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
thousandsmillions 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.
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?
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...
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
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.
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.
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.
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.