The urban myth about woodchips and nitrogen

  All over the Internet ,when you go looking for information about using wood or wood chips in gardening, you read about how certain items will suck nitrogen out of the soil.
When you start looking for factual evidence though, it seems very hard to find any scientific study that backs this up.
Why is that?

     Wood, when it comes in contact with soil, activates mechanisms in certain bacteria which then consume nitrogen as food so they can decompose the wood.
If this wood is sitting on top of the soil (fallen tree, dropped tree branch and so on) then these mighty bacteria will become active, but only to a depth of around 5mm.
This means that the answer to the nitrogen "robbing" wood is only involved in a minute area under and around the piece of wood.
Bury that piece of wood and you will be able to measure nitrogen depletion about 10mm from the wood (in all directions since the wood is under the soil).
This brings the "nitrogen loss" caused by wood into the magical realm of "Urban Myth" since such quantities of nitrogen  are small (minute really) when put into proper comparison.
This can be shown simply by looking at the soil in a forest floor, dead wood fall, leaves, dead undergrowth are all present and yet new growth is always present, even next to dead wood you will find nitrogen needy ferns growing.
If the myth about wood was true, these plants should not be there, or at least not thriving as they do.

     Most of us use wood chips for paths and mulching around trees, areas where the small amounts of nitrogen being used by the bacteria are truly negligible in significance to the growth rate of the plants near by.
Keep in mind that this is because in nature, almost all the available N is in compound forms and slow release is the norm.

    Trees feeder roots are normally located from half the distance from the trunk out to the outer edge of the canopy drip line (some species go out past this drip line further than others).
What does this mean to us as growers?
It means we don't have to worry so much about nitrogen loss when it comes to bushes and trees, unless we want to cover an area from the magical 6" diameter away from the trunk all the way out, 3 or 4 feet past the outer edge of the canopy drip line.
Tree roots (the feeder ones we are most interested in) live from half the distance trunk to drip line out to around 3 or 4 feet past the drip line.
These "important" (and they really are) roots are found at a point of 1-2 cm below the soil surface down to around 30-40 cm deep.
The holding roots (tap root and large spreading main roots) go deeper since their job is to hold the tree in place under the stresses of wind events.
How deep these roots penetrate is dependent on how far down bed rock is found.
That is why my state (Arkansas) has such a large number of downed trees in heavy storm events, the bed rock is close to the soil surface, no deep roots means the trees aren't well anchored.
On my farm we are lucky, there is up to five feet of soil depth and the bedrock is highly fractured, so tree roots can anchor really well (and these roots keep adding to the fracturing of the bedrock).

   The gardens, where we should be worried about nitrogen being bound up by wood (especially chips) are the perennial and annual vegetable and herb gardens.
These plants don't have roots (for the most part) that go deep and widely spread, usually their roots are very near the surface and within a 1 meter diameter circle from the main stem.
Squash and other vining plants put roots out all along their vine leaf nodes, but these are still shallow roots, so they are vulnerable to nitrogen binding by any wood chip mulch we might put down.

Nitrogen, the kinds we plant growers are most interested in, as I mentioned earlier, is a slow release nutrient when provided in natural forms.
For faster access to plant roots, synthetic forms are needed, Not What We Want To Hear!

Natural Nitrogen comes to plants in large chain molecules.
Nitrites, Nitrates, Ammonia salts are the normal, natural forms we can put into soils via composts, manures, urine and teas made from mixtures of these along with greenery.
Compost is a very long term additive, it actually takes five years for it to give up all the soil and plant goodness it contains.
Which makes it very much an ideal additive in gardens.

Now that you know more about nitrogen forms found in nature, it should be easier to go about using woodchips for a mulch.
They really don't cause any problems by "robbing Nitrogen" from your plants, especially if you use compost around or over them.
The nitrogen from the compost will leach through those wood chips and still find the soil beneath your mulch chips.
If you build a hugel and use greens and or compost as part of your filler ,then most likely you have made up for any Nitrogen loss that buried wood might cause.
If you top dress with compost or do a chop and drop of cover crops, like most people do, then you have added more slow release nitrogen than the wood might take up.
Mother Nature loves to use wood to build soil, so there really isn't any reason we should not follow her lead and do the same.
We just don't need beavers to make woodchips out of trees like she does.

Redhawk

Outstanding.  Fantastic post.

If one were to rototill a thick layer of chips into the soil, which I have done, yes, then you would see some signs of nitrogen deficiency for a season.  But at the same time, you would note a spike in microbial and fungal activity a year later, which would more than off-set the one-year loss of N.  And functionally, that N wouldn't be lost -- it would be tied up.  But a year later, that N would be fed to your plant roots by those same microbes and fungi that were attracted to the buried bio-mass.

Throughout the soil profile, different bacterial microbes are at work.  Some can stand the heat and irradiation from the sun that is found on the soil surface.  Just below the surface, or below the mulch layer, you'll find other microbes that thrive in those conditions.  2 inches down, 4 inches down, 6 inches down . . . different microbial communities will predominate.  In the same way that in an active compost pile, you'll find different microbes active throughout the profile (some like it hot in excess of 130 or 140 degrees, some like it between 120 - 130, some cooler . . .), you have to recognize that microbes differ in the way they respond to various carbon sources.  The lignin and cellulose found in wood chips are complex organic polymers.  It takes a variety of microbes to break these down, and at different stages of decomposition, different microbes will thrive.  So, were you to plow under a layer of wood-chips, those microbes best suited for that stage of decomposition will multiply rapidly.  But here's the point: eventually, and quite quickly, those microbes best suited to "carry" (or more accurately, assist in the transfer of) N and other nutrients to the plant roots will begin to multiply.

