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Will Hugelkultur beds prevent mineral and nutrient leaching?

 
Adam Moore
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I'm reading "The Intelligent Gardener" by Steve Solomon. He wrote about mineral leaching in excessive rainfall states. This last month in Ohio it seemed like it almost rained everyday for the last month. I have never seen this much rain. Lots of flooding in our city just a couple of weeks ago. Now that we finally dried out, I was wondering if the wood in the Hugel beds would not just absorb and store the water from big rains but also store the water soluable nutriets and minerals that those big rains are washing down through the soil? If so, can the microbs and roots reach back into the wood to pull the mineral/nutrients out. Or do they have to wait till the wood rots to release what it absorbed?
 
John Elliott
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Think of leaching as a continual process that continues up until the substance is exhausted. Like reusing tea bags. Some people save a tea bag and use it to brew a second cup. Less tea flavor and caffeine is going to be present in the second cup though. Or the third cup. By the sixth cup, I doubt there would be much tea flavor left. Even if you let it soak all day.

But tea leaves are all crushed up and have lots of surface area, so it is easy to extract the minerals and nutrients. A big log in a hugelkultur bed is another story. It's probably going to take years for all those nutrients and minerals to leach out, even if there was three weeks of pretty constant rain. Since the buried log was already saturated with water, it probably didn't pick up any nutrient laden water from upstream, but you never know. If there was a septic tank field or some fertilizer runoff from uphill, and it flowed through the hugel, all that wood with all its surface area could pick some nutrients up by adsorption/absorption and let the water pass. There is a lot of interesting science in the flow of nutrients and it takes a lot of study to begin to understand how it works.
 
Adam Moore
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Thanks for the reply John. So I wonder, if there is enough wood in the Hugel bed that maybe it could absorb enough water (assuming the wood is not already saturated) to keep the surounding soil from saturating with water. Maybe this might help a bit to lesson the nutrients and minerals from being washed down to the subsoil? From my understanding the heavy rains cause more leaching than a light rain. Maybe the Hugle beds can moderate the effect of heavy rains a bit?
 
Dale Hodgins
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I'm in a wet climate and have taken some steps to preserve nutrient by concentrating rich soil amendments at the top of fairly tall beds. I figure that winter rain will wash through several feet of nutrient poor woody materials and those materials will absorb some, hopefully most of it.

Nutrient is more likely to travel when freshly applied. If it has already spent months mixed with the soil, much of it will be absorbed by the less rich material.

I discoverd key hole gardening a few weeks back and it turns out that my approach to nutrient delivery is similar. There's a plan to incorporate a few tons of manure next spring after the rain subsides. The excavator will cut trenches a couple feet deep where manure will be dumped to cap the piles. The greediest plants will go close to it. There is generally no rain for 3+ months and total saturation is likely to occur in December. That's 7 months of growing and composting before any leaching is likely.
 
Landon Sunrich
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So I'm slamming my head over not being able to figure out how to get pictures up / adding potassium (in the form of wood ash and bio char) to my bed when apparently that can be an issue with wood core beds - but I am keeping up on the discussion here. I am looking forward to checking out (literally. from a library) 'The Intelligent Gardener'. Cation Exchange is a concept I am familiar with - but still don't completely understand. Anyway...

My assumption has always been that the wood core filled with split exposed grain wood - in my case the addition of wood chips - would slow and 'catch' minerals being leached. Especially those being added in the form of a soil amendment. Like, if I put on a good dose of blood meal onto loose sand on top of clay, water is going to sweep all of those minerals away - but if there is something for it to soak into - like wood - it should be more or less bound there until accessed by a plant, fungus, whatever. I mean a Huglekulture or any other wood based bed is going to be fairly thick. Mine is at least 3 feet think - so that water has quite a bit of organic mater to work through before it finds a way to run out of the system. I think wood chips are key here though too - I mean it provides a whole lot of surface area and water -saturated with whatever it picks up - is going to be caught and trapped by it.

Is my thinking wrong here?
 
John Elliott
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If it makes you feel better, leaching is a concept that is more applicable to chemical fertilizers, rather than biological fertilizers like manure, rotted wood, chop&drop, and mulches. Remember the big difference between these fertilizers and wood ashes, urine, ammonium phosphate or nitrate is that the latter ones do not have cell walls holding them in place. They dissolve and can be carried away by the water that flows by. If you pee on your hugelbed in a thunderstorm, you can watch it flow until it hits some sort of impound and that's where your nutrients will be. Solid pieces of biological material, unless the rain is strong enough to float stuff away, is not going anywhere. The phosphorous and potassium in that stick or piece of mulch is there, ready to nourish roots or fungal hyphae that happen to be around when the cell wall gets broken down (by a variety of microbial processes).

