not add enough organic matter to reach that point. If you get over 10 percent, really difficult to do in my experience, you could start releasing pollutants into the ground water system.

Technically speaking, it is all organic - even the mineral soil. ;)

What, I say, what in the world is your definition of organic?!?

what in the world is your definition of organic?!?

The word "organic" is one of those used to mean many different things to many different people - thus the word "technically" in my comment above. Why, what is your definition?

There is:

# anything "natural" as in found in nature
# anything NOT synthetic in origin
# anything relating or belonging to the class of chemical compounds having a carbon basis; "hydrocarbons are organic compounds"
# organic foods - foods that are produced according to certain production standards
# being or relating to or derived from or having properties characteristic of living organisms; "organic life"; "organic growth"; "organic remains found in rock"
# involving or affecting physiology or bodily organs; "an organic disease"
# of or relating to foodstuff grown or raised without synthetic fertilizers or pesticides or hormones; "organic eggs"; "organic vegetables"; "organic chicken"
# simple and healthful and close to nature; "an organic lifestyle"
# a fertilizer that is derived from animal or vegetable matter

etc. etc. etc. ;)

Dave

Michael wrote: Thanks to the poster who mentioned the critical nature of soil interfaces, never seen that mentioned here yet but very important.

By soil interfaces, do you include the interface between topsoil and subsoil?

Regarding levels of organic material; I had put a lot of homemade compost, coffee grounds and old horse manure into some garden beds. I suppose I should till them but I'm reluctant to disturb the beds now that they're established.

Eventually, I'm sure the organic material will break down and the levels will return to something sane.

thus the word "technically" in my comment above
"Technically speaking" does not mean "apply any definition you feel like using". It means you are using the proper "technical" definition.
# anything relating or belonging to the class of chemical compounds having a carbon basis; "hydrocarbons are organic compounds" is the correct technical definition. The mineral portion of soil, technically speaking, is not organic.
I realize it's semantics, but proper semantics help us avoid confusion.

Technically, anything relating or belonging to the class of chemical compounds having a carbon basis; "hydrocarbons are organic compounds" is only one of several accepted definitions of "organic" and not always listed as the primary one at that. So technically, most of Dave's list of definitions are equally as valid, including anything natural, as found in nature.

Semantics aside (not that they are particularly relevant in this situation), the term "organic" is not a simple one with a single defintion and in this case with the topic at hand, referring to all garden soil as 'organic' or naturally occurring makes sense. However the question was directed at the volume of 'organic matter', which is a different issue altogether, organic matter having its own specific definition.

From Wikipedia Organic matter (or organic material) is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for.

I agree with this definition. When talking about soil, organic matter refers to the decomposed or decomposing once-living organisms. The mineral portion - sand, silt and clay - is not organic matter.

And yes, I think that there can be too much organic matter in soil. Some plants like a leaner soil and do better without a lot of nutrients. Even for those plants that like a rich soil, they may not be able to use all the nutrients available. As a result of too much organic matter, nutrients will be lost to the air and to leaching.

Well the original question was about organic material in the soil, not organic matter, so unless the OP is a geologist, theoretically an argument could be made that all the components of dirt are organic as in "found in nature and not synthetic" but it was just a smiley face comment to begin with so no big deal.

And if we want to play semantics - a game I personally love and often indulge in here when pointing out that an old pile of a single ingredient such as manure or leaves is NOT compost (tho many insist on calling it that) - then we can add even more definitions to the list including now the one from that renown source, Wikipedia.

The point being there are many different interpretations and applications of the word organic as well as for material and matter (shades of science fiction) and while clarity is somewhat important in a format such as this, it is likely that the sun will still come up tomorrow. :^)

Dave

Idaho gardner: I was refering to interfaces where the two textures are very different and the impact on water infiltration through them. For example, a coarse sandy soil sitting on top of a clay soil with a very smooth, abrupt interface (no co-mingling of textures) will hinder the passage of water through the soil profile. I believe it has to do with the difference in pore size between the 2 soils.

Michael,

I can think of two such interfaces right off the top of my head.

