Building heavy, acidic clay soil (ultisol)

Hello All,

Longtime lurker and I've learned a ton from all the discussion on these forums.  Thank you all already for the wonderful community and knowledge that is shared here!

I've moved to a 10 acre future self-sufficient paradise about 3 months ago in the piedmont of North Carolina, but the soil is going to take a bit of work to become productive.  My goal at this point is to build/improve the soil as much as possible in the front 3 acres between the house and the road to eventually transform into a food forest.

The soil itself looks to be an ultisol, and is quite acidic overall (see soil tests, attached).  Organic matter is <0.5% and also lacking in potassium and phosphorus.  Unfortunately, my soil test does not give me an idea of the calcium present, but I'm guessing it's almost non-existent as is typical in these soils.  Digging down in the soil was quite difficult with a post-hole digger, and you can see there is no visible topsoil.  Parts of it that I've broadforked have come up in very large, hard, heavy chunks.



Here's what I'm thinking for a general process for site prep -

Mow as close to ground as possible
Throw down a ridiculous amount of gypsum (essentially a thin layer covering the entire surface)
Add 3" or so of woodchips or compost (whatever I have on hand at that point)
Broadfork, trying to break up the deep clay as much as possible.
Add another ridiculous amount of gypsum, also lime, potassium sulphate, and bone meal
Surface cultivate 6" or so as finely as possible
Layer on more woodchips or compost

Then, after a year or so, start actually planting the food forest plants into these more intensively cultivated areas.

I'm unsure about a few things with the above strategy.  I know that putting wood chips deep into the ground is generally frowned upon with regard to nitrogen robbing and anaerobic decomposition, but if I want to get deep organic matter quickly, this seems like it could work, as I've read stories here about how these dense soils prevent even tillage radishes and other cover crops from penetrating.

Another thing that's crossed my mind is biochar.  I don't have any experience making it, but I'm not sure how much of a difference it could actually make.  Considering the current state of the soil, it might be a good idea to include a layer of biochar before I broadfork to get microbes down deep with the wood chips and gypsum?

Also, would there be any point in adding the potassium and bone meal at this point?  I'm wondering if it would be wasted since there's no organic matter in the soil to prevent it from leaching out.

Any thoughts and critiques are appreciated.  I still have a lot of parts of overall design that I need to work on, but I have a few small areas I have plans for now, and I'm anxious to get started since it'll take a while to get the soil up to snuff!

Thanks!

Chris

Howdy Chris, welcome to permies!  I didn't see the attached soil test but it looks like you could use all of the organic matter you can get ! I wouldn't worry about the nitrogen loss for now, can you get any manures ?

Welcome to the posting side of permies, Chris !  

That's some serious looking hard deep clay!  Clay is the best at retaining nutrients (as it lays in microscopic plate like layers and has the highest cation exchange capacity, drawing nutrients into it, so don't worry about leaching, especially in soils which are that dense.  I imagine if you had a hard time with the post hole digger, it may be challenging to broad fork or till.  How much land are you thinking of working?  What is your final goal with the land?  If you are planning to establish trees, then I would definitely focus on working the planned location of those tree spots, and not on the larger area around them.

You may still regret putting wood chips into your soil, even though you clearly need to get some organic matter in there.  I would recommend against it, and concentrate on adding the chips all in one final mulch, as I will address.  

Do you have a chipper?  

Access to manure, as Miles suggests, is a big bonus.  Some sand in the top dressing before you broad-fork all of your amendments into the soil might come in handy, especially if you have enough organic matter.  You don't want to add sand if you think you don't have enough organics, as you might end up making concrete of sorts, but a small amount of sand can be a huge blessing to help break up clay if the organics are keeping things somewhat humusy.  At any rate, adding properly inoculated biochar, if you can make it, will boost your system, as it will alkalize, as well as adding aeration, an aggregate structure, micro and fungi habitat, and moisture retaining physical and biological structures.  