OK, that explains the P and K parts, what about the N? Nitrogen is much more labile, since it can convert to ammonium forms (volatile) and nitrate forms (highly soluble). The way that nitrogen gets recycled and remains in your soil is through soil fauna. The thousands millions of sowbugs, nematodes, collembollans, worms, beetles, and arthropods that eat and excrete. If you have a lot of buried wood, with critters eating the buried wood, they are providing frass (excreta) on a daily basis to the roots that are all around. So if a heavy rain washes through the soil and carries off yesterday's frass, it quickly gets replaced by more microfauna activity. They chew big pieces of biological fertilizer and excrete it as smaller pieces of biofertilizer.

Next time you start to worry about whether or not your hugelbed is leaching out nutrients, think about your friend the bess beetle. As long as there is wood to be chewed up, they will be chomping on it, turning it from biomass taking up space into biofertilizer.



Thanks, Bess.

 
Dale Hodgins
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John Elliott wrote:If it makes you feel better, leaching is a concept that is more applicable to chemical fertilizers, rather than biological fertilizers like manure, rotted wood, chop&drop, and mulches. Remember the big difference between these fertilizers and wood ashes, urine, ammonium phosphate or nitrate is that the latter ones do not have cell walls holding them in place. They dissolve and can be carried away by the water that flows by. If you pee on your hugelbed in a thunderstorm, you can watch it flow until it hits some sort of impound and that's where your nutrients will be. Solid pieces of biological material, unless the rain is strong enough to float stuff away, is not going anywhere. The phosphorous and potassium in that stick or piece of mulch is there, ready to nourish roots or fungal hyphae that happen to be around when the cell wall gets broken down (by a variety of microbial processes).

OK, that explains the P and K parts, what about the N? Nitrogen is much more labile, since it can convert to ammonium forms (volatile) and nitrate forms (highly soluble). The way that nitrogen gets recycled and remains in your soil is through soil fauna. The thousands millions of sowbugs, nematodes, collembollans, worms, beetles, and arthropods that eat and excrete. If you have a lot of buried wood, with critters eating the buried wood, they are providing frass (excreta) on a daily basis to the roots that are all around. So if a heavy rain washes through the soil and carries off yesterday's frass, it quickly gets replaced by more microfauna activity. They chew big pieces of biological fertilizer and excrete it as smaller pieces of biofertilizer.

Next time you start to worry about whether or not your hugelbed is leaching out nutrients, think about your friend the bess beetle. As long as there is wood to be chewed up, they will be chomping on it, turning it from biomass taking up space into biofertilizer.



Thanks, Bess.



I've seen a few of John Elliot's posts and he seems to be some sort of soil scientist. John, I see you joined the forum recently. Were you recruited for your expertise on these matters. Your title of "pollinator" is the first I've seen with that distinction. I'm going to defer to John whenever a soil chemistry thing comes up. --- John, You might want to do one of those introductions threads although I fear you may create quite a bit of work for yourself. We will pepper you with questions. Thanks: Dale
 
Joan Perez
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Landon Sunrich wrote:So I'm slamming my head over not being able to figure out how to get pictures up / adding potassium (in the form of wood ash and bio char) to my bed when apparently that can be an issue with wood core beds - but I am keeping up on the discussion here. I am looking forward to checking out (literally. from a library) 'The Intelligent Gardener'. Cation Exchange is a concept I am familiar with - but still don't completely understand. Anyway...

My assumption has always been that the wood core filled with split exposed grain wood - in my case the addition of wood chips - would slow and 'catch' minerals being leached. Especially those being added in the form of a soil amendment. Like, if I put on a good dose of blood meal onto loose sand on top of clay, water is going to sweep all of those minerals away - but if there is something for it to soak into - like wood - it should be more or less bound there until accessed by a plant, fungus, whatever. I mean a Huglekulture or any other wood based bed is going to be fairly thick. Mine is at least 3 feet think - so that water has quite a bit of organic mater to work through before it finds a way to run out of the system. I think wood chips are key here though too - I mean it provides a whole lot of surface area and water -saturated with whatever it picks up - is going to be caught and trapped by it.

Is my thinking wrong here?


I think that biochar will not increase a lot the potassium content of the soil. The beauty of the biochar is that thanks to its structure, will increase the cation exchange capacity of the soil, preventing the leaching of those precious minerals and it will be at the same time a good habitat for the beneficial funghi, bacteria and microorganisms.
 
Matu Collins
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Another great thing about all those bugs besides their frass is that they are little bags of fertilizer when they die and rot or get eaten...
 
Dale Hodgins
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Matu Collins wrote:Another great thing about all those bugs besides their frass is that they are little bags of fertilizer when they die and rot or get eaten...