First would be the interface created by the addition of organic material into a clay topsoil and its effect on the porosity of that topsoil. The upper layer of soil might become porous and the soil just below that would remain more clay-like.

Second would be something I see in my yard; In some places in my yard, I find a caliche layer under the layer of clay topsoil and clay subsoil.

The issue of water movement would militate a more aggressive program of soil amendment to improve the interface. By more aggressive I mean double-digging or other deep tilling techniques when dealing with clay soils. Double-digging would improve the migration of humic and fulvic acids and other organic by-products into the lower layers and speed up the process of soil conditioning.

Organic, to a chemist, would mean of a carbon based substance, put quite simply.
Organic, to a gardener, should refer to using once living substances to improve the soil, to leaving the soil (and therefore the world) in a better condition than was found.

Here is a link that might be useful: OTA definition of organic

when cow and horse manure stops producing a good garden
for me then I will try to figure out what all this hi tech talk is about. [just an average gardener with a GED)

ED

"... a coarse sandy soil sitting on top of a clay soil with a very smooth, abrupt interface (no co-mingling of textures) will hinder the passage of water through the soil profile."

I think we need to look at this statement a little more carefully so we understand the dynamics. We know that a sandy soil gives up water quite easily, and clay soils have great capillary attraction. The tendency is for the sand to immediately give up it's water to the clay. If it was dry, the clay could easily absorb the water. We're not really dealing with an issue of the 'want' of water to flow into the clay - it does 'want' to. We're dealing with the clay as a physical barrier to percolation.

If we hold a sponge with the long dimensions horizontal until it stops draining, and then set it on a stack of paper towels, the towels will drain all of the water from the sponge that is not so tightly held that the capillary pull of the towels cannot overcome it.

Similar to sand over clay (more porous over less porous) is a container soil over a layer of sand (we wouldn't do this, but let's run with the illustration), or a raised bed soil over clay loam. We know that the raised bed soil is more porous than the clay loam, and the container soil is more porous than the sand. In both cases, the water will easily make the transition from the upper, more porous strata to the lower, less porous strata.

Let's imagine that the container soil in the upper strata supports a 2" perched water table (PWT), and the sand supports a 4" PWT. If we have 4" of sand in the bottom of the container, the container soil will still have 2" of perched water, but if we increase the depth of the sand to 6", we will have no perched water in the container soil, and the top 2" of sand will also be free of perched water.

The clay is actually a physical barrier (much like concrete would be) because of the extremely slow percolation rate. The clay loam would offer faster percolation, so should present no drainage issues, as long as it's not saturated and a physical barrier because of slow percolation.

As long as the lower strata allows water movement, there is no impediment to water flow when a coarse media is stratified atop a fine media. We cannot say the reverse is true, however. Media that is fine enough to support a PWT will only give it up to the underlying strata IF the underlying strata is made up of particles Al

Oops, had my textures upside down. Clays with their stronger capillary attraction than clays can pull water from sands right?

So we don't get bogged down by someone arguing the impermeability of clay because of it's slow percolation rate, let's say that a fine substrate below a coarser layer allows free water movement into the fine substrate as long as there is room (porosity) in the fine substrate.

Al

If you have never tried to drink water from a well that gets its water from under a swamp, fen or bog, and could not get past the smell of that water to notice that the water tastes like it smells, you probably cannot quite believe that you can get too much organic matter into your soil. It is possible to get too much OM in soils, difficult, but possible.

Regarding capillary action in clay soils, the clay soil's permeability could potentially be (and probably is) altered by the leaching of humic and fulvic acids. These acids would bind with the metals in clay and interfere with the stickiness. (They also make nutrients available; they chelate Mg, Fe, Ca, and other 'micronutrients' needed for plant growth.)

I'll bet that would also apply to caliche; caliche treated with humic an fulvic acids will probably dissolve into clay. That should be easy to test.

So, heavy use of organic material in soil doesn't just provide nutrients for fungi, bacteria, and ultimately plants, it also modifies the mechanical properties of the soil, and in particular, with the movement of water in soil.