Our native soil, here in Madison, Wisconsin, is high in clay, but not so high that could be directly used for pot making. It is hard to work with in the spring, when it is wet, due to clumping and sticking. I have been making compost, and adding it to our small garden plot, for 15 years. The garden soil is now easy to work. We have a large maple tree, and I shred the leaves every fall, to put on the compost pile. In the spring, I dig out the finished compost, from beneath the pile, and the cycle repeats. Clay soil is high in minerals, and it holds moisture well, so it has some advantages. But it can be hard to work with, that's for sure...

Try more compost and something to help soil breathe like coarse vermiculite or sand.

No, I don't think it will slow down. Might even speed up. At least in theory, the more organic matter you feed the soil, the healthier the soil food web becomes. That healthy SFW gobbles up the organic matter.

Karen

Try adding coarser things like shredded leafy branches, chippings and the like. They last longer.

Try adding coarser things like shredded leafy branches, chippings and the like. They last longer.

I thought about that but am worried about 2 things.

First, nitrogen tie-up? I don't seem to have a problem right now, even with all the leaves, but I read many bits of advice here about a woody mulch tying up nitrogen if mixed into the soil.

The second concern is how it would affect my root vegetables with chunks of wood in the soil. I grow a lot of carrots, beets, garlic, etc. and rotate them every year so I like my beds to be as rock-and-wood free as possible so nothing blocks their growth.

Keep up the contribution of organic matter. Add some grass clipping and manures to your leaf compost; lowers the C:N ratio while contributing nitrogen. Avoid woody ingredients larger than woodshop sawdust; it can take years to finish (hihgh lignin content) decomposition. The organic matter is not supposed to last years but merely seasons.

You have given good stimulation to the soil organism population and they are doing their job well.

Minimize your cultivation and maintain the soil improvements. Work only the 3-4" of the surface as preparation for seeding or transplanting.

Your challenge now is obtaining sufficient organic matter to keep pace with the need. You should find that as humus accumulates there is less need to apply high amounts. Be content if you achieve 5%. You can 1/2 fill a quart or gallon jar, top with water, shake and allow to settle out for 12-24 hours. Measure the layers of separation - sand at bottom, then silt, then clay and finally the organic matter on top. Do a bit of math and determine each layer by percentage. 5% organic matter is your target.

I have four compost bins on the go. Each when finished is run throw a rotary tumbler to remove any unfinished materials which are returned to a bin. When applied to the beds I merely scratch it in with a hand cultivator.

Last year I had carrots in the 12-14" range. A few were deformed and likely because of some stones in my sandy soil. Some years I will loosen beds with a fork to remove stones of any size. The organic matter does the rest.

Be careful with the peat moss as it will lower your pH. A little will help until you secure sufficient organic matter for spring and fall amendment.

You are doing well. You should be seeing improvement after four years if you make the comparison to year one.

I've had a vegetable garden since about 1996 or 97. I live in middle Tennessee and have some nice red clay. I am no expert in the matter of soil or adding amendments but I can tell you what works for me where I live.
My garden is 15' x 44' and I make enough compost each year to cover it with about 1" of compost. I also add any organic matter I can find like shreaded leaves and grass clippings. I don't worry about weed seeds because I save enough shreaded leaves to keep the garden mulched during the summer.
This has changed my hard red clay into some really nice, soft, dark brown, almost black, CLAY! It's 100% better than it was when I first started, but it's still clay with a lot of organic matter in it.
Don't think that adding amendments once or twice will solve all of your problems. I do it every year. I have to do it every year. If I don't there is less organic matter each year and the clay starts to get hard when it's dry and sticky when it's wet.
I hope this helps a little.
jim_6b

Kinda strange, since I have always understood that sandy soils burn amendments while siltier and clayey soils hang onto OM. Which is supposed to be one of the reasons that the latter soils generally have higher native fertility than the former.

I have the same problem and sorry don't have a magical answer, just sympathising with you. Last spring, I rotovated in a huge bale of peat moss in one part of the garden and it made the soil just wonderful. I grew large, healthy parsnips, leeks and beets in this area. Next year, I'm going to use more. I have lasagna beds but too big a garden, so try different things in different areas.

wood chips do help the older the better
nitrogen tie up can be counter acted with more nitrogen

Your clay soil is not "eating" up the organic matter you put in, it is the Soil Food Web that is doing that and they reason there does not seem to be any left at the end of the growing season is because your are not putting enough in.
Have you done a test for humus (residual organic matter) in your soil lately?

I've gardened in clay (brown and gray) in MO since 1991. It was awful when we started. As soon as you stop adding amendments the texture begins to deteriorate. Here's what we've done;

Veg. garden - raised beds to promote drainage - didn't buy topsoil other than a few bags here and there - compost dug in annually, mulch heavily with leaves/grass - got hold of a cubic yard of river silt/sand, layered into compost piles right on the beds, dug in following spring - made a huge difference. If you're going to do that last one don't skimp, otherwise sand + clay = concrete. We now have 12" of nice dark soil, still clayey but the garden grows pretty good. The beds are up about 4"

Perennial beds/trees/shrubs - piled on the free city yard waste mulch, spring and fall, and let the worms do the rest. There's some nice dark soil in those beds now also.

It's a labor of love, clay is.

