Do Earthworms Work Through Clay?

This is a question I've had for a while: Do earthworms work through clay?

I'm working to improve some very poor soil. And what there is does not go deep before hitting a layer of hard clay.

We've added cow and sheep manure for many years, as well as compost, left-over hay, etc. So we are increasing the height of organic material and giving the worms some food.

However, do the worms actually work their way INTO clay?
I assume they dig their way down, take a bite of the clay, say "Phooie!", spit it out, then turn around, and head back up to where the food is better. So they are not actually digging DOWN so deep-rooted plants can go farther down.

Or am I mistaken?
Do worms dig into clay?

If I turn over the soil by shovel and go down four feet, and manually mix the chunks of clay with everything else, will the earthworms, again, work AROUND the clay chunks, or will they break the chunks down?

We do see earthworms in our clay when there is a lot of organic material on top (aged compost and manure)--and we are very pleased to see them, as you might guess, ha!

I do not remember what the numbers are, but worms, like roots, have a limit to how hard of a material they can chew into to start burrows. Hard enough clay is effectively a rock, which they may nibble but will take a long time to burrow into. Other soil microbes and macro invertebrates (ie ants) can help provide enzymes to break down the clay, and in conjunction with plant roots work caverns into it that expand as the roots grow and decompose (and in doing so microbes provide more enzymes to break down clay). Frost heaving can also help fracture clay hard pans that roots, worms and microbes can occupy and expand. This all takes a long time though (as I am seeing with my fruit and nut trees on rocky clay), so a deep soil ripper/yeomans’ plow or hand forking can help a lot to get things going. The key with these in not inverting the soil layers.

I have a clay deficit, so I don't know this first-hand, but my reading suggests they incorporate the clay and the humus slowly.

i was digging in the early spring into some bleak clay and i'd say no earthworms were getting through that. you certainly couldn't find any. its a nearly level grass yard area and there had been plenty of rain, but even the water hadn't made it through. it was eerily dry not far below the surface. i've started digging post holes over a cubit deep all around the place and stuffing them with partially composted organic matter. hopefully water will start being able to infiltrate and the critters will have something on which to chew.

I live in Maine which often has "clay soil". Not as pure clay as some places, but a pretty high clay content. I see worms pretty deep in the soil around here.

I would like to remind people that there are many different kinds of worms, but I believe most can be put in the earth worm or compost worm categories. The compost worms (red worms, red wigglers, etc) stay near or at the surface and love eating things that are being composted. Those are the worms you want to help break down the manure and straw you spread out. The earth worms stay deeper most of the time and eat things that have already been composted. These are the worms that would potentially make holes in the clay layers. As has been mentioned, there is a limit to what they can do.

If the question was simply how to break up the clay layers, I would suggest some deep rooted plants such as asparagus, comfrey, and diakon radishes. These will be able to break up clay soil and get roots down deep. This can help with water penetration as well as worm penetration. The roots will die back and leave little paths for the worms and water to follow deeper.

David,

I live in an area with pretty solid, brown clay.  More to the point, the school I teach at sits on even harder brown clay as all of the topsoil was removed.  But after every rain, we get hundreds of worms crawling across the pavement.  I assume that they came from holes in the clay as there is virtually no organic matter at our school.  At my house, the worm tunnels do go quite deep.

Eric

I have crazy orange clay (think baseball diamond-- where i live used to be a sand quarry, they took the sand and left the clay) and when i dig out large amounts to make a hugelbed I do see worms in the clay maybe up to 10 inches or a foot down sometimes. but like other folks here, I also make a concerted effort to leave a lot of organic matter up top for the worms to eat, and I bury things in trenches, plant deep-rooted species like burdock and daikon, etc.

When i google max root pressure, I get 0.5 MPa, or 75 psi. How much is that really?  If the effective area of one finger in the soil was say 0.5”x0.5”, that’s 0.25 in^2.  If you could lift a half gallon of water with one finger thats 4.15 lbs. so, 16 psi of pressure. How much is 75 psi?  Maybe the weight of your arm resting on the tip of a screwdriver?  I don’t know, figure out what measurement makes sense to you.  Pressure is force divided by area.

Okay so tillage breaks up soil, but yearly tillage degrades soil and causes plow-pan/compaction. The best practice currently seems to be to have one “deep ripping” (Geoff Lawton’s words) till, with I don’t know a chisel plow or something, and then no till from then on.  

As you say, why would a worm or plant roots push hard into infertile soil?  Unless it needs water, otherwise maybe there’s no point. It wants organic matter, food, soil life; clay, not so much, unless it has these things in it, or unless maybe it’s a pioneer legume tree and grows its own rhizobia.

Hi Mike,
There is a difference between something like rototilling compared to using plants to break up the soil. In one case, the soil is being lifted and chopped and turned over. This destroys much of the microorganisms and fungi in the soil; and those things are needed to make nutrients available to the plants. It also brings weed seeds to the surface. I would agree that this type of "tilling" should only be done at the start.