You definitely need organic matter and the liming agents, and broad-forking might be the best way to incorporate it.  Six inches seems like it would be a lot of tilling, considering what you are working with, unless you have a lot of amendments to blend in to it.  I'm a no till guy and would suggest not doing it at all, but if you are I would concentrate on shallower tilling and in smaller areas, rather than your broader landscape, and I wouldn't mow your weeds just yet.  They are better off aiding you in the transition, as nature is using these particular adapted species to heal that land back to a covered surface.   If I were you I would just add your top soil amendments, and broad-fork them in, adding seeds, root cuttings and transplants as you go.  I would recommend rye seed, and other deeper rooting plants like the tillerage radishes you mentioned as well as dandelion, chicory, maybe comfrey...  These will chase the broad-fork tine corridors that are now dressed with your amendments.  Water this well, and wait for it to get established, and broad-fork again and add more seeds and water well again.  Allow the plants to re-invigorate after the broad forking and for the seeds to gain a good stronghold.  Add worms of all sorts.    

If you have a chipper, then chip up some of your chips, reducing them in size.  If you have manure, or other heavy nitrogen organic additive than add that to these reduced chips.  Add these fine chips as a top dressing of your twice broad-forked soil amendments/tilled and seeded areas around established plants.  Water well.  

Wait.

Then chop and drop your weeds with a hoe, and add bulk heavy chips over your weed spots, leaving desired plants to gain more ground.  Water again.

Remember it is vastly better to spread amendments thickly over a small area, than thinly over a large area.  You will be rewarded much quicker with focused intensive activity than with a less intensive more thinly scattered situation.

Not sure why the soil test didn't attach, Miles.  I'll attempt it again with this reply.

I think I'd likely be able to get a good amount of manure.  My neighbors have horses and chickens and I wouldn't be surprised at all if they'd be willing to let me take a bunch.  Sadly, without a tractor, it'll likely be slow going, but hopefully I'll be getting a tractor in the next few months.

You certainly hit the nail on the head with your comment on the digging of post holes, Roberto.  Each 18" hole took about 15 minutes to dig, but it was necessary to put in the posts for a deer fence to keep the critters out after they scalped my partner's sunflowers.  I experimentally broadforked early on and it was quite the chore, even in slightly damp soil.

I'd like to work on the front three acres first, considering that's mostly open field with a few stands of trees.  I'm just letting the vegetation there grow, and it's actually filled in quite a bit, which is encouraging.  When I mentioned mowing before, I was referring to the areas that I was planning on intensively cultivating for site preparation, but the field itself I'm leaving alone to encourage growth.  I am considering chop and drop though, as much of the early vegetation in the field has gone to seed, but I'm not sure if that would encourage new growth or just kill what's already there.  Right after I moved in, I broadcasted a large amount of this High Diversity mix  over all of the fields, but I didn't see anything recognizable come up from it (though it's 100% possible I wouldn't recognize anything if I saw it).  I was excited about moving in and wanted to do something, so I figured a good experiment would be to broadcast this and see what the land wanted to grow.  Perhaps chop and drop would help to provide a thin mulch layer that would help the germination of the seeds that would come up this this time of year?

In the end, I'd like to have self-sufficient a homestead as possible, growing 90% of our own food, including pigs, chickens, and possibly goats or a couple cows.  I have no illusions that I'll still likely buy cooking oil, coffee, chocolate, and the like, but I'd love to be able to be self-reliant for everything else.

No chipper, sadly.  I've heard both the blessing and curse of adding sand to clay..  I think I need to do a bit more research before I add it.  Maybe the trick is to build up the organic matter a bit before adding it.  I'd hate to try to do too much of a good thing with it and end up with even more of a problem.

I'm at heart a no till guy too, but I'm just thinking of the initial break-up of the soil when I talk about tilling 6".  My thought is that there's so much solid clay, I'd get more bang for the buck by doing an initial broadfork and till with the organic matter and biochar to get it as evenly distributed as possible, then no-tilling thereafter and continually adding to the mulch layer.