Try keeping the soil covered with mulch, maybe shredded leaves.

My clay soil is also absorbing the organic matter, but at least the soil is changing color and becoming friable.

Sounds like you got a good system going.

I just keep adding organic matter to my clay soil. It gobbles it up also.

Nothing comes close to lasting 4 years let alone 10 years like you ask in your post.

Sorry, just keep adding organic matter.

Adding the organic matter in any form is recycling the nutrients removed by harvested crops. The organic matter return must be sufficient to equal or be moderately surplus to the nutrients removed by harvest. In agricultural terms it is called nutrient management.

Some of the nutrient are taken up by plants. All of the organic matter does feed the soil organisms who in the process of decomposition make the nutrients available to the plants. Any surplus is converted to humus and remains stable until the supply of organic matter drops below plant demand. Keeping the organic matter supply equal to the demand is the main objective.

The growth of your plants and the average or better yields are your indicators. If either measure drops then you need to look at further organic matter supply and/or if there is a nutrient imbalance; soil test. With good organic matter in the 4-6% you should not find many natural deficiencies or excesses unless you are trying to grow a plant with exceptionally high demands.

Keep your organic matter in the upper 4-6" of the soil where it is accessible to the organisms. Any deeper and the roots can not access it, besides placing the organic matter in a anaerobic position with another level of organisms.

One thing about clay, it's said to be very nutrient-rich and fertile because of the huge number of ion-exchange sites on the clay particle surfaces. It just has crappy physicaly properties.

As others have said, you just have to keep going. I have 4 compost heaps. I add leaves in autumn and bring in 8 - 10 sacks of manure every couple of years as well. I have had this garden (ca 15 x 45 feet) for about 19 years and have add organic matter to it continuously and expect to continue to do so. (But please don't use peat. I don't want to start the usual heated discussion so I'll stick to saying it has no plant nutrients and costs you money.)

One important tip - never stand on clay soil when it is wet. It will become solid when it dries out.

And if you dig, you will need to wait for the optimum moment in spring when the moisture is right. Too wet and you will have back breaking work and clumpy soil. Too dry and it will be like digging concrete.

Adding compost to *any* garden soil is a continuing process IMO. The organisms require feeding as do the plants so it's not going to remain in the same state as when you added it for very long. I find that when I mulch with my wood shavings based compost in early summer that the only thing visible by fall are a few shavings. I need to mulch twice a year. I have lots of hungry earthworms to feed! The good things are that my plants grow well and are healthy and the soil seems to be improving in some areas. Of course I keep enlarging the garden so it's difficult to keep up - but I'm trying! ;-)

This reminds me of something Liz Drouett said in her book, Organic Rose Growing (Growing Roses Organically? it's been a few years).

She said that our famously bad heavy clay soil does indeed gobble up organic matter & that it always will, but that, as time goes on & you keep adding OM, the soil's appetite abates, going from ravenous to "a constant case of the munchies".

Hi All, I do not know if the quote and link below sheds any light on the subject. Maybe some more knowledgable can explain how you can calculate to get to the ten to one ratio in the soil. I found Azotobacter interesting as I have been studying Azo and others recently. Best regards.
From: Earth's Green Carpet
"He has further to remember that the amount of combined nitrogen in the soil is in relation to the amount of carbon. The relation is 10 of carbon to 1 of nitrogen and is known as the carbon-nitrogen relation. It is the desire of Nature to keep this relation stable, and should it alter she at once sets to work to restore it. This means that any additions to the soil of organic matter (containing carbon) or of nitrogenous manures set up a whole series of fresh movements among the microflora, to whom is assigned the task of keeping the soil in condition."

Here is a link that might be useful: Http://www.journeytoforever.org/farm_library/greencarp/greencarp6.html

I clicked the link but found the reading a bit too broad in its scope to be very useful.

But your reference to Azotobacter was interesting. I'm assuming that it uses some sort of carbon-based material as food, but it is a naturally occurring nitrogen-fixing bacteria that seems to be ubiquitous, found world-wide.

Here is a link that might be useful: Azotobacter

Anyone have experience with long term (say 10 years) soil amendment?

Yes, but we have to define what kind of amendment we want ;)

The organic matter gets 'eaten', not by the clay soil, but the organisms in that soil. That organic matter doesn't last long is actually a very good thing even though it feels like lots of work. The decomp of the OM leads to increased fertility as well as formation of humus which aids in keeping those tiny clay particles from sticking to each other. The OM break down also leads to improved tilth which is simply individual soil particles getting glued together to form larger particles by secretions from the soil critters as they do their thing. This improves drainage and enables more oxygen to reach into the soil and nourish roots.

However, if despite all the advantages of using OM to improve soil qualities you still wish a more permanent way to improve drainage/aeration of the soil and reduce the rate it compacts/clumps etc. then you can use a product called Turface. It's a calcined clay product used for sports fields. Unlike the clay you have now, this is fired at high temps so it remains very stable and never becomes 'muck'. It's not like pebbles that have no internal porosity either, it's incredibly porous. A substitute would be calcined DE which is sold by Napa Auto Parts stores as 'Floor Dry'.

You can read more about Turface here. Click on the tab at the top "Where to buy" to input your zip code and find a local source. It lasts, literally, forever.