When we talk about using plants to till up the soil, it is a very different thing. Typically the plants are grown and either allowed to rot/compost as is, or they have the top cut off, and the roots are allowed to rot/compost. In both cases, the soil is not disturbed, and as the roots break down, it creates little paths for things to follow, allowing water to penetrate deeper, and allowing worms to go deeper if they wish.

As to why something would go deeper in clay soil... is for the nutrients. There are many minerals in clay soil, and the plant is in search of those as well as the things it gets from the topsoil. Nutrients tend to work their way down in the soil, and deep rooted plants can bring those back to the surface for more shallow rooted plants to use.

Interesting note, that plant roots can use chemical means to break up rocks by exuding an acidic substance, as well as using the physical means of root penetration to break apart rocks.

Matt, I know all of that. Not sure we’re answering the original question:  Will hard clay breakup naturally or not, and if so, how long will it take?  

I can give a sideways answer to Mike’s post.  My hard-as-brick brown clay turned sponge-like after piling woodchips on the surface and letting them sit for a year.  Adding mushrooms sped up this process on a different bed and I imagine that building a compost pile would have similar effect.  Just piling up organic matter should encourage worm activity and get that soil loosened in quick order.

Eric

I have worms in my clay soil.  You can help a great deal by giving the area a good broad forking initially.  I like to pile on as much organic material as I can and broad forking it in deeply.  If you do this with raw wood chips, don't expect to grow anything for a year or two.  If you use compost, you can plant it immediately.  In either case, worms will thrive, much more so than in plain clay.  If you mix coffee grounds as well, you'll have more worms than you know what to do with.  So, in answer to your question, in my case, the worms will work through the clay.  I find worm holes throughout my clay.  That said, they will do much better if you break the clay up and mix in organic matter.

I'll back up the "not all clay is the same" bit - I've got an area of land where the former owner's son-in-law dumped, compacted and levelled an area using subsoil from his pond-digging company. So there is a lot of clay with rocks and I even found a rubber duckie! And it is seriously hard stuff!

Even our regular subsoil is pretty much compacted glacial till except where the bedrock is near the surface.

Yes - we've got a type of worm that "hibernates" in tunnels in that inhospitable dirt both when it's cold and during the summer drought.

No - water does *not* infiltrate worth beans... even after the heavy Nov. rains, there are areas where the ground is dry just 6-8 inches down.

No - roots like daikon don't infiltrate it well. They will try only as much as they have to, but mostly spread out on top.

Yes - tree roots do spread through, but they take a *long* time to do so.

Yes - I've read recently about the many minerals that can be found in clay, but again, that can be quite inconsistent. For example, my island is low on selenium, so most farmers supplement their animals or they may run into trouble.

However, the 'dig a bunch of deep skinny holes and fill them with compost' permaculture system does seem to do a bunch of good. Since I'm digging by hand and we have so many rocks, I tend to get a wider hole and often consider myself lucky to get it 1 foot deep, but it not only gives worms a deep area to hang out when it's hot and dry, if we get rain, the rain can infiltrate starting lower down.

Roots seem to sense when there are goodies to be had, so I often try to dig some of these compost holes 5 feet from a newly planted tree.  I'd aim for 3 ft from the drip line for a mature tree. I often put punky wood in them to decompose slowly and hold moisture longer. In my area, tree roots are often found "harvesting" good things from old tree roots in the soil from long-dead trees.

The digging is so difficult, I haven't done as much of it as I would like. If your clay is really tough, you may find a broad fork just won't go through it. The type of tractor blade that might be helpful would be the one used for Key Line Plowing - it opens up grooves and doesn't "turn" the soil, but where it was tried on this island, it was done over a three year period, going deeper each time.

Not sure why this is, but I find the biggest nightcrawlers in my garden, in the top several inches of clay.  I have a relatively small backyard in Oregon's Tualatin valley where we have a clay silt soil. We get a lot of rain, about 40-50 inches a year, but essentially none between mid-June until mid-September. I have 2-3 foot wide planting strips in the garden, where we removed about 30% of the clay in the top 16-18 inches, and worked in sand and compost. There are clumps of clay in this zone. When I dig in the strip, almost all the worms are in the clumps of clay, and especially in clay at the bottom of worked section.
My hypothesis:  that nutrients from the compost are washing down and being absorbed at the clay surfaces, which seems to promote fungus growth at the clay boundary. The very large earthworms in my garden seem to be eating this fungus or microorganisms on the wet clay surface. If I break apart a six inch clump of clay, I invariably find several large fat nightcrawlers in the clump.
Seems that when I add cardboard, or other moisture retaining materials, I find the earthworms there as well.
I wonder if I add biochar pieces, would I find earthworms next to the biochar surface?
Of course for this to work, there needs to be a constant supply of composting materials above these earthworm feeding zones. Is this perhaps why Amazonian people used Loma Preta biochar + composting systems?