Thanks very much for the advice so far - you've given me a lot to think about.

Mow as close to ground as possible
Throw down a ridiculous amount of gypsum (essentially a thin layer covering the entire surface)
Add 3" or so of woodchips or compost (whatever I have on hand at that point)
Broadfork, trying to break up the deep clay as much as possible.
Add another ridiculous amount of gypsum, also lime, potassium sulphate, and bone meal
Surface cultivate 6" or so as finely as possible
Layer on more woodchips or compost

hau Chris. I would like to make some suggestions about the above proposed methodology.

If you are going to broad fork, why bother mowing? That is a waste of fuel. Instead of mowing use that fuel money for some fungi to add to the soil, acidic soils usually have more bacteria so adding fungi will get you closer to good soil.

Since that soil in your test hole looks fairly compacted you would do better to pay a tractor to come and turn the soil after you lay down the gypsum and I would pass on the lime and potassium and go more for the bone meal and compost to complement the gypsum.
Hiring a tractor to do this one time turning under not only incorporates your amendments and breaks the compaction but it also will open many air and water channels without killing off all your current soil microbes.
Tilling to a fine texture will kill your soil organisms, leaving you with dirt, which means you now get to start from scratch to build soil (biologically activity is what makes soil out of dirt), this will cost you time, some money and is totally in-necessary.
Adding wood chips, biochar and compost are very efficient ways to get a carbon cycling going in any remediation project and they will give food to the microbiome organisms, allow water infiltration and oxygenation to occur, the triple win scenario.
Once you have broken the compaction and made the organic amendments it is time to seed so you can get roots into the new soil, it is also a good time to soak with a compost tea to add not only even more humus but to increase the microorganism population.

Remember that soil testing is set up for non organic farming, it is not designed for any method that doesn't include chemical fertilizers and it doesn't take into account the effects of microorganisms.
Following a soil test set of recommendations is great if you are a chemical bound mono crop farmer, but if you are going to build a food forest, it might not work well for your intended end goal.

Redhawk

Not sure why the soil test keeps dropping - I think the forum doesn't allow .pdfs.  I'll try again on this post with an image attachment.

Hello Bryant, thanks very much for your insights!  I, of course, have more questions 🙂

My thought on mowing before broadforking was mostly for access.  Most of the area I'm looking at has around 3' of grass/brush growth, which, while encouraging to see, makes it difficult to put down soil amendments.  I've been thinking about picking up a scythe for the last few months for chop and drop purposes, perhaps this would be a good time to do so and save on fuel as well.

When you say use the fuel money to add some fungi to the soil, I'm not sure what you're referring to.  Mushroom compost?  Quick research on that does seem like it would be beneficial on my soil, being high in humus, chalk, and also more on the alkaline side, though it sounds like the real benefit is the residual fungi present.

Why would it be best to skip the lime and potassium at this point?  My soil test (hopefully attached this time), indicates a deficiency in potassium and a high acidity (~5.0 pH).  I'm assuming that the soil building steps I'm taking will have the more or less same positive effect, rendering these amendments unnecessary?

Regarding the tilling, point well taken, I certainly don't want to kill the microbes I have there already.  My main concern was the large clods of clay that came up while broadforking.  The picture below isn't the best, but you can see that large chunks of clay were coming up 6" or so from the surface.  My thought was that the soil would build more quickly/evenly if the compost and/or chips were mixed in.  I suppose if I put down the wood chips/compost before broadforking, the surface could have been more even.  The area pictured here I scattered the cover crop mix on that I mentioned before, but nothing ended up growing.  I didn't use any amendments here outside gypsum, so I think compost to start a layer of topsoil will be necessary for the project.




Also, since I haven't included pictures of the field in question yet, here's a few that I took a couple weeks ago.