My thoughts exactly. Then there's the millions of little nests, pupae cases, shed skins ... Any bugs that tunnel into the wood are creating pathways for root and water penetration. I wonder if there are any bugs that would make their home in the beds but forage over a wider area. This would tend to bring nutrient into the system just as chickens will enrich the soil around their coop.
 
Matu Collins
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Worms and ants, at least. Definitely ants

A snake shed its skin on one of mine a couple of weeks ago! I'm sure the microclimates and the rocks and broken pottery were factors but I couldn't help but think maybe the snake has overheard us talking about the hugelkultur idea and is contributing what he has to offer...
 
John Elliott
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Dale Hodgins wrote:
I've seen a few of John Elliot's posts and he seems to be some sort of soil scientist. John, I see you joined the forum recently. Were you recruited for your expertise on these matters. Your title of "pollinator" is the first I've seen with that distinction. I'm going to defer to John whenever a soil chemistry thing comes up. --- John, You might want to do one of those introductions threads although I fear you may create quite a bit of work for yourself. We will pepper you with questions. Thanks: Dale


Thanks, Dale. I'm a retired research chemist. During my career, I didn't deal at all with soils, but it has been an interest I have picked up since I have more time to garden. When I figure out the proper forum to post it in, I'll let y'all in on my method to turn alkaline batteries into micronutrient fertilizer. One man's trash is another man's treasure.
 
Susan Noyes
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John Elliott wrote:

Thanks, Dale. I'm a retired research chemist. During my career, I didn't deal at all with soils, but it has been an interest I have picked up since I have more time to garden. When I figure out the proper forum to post it in, I'll let y'all in on my method to turn alkaline batteries into micronutrient fertilizer. One man's trash is another man's treasure.


WOW! I look forward to learning about turning batteries into fertilizer!
 
John Elliott
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Susan Noyes wrote: WOW! I look forward to learning about turning batteries into fertilizer!


You can find it here in the composting forum.
 
Paulo Bessa
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I wonder how many of you have actually tested for the nutrients in Hugelkultur?

I used a NPK test kit and I have tested a hugelkultur versus a normal bed (native soil is clay, wood used was poplar), and after a 3 month growing season with plenty of rain nearly day, the conventional bed had nitrogen levels medium to low, A raised bed (no hugelkultur) with thick mulch, had strong nitrogen levels. Hugelkultur with thich mulch had similar strong nitrogen levels, while hugelkultur beds without mulch, had low nitrogen levels. All places were all treated similarly in the start of the growing season, with plenty of compost added.

This for me suggests that hugelkultur beds are no different than any other raised beds in reducing nitrogen leaching, which is the most easily leached nutrient. At least i haven't seen a difference yet.

It seems that it's the mulch (or vegetation cover) that does the job of preventing nutrient leaching, namely nitrogen. I also have seen a relationship between nitrogen levels and how long beds were naked and exposed to rainfall.

Furthermore, I tested beds covered with normal crops and with nitrogen fixing species: nitrogen levels were higher when nitrogen fixing species are used.

My conclusion so far: any exposed soil and continuous rainfall and no matter your source of nitrogen (organic or chemical, or whether hugelkultur is used), you will have always leaching of nitrogen, and if the rainfall is enough, you will end up with low levels.

In a nutshell, always cover your soil, and always use nitrogen fixing species.

But don't get me wrong: I am a fan of hugelkultur - crops grow better and I guess it is mostly to do with increased soil life, better soil structure and optimal moisture. I also completely agree with John, the wood in hugelkultur could provide a more sustained pool of nutrients to replenish the leached ones, however so far I have not seen a positive effect in nitrogen levels in my soil tests.

I must repeat these experiments later in summer and outside of the growing season and see if I can find a difference for the hugelkultur beds.
 
John Elliott
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Paulo Bessa wrote:I wonder how many of you have actually tested for the nutrients in Hugelkultur?

I used a NPK test kit and I have tested a hugelkultur versus a normal bed (native soil is clay, wood used was poplar), and after a 3 month growing season with plenty of rain nearly day, the conventional bed had nitrogen levels medium to low, A raised bed (no hugelkultur) with thick mulch, had strong nitrogen levels. Hugelkultur with thich mulch had similar strong nitrogen levels, while hugelkultur beds without mulch, had low nitrogen levels. All places were all treated similarly in the start of the growing season, with plenty of compost added.

This for me suggests that hugelkultur beds are no different than any other raised beds in reducing nitrogen leaching, which is the most easily leached nutrient. At least i haven't seen a difference yet.

It seems that it's the mulch (or vegetation cover) that does the job of preventing nutrient leaching, namely nitrogen. I also have seen a relationship between nitrogen levels and how long beds were naked and exposed to rainfall.