Hau Chris,

My thought on mowing before broadforking was mostly for access.  Most of the area I'm looking at has around 3' of grass/brush growth, which, while encouraging to see, makes it difficult to put down soil amendments.  I've been thinking about picking up a scythe for the last few months for chop and drop purposes, perhaps this would be a good time to do so and save on fuel as well.

 With grass that tall a scythe would be not only less fuel but also faster cutting. One option would be to use a tractor and disk, this turns the whole plant under in one pass, if you had your amendments already spread, it would be a one time affair.
I do understand the spreading concerns but usually seed is the only thing you really need a low cut for application.

When you say use the fuel money to add some fungi to the soil, I'm not sure what you're referring to.  Mushroom compost?  Quick research on that does seem like it would be beneficial on my soil, being high in humus, chalk, and also more on the alkaline side, though it sounds like the real benefit is the residual fungi present.

Mushroom slurries are easy and not expensive to use and they can be applied at anytime. Mycorrhizae are best applied at time of planting (seed coating or tree root at planting). Mushroom compost is usually sterile because of Federal regulations that require heating it to 160 f temp. for 30 minutes.
Fungi can grow in pH levels as low as 4.0 and they will, through their enzyme use for nutrients, start adjusting the immediate area around them, these adjustments will be not only nutrients but also pH, water and oxygen.

Why would it be best to skip the lime and potassium at this point?  My soil test (hopefully attached this time), indicates a deficiency in potassium and a high acidity (~5.0 pH).  I'm assuming that the soil building steps I'm taking will have the more or less same positive effect, rendering these amendments unnecessary?

Unless you plan on planting a commercial crop now, these nutrients are already in that soil, they just aren't in the water soluble state, building your microorganism biosphere will be what does this for you, so if you made those additions then got the microbiome going, you just overdid those particular nutrients.
These are nutrients that can burn the roots of plants, so creating a situation of over availability can be damaging instead of helpful. Soil tests are designed for those who Dirt Farm not people with real soil that is bioactive and organism rich. By adding gypsum you are using a "time release" lime product instead of the product that only lasts one season or perhaps two seasons. If you use gypsum first then go back with lime, you can find that you over applied and slide the pH far to the basic side of the scale which can create a new set of problems for your microbiome and plants.  When you start to build soil, it is better to go slower than we always want, but it not only saves money to go slow, it also saves your microorganisms and the whole soil microbiome benefits as much as you the grower do.

Regarding the tilling, point well taken, I certainly don't want to kill the microbes I have there already.  My main concern was the large clods of clay that came up while broadforking.  The picture below isn't the best, but you can see that large chunks of clay were coming up 6" or so from the surface.  My thought was that the soil would build more quickly/evenly if the compost and/or chips were mixed in.  I suppose if I put down the wood chips/compost before broadforking, the surface could have been more even.  The area pictured here I scattered the cover crop mix on that I mentioned before, but nothing ended up growing.  I didn't use any amendments here outside gypsum, so I think compost to start a layer of topsoil will be necessary for the project.  

If you run a disk setup, and are turning in all your amendments in a single pass, add to the microbiome with compost teas, you will see clods begin to break down in under 30 days from application.
This is without any further additions, tilling, or any other manipulation. Those that till a fine seed bed are farming dirt, not soil, they do it because that is what has been taught as proper method since the late 1890's, around the same time period that chemistry started describing dirt as what we grow plants in.

Compost is always a good amendment and if you have good compost then you can make good compost teas and stretch that compost by using it both to brew teas and as a direct soil amendment. The two together are a powerful combination that can totally change a soil in just a few months, the longer you keep at this strategy the better the soil becomes.

Redhawk

Chris,

I'm in a pretty similar climate, with similar crappy deep clay soils, the tests are almost identical. My place was a christmas tree farm. I covered them in this thread on my attempt at soil improvement. Some observations in brief:

1) In the south, where the climate in the summer tends toward a savanna, my priority is to try to keep the fall/winter/spring forage alive through the heat. This will provide "armor" to prevent compaction and erosion the rest of the year. I think this is the lens to look at it. Without that protection, any progress will be short-lived. The soil life needs habitat, and that is job one.