Very interesting observation Paulo. There is a competing explanation I can think of though. Nitrogen leaches at the same rate whether the hugelkultur is mulched or not, but when there is a heavy layer of mulch on top, there is a lot more soil food web there, and all the soil critters use it to immediately replace the nitrogen that was just leached. When the hugelkultur is not mulched, well then you have to rely on plant roots getting down to a rich piece of rotted wood to find their nitrogen.

I made a big mistake when I built my hugelkultur beds this last winter. I topped them with 2" of dirt, with the idea that in the spring, seeds would sprout and quickly grow to cover the hugel with a canopy and it would be self-mulching. I'm not very happy with how that plan turned out. I swear it's taking longer for the canopy to fill in than it did with my old, conventional method of gardening. For my fall plantings, I'm going to learn from your experience and top the hugelkultur bed with a thick mulch and plant or transplant into that.
 
Paulo Bessa
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John Elliott wrote:
Very interesting observation Paulo. There is a competing explanation I can think of though. Nitrogen leaches at the same rate whether the hugelkultur is mulched or not, but when there is a heavy layer of mulch on top, there is a lot more soil food web there, and all the soil critters use it to immediately replace the nitrogen that was just leached. When the hugelkultur is not mulched, well then you have to rely on plant roots getting down to a rich piece of rotted wood to find their nitrogen.

I made a big mistake when I built my hugelkultur beds this last winter. I topped them with 2" of dirt, with the idea that in the spring, seeds would sprout and quickly grow to cover the hugel with a canopy and it would be self-mulching. I'm not very happy with how that plan turned out. I swear it's taking longer for the canopy to fill in than it did with my old, conventional method of gardening. For my fall plantings, I'm going to learn from your experience and top the hugelkultur bed with a thick mulch and plant or transplant into that.


Great to talk to you John. In a way its exciting to talk to someone with background in chemistry.

I agree with you that probably the nitrogen, as soluble as it is, it will leach freely, but in mulched beds it will be replenished both by the thriving life under the mulch and also by the decomposing mulch releasing nitrogen (also done by the microorganisms).

I had this big trouble with nitrogen leaching as I realized because this summer i had something like at least 80 days of rain in my 90 day growing season. I proceeded then to test the nitrogen levels and mulching was one of the the conclusions I got to keep nitrogen levels, the other was to use stuff like broad beans and peas, since I measured higher nitrogen there.

However, mulch also messes with my plans, because I want to rely in self-sowing vegetables and the seeds will not germinate in such thick mulch. The other challenge is to find a permanent ground cover, something that I could grow over the winter, survive the winter but be only an annual, so that next year i could plant brassicas, carrots, squash in those spots. I though about covering everything with plastic to prevent the leaching of nitrogen, but then I am afraid of making a mistake by starving the microorganisms of light, water and air.

Ideally i could have a self-mulching crop around, these would be the invasive lupins growing all around Iceland. But they are very agressive and a perennial, and with time they will shade and grow over any other plant. So I just walk a few meters and chop them to cover the ground.

Interestingly, I had another observation John. I saw a small decrease in potassium in the hugelkultur beds compared to the other beds. I did not had many hugelkultur beds so this could be an artifact or random variation. Anyways I was expecting to find the opposite: more potassium there.







You spoke

 
Paulo Bessa
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Joan Perez wrote:
I think that biochar will not increase a lot the potassium content of the soil. The beauty of the biochar is that thanks to its structure, will increase the cation exchange capacity of the soil, preventing the leaching of those precious minerals and it will be at the same time a good habitat for the beneficial funghi, bacteria and microorganisms.


I have never tried biochar but i found interesting also to experiment with the notion of changes and increased or decreased nutrient availability.

I also noticed that the pH of hugelkultur beds seems to be always slightly lower than conventional beds, but this is produced probably by increased microbiology life and decomposition.
pH of native clayish soil 7.3 (even though Iceland has many acidic soils, its rock material is mostly alkaline
pH of conventional beds 6.5
pH of hugelkultur beds 6.3
 
Ken Peavey
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There is science behind hugelkulture.

As part of my ongoing leaf mold study, I've been looking at lignin.
Lignin is that substance which gives trees their strength. Hugelkulture puts a massive amount of lignin into the soil where it breaks down slowly. Lignin decomposes into humus, which serves to increase the cation exchange capacity of the soil. In addition to retaining moisture, the humus grabs onto nutrients and minerals, keeping them available for plants to use easily.

What also needs to happen is the decay of the cellulose and hemicellulose in the cells to get that out of the way in order for the fungi to become dominant. Bacteria will decompose the cellulose, but do not produce the enzymes which will decompose lignin. That's the job of the fungi. The initial bacterial decomposition can take a few months, after which the level of humus would slowly increase. The humus would not completely prevent mineral and nutrient leaching, but I think it would surely hold on to much of it. Once the lignin has broken down to humus, the resulting organic matter is stable, staying in the soil for decades to centuries.
 
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