2) I tried all manner of seed mixes in test plots. They all sucked. It was a waste of money. One exception was crimson clover, which I put down in the fall to provide spring biomass/nitrogen. That seemed to be helpful and is very cheap. I let it go to seed and it does come back- despite what the books say!

3) I tried all manner of amendments (see the thread). The only ones that seem to have made a difference were dolomitic lime (which is just a rock dust from limestone) and some local rock dust, which allowed for the clover to just go crazy- I planted white clover and the best clover out there is red clover, which I didn't plant. See point 2, waste of money.  I will be using the local rock dust from now on, the price point is just too low to bother with dolomitic. Yes, it is acidic (granite), but I co-apply with wood chips and the clover is doing great, which means at the root level everything is fine. My thread about the field conversion is a synopsis of what I have learned.

4) Bryant suggested that I consider amending and tilling initially, and I was too bull-headed to do it, since now I am a good permie /sarc. There is a field that was more compacted, with poorer growth than any other area, and I meticulously used minerals and tillage radish and let it grow high in the summer- and it still is way WAY behind the other areas. Take his advice if you have an area that there is no good soil life to disrupt, and do it all at once. This sounds challenging because you are basically guessing at what will be needed. I think his suggestion of the tilled gypsum, possibly with swales/keylining would have put me years and years ahead in that area. And ironically, it would have probably saved me some money. There are threads on here about using old gypsum wallboard, which could save some serious cash.

My new fields will get that treatment. What they will NOT get is tilled in chips. I did that in a garden area and it has been terrible for two years, even with crops of purely nitrogen-fixers. For two years!

I get huge amounts of chips, and the best thing I think they can do is compost in place and feed your little soil beasties. I do windrows for my silvopasture project, but in fields I think they are fine thinly spread on the surface. I use a manure spreader and put down a couple yards an acre, and repeat when it looks like the prior application is degraded. In spring that happened in 3-4 weeks, but over the summer they take a little longer in areas that are not deep in grass. The silvopasture field is still eating chips about every month, the soil is cool and moist since the grass is knee high.  

Which brings me to

5) Let stuff get high in the summer. This made so much sense when I saw Greg Judy's soil improvement crew. It hasn't rained here for weeks, and the soil in the deep grass is still damp and cool. That soil will hold life. That life will allow deeper rooting, and better infiltration. That infiltration will promote longer "spring conditions" for the all-season forage. That increased growing season will provide exudates to the beasties far into the winter, and they will be able to resume their duties earlier in the spring.

I made biochar, and it might be helpful, but the time involved was just not paying off. I made a total of three yards in that pit, which is a tiny amount in a field. Again, with a limited time budget, I have switched over to composting and compost tea per Bryant's advice. Most of my compost is being done in inoculated wood chip piles, and that is easiest for me. I'm using the biochar in the kitchen garden and in some new hugels.

Let me know if you ahve particular questions, hopefully there are some mistake I have made that can help you.

It’s been a year and wanted to post an update on progress.  First, some observations and reflections from the past year.

Getting a scythe has been a major help around the property in general, but I was kidding myself with scything that field.  By the time I got out there, the dogfennel was taller than I was, and I made it about 50’ over a few days and ended up injuring my shoulder trying to chop through the stuff.  Bought a bush blade after that, but wasn’t able to move nearly fast enough to get through it with the time I had available and the shortening days of autumn.  Working all day and scything at night and on weekends just wasn’t sustainable.  Ended up hiring a guy to bushhog it that fall.  Unfortunately, he came when the field was a bit wet and ended up with more ruts and compaction.  Joy.

I got a tractor over the winter so I could do the mowing myself and for other work around the property.

I continued reading through the winter and decided to follow Mollison’s described chisel plowing in a keyline plowing pattern.  The idea is to use a chisel plow or subsoiler to plow progressively deeper lines into the soil over time, minimizing overall soil disturbance, allowing plant roots to grow deeper and deeper, increasing water infiltration, and pulling organic matter deeper into the soil.  We have about 500’ deep clay before we hit bedrock, so I wanted to carve as deeply into that as I possibly could to assist future tree root growth.  There was a good amount of surface runoff from the soil as the main field is on a modest slope, and we get very dry in the summertime so it made sense to do this to store as much water as possible in the soil.  Doing this in a keyline system made sense as well as it would slow the water as much as possible and channel it to the ridges before it exited the property.

I opted for this strategy for a few reasons: money and time.  I decided not to use any soil amendments as I didn’t want to spend the money on them or the implements needed for spreading, and using the keyline plowing technique, I wasn’t sure how much they would penetrate into the soil anyway.  If anything, they would probably have washed down into the lines the subsoiler left and concentrated there.  Not something I wanted to deal with.  The subsoiler was surprisingly inexpensive - a single-tine plow that could go down 22” was under $200.

Keyline plowing was a fun experience and I learned a lot (i.e., made a lot of mistakes).  After marking the keyline and plowing above and below it, I realized that the lines themselves were getting quite off-contour.  The fields I plowed have some funny changes in elevation and quite a few obstacles that I think caused a lot of the lines I plowed to go too far off-contour.  I had to mark new keylines in areas where I felt that I wasn’t plowing in the right direction, and decided to just do the best that I could since I figured the lines cut would help with water infiltration regardless of whether or not they were perfectly following the keyline system.  Definitely a case where application and theory don’t quite match, and I met somewhere in the middle.

Since the fields had a lot of obstacles, I often had to stop plowing, negotiate the obstacle, and start again.  This quite often resulted in me driving over the top of lines that I had just plowed, recompacting them.  The compaction was not as bad as before it was plowed of course, but I cringed every time and it made for a bumpy ride.  I also ended up plowing myself into a corner quite often, or finding myself surrounded with areas that had been plowed, and needing to say the hell with it and just plowing some lines to get it done.  If you look closely in the pictures attached, you’ll see some interesting areas. 🙂

I couldn’t find any information on how close to make the plowed lines, so I opted to make them a tractor width apart.  This made spacing easy and I could simply roll the tires next to the previously plowed line.  This may have been a mistake - more on this later.

Plowing these fields took about 16 hours over two days (long weekend), and I was very proud of myself for doing all of the work quickly, right before a predicted week of rainstorms.  Anyone else in NC?  One thing I’ve learned since moving down here is that the only weather report you can trust is the one you give yourself when you’re standing outside.  No rain at all that week.  Hot and dry.  Since that time (Late July), we’ve had one significant rainstorm, which I’m not sure was a great test of the system since it was only a couple inches, but I didn’t see any runoff to speak of.  Needless to say, all the vegetation a foot to either side of the the plowed lines died.  The vegetation has come back somewhat, and the large lumps of earth that came up when the plow rolled through have settled some, but it’s still pretty lumpy.  I’ve mowed once since then (again, right before a rain that didn’t come), and I did it between the contour lines so as not to compact the plowed lines.  Will definitely be sharpening the mower blades this winter, but at least the really big clay clods got whacked into oblivion by the mower.

One thing I’m still trying to figure out is how to make my next pass with the plow.  At this point, I’m not going to do it until the spring to give the plowed lines more time to settle, but I’m not sure if I’m going to try to re-mark the key lines or just plow in between the previous plowed lines.  The massive oversight I made with making the lines so close together is that to plow between them, I’ll neatly drive right over the top of the previous lines, recompacting them.  I’m giving it until spring to allow time for roots to get down there when the plants finally get some water, and assume that the compaction that occurs when I plow again will be offset by the cracking of the hardpan and the organic matter that presumably made its way down there.

Enjoying reading about your progress!  Any updates?