It's not like the plant is neutral in all this.  Plants are tremendously complex.  They test what is in the soil, and they exude chemical invitations (root exudates) that send a message to the kinds of microbes that they desire to work with.  The plant pumps out these exudates filled with sugars to feed the correct microbes, even as those microbes are breaking down the bio-mass/wood chips.  Thus, if there is a big piece of wood in the soil next to the roots where the plant is growing, the plant will work with that chunk of wood, not against it.  Yes, for a time the N in the immediate area will be bound-up, as you said above in your post.  But only temporarily, and in the long run, those plant roots will find a way to encourage the microbes to bring that N over and feed it to the plant.  Fungi are tremendously effective in doing this, as they crave the sugars that the found in the root exudates.  The conversation would be something like, "I'll break this carbon down for you, in exchange for pie", says the fungi.  Tree responds, "Sounds like we've got a deal."

Speaking of pie, if I had a spare piece laying around, I'd award your post with a slice.  Given the fact that it IS virtual pie, and that my offer of virtual pie is imaginary, I hereby offer you virtual virtual pie.  Enjoy.

And no, I don't regularly till chips under.  I don't have to.  The earthworms are doing the heavy lifting in that regard, integrating the carbon down into the soil profile, but not before they have treated the carbon to a chemical and biological bath of their own digestive enzymes and gut microbes.  With a new 6 to 12 inch layer of wood chips added annually, the decomposition and integration of that carbon is happening throughout the year.  Having done this now for over 10 years, I've got the richest soil in town.  And the fattest earthworms.  And the happiest microbes.

hau Marco.  Soil is so complex that we are just now beginning to really understand it.  In the woodchip realm, microbes arrive first and as they chug along mycelium arrive to give a helping hand.  
Soil is chock full of symbiotic relationships, most of which we don't currently have a clue about, but we are gaining ground at understanding soil.
Different microbes are found from the surface all the way down to 24 inches in areas with friable soil to that depth.
The underlying clay layer (found over most of the Northern continent) seems to be the limiting factor in soil life. Once you probe past the first 5 inches of that clay layer you find little microbial life that deals with our main interests.
At that point the microbes seem to switch to minerals much more than organics as their food source. This too is very important but that mineral mining can't be used by our plants unless the mycelium are attached to the roots to make those minerals available to the plants.

As I said, soil is so complex that we are just getting to where we can see the picture mother earth has been using for billions of years.

I have built a lot of beds by digging out the bed and filling it back in with fall leaves mixed with the original soil.
They never did well at first until I learned about the potential for nitrogen depletion.
Now I add in greens as well as the leaves,and plant legumes for a season.
All of the beds are now rich,moist and delicious.
They hold water great and I plant in them by plunging my hands in and working them back and forth, no shovels.
My little orchard is covered in woodlands and fall leaves.
I even dug some of this carbon into the planting holes,figuring that water retention was as least as important as nitrogen to a new tree.
Besides, pee is easily applied later,especially if there is something to soak it up.
I have even considered purposefully tilling chips into my soil,with the idea that tying up the nitrogen it might give newly planted clover the advantage.

A forest floor has all the nitrogen a plant needs because it contains a mixture of decomposing organic matter, microorganisms and fauna that shuttle it about. Trees and other plants are also continually shedding plant litter over their life times whereas they only add stem wood once. If that forest floor was covered in stem wood chips alone the story would be completely different, have a look at the chart below. Without years of leaves, branches and bark the microorganisms that break down the stem wood have to draw that nitrogen from somewhere, about 7 g per kg if you want the equivalent of a forest floor. Lower rates of N aren't the only issue, phosphorus is also 5-6 times lower in aged stem wood. Adding aged stem wood chips alone will make soil deficient in many nutrients and potentially add diseases. Have a listen to a story by Hendrikus Schraven:
https://youtu.be/LjyT1UeYuzo?t=335

Craig Overend wrote: Trees and other plants are also continually shedding plant litter over their life times whereas they only add stem wood once.

I don't quite agree with that; our trees shed branches of different sizes at various times due to breakage.  And regarding wood chips being stem wood, I see most people advocating using wood chips which include the entire branch including leaves.

This is a great topic -- simply noting that tying up nitrogen is at most temporary rather than permanent is huge.

Interestingly, Sharifi et al. 2014 found that in their experiment mixing wood chip bedding in with manure actually increased the availability of nitrogen to crops over the course of eight years.

Experimental research depends on a lot of factors, of course. According to another study by Hornyak et al., (2010), "wood-chip application can potentially immobilize between 19 and 38 kg N ha −1 in the first year after harvesting." In their context, they were seeking to slow down dispersal of nitrogen into the environment. Miller et al. 2013 found that wood chips slowed the leaching of nitrogen from fresh manure over years. But it seems like that doesn't counteract the benefits for crops of adding wood chips.

(If anyone is interested in reading these, PM me and I can send you full references.)

That is an important point, Chip.

Nitrogen gasses-off if it doesn't have something to grab onto.  That's why green grass clippings will heat-up your compost pile, but if you let them dry out and turn brown, all that lovely N has gassed off and returned to the atmosphere from which it came.  In this way, wood chips become a nitrogen sink that hold the element until it can up absorbed within the local ecosystem.  

Has anyone watched Joel Salatin's video about how they compost animal carcasses?  They butcher a lot of chickens, rabbits, pigs and cattle.  That's a lot of blood, guts and bones.  He spoke about a time where someone left a gate open and a train hit a bunch of his cattle.  What they do it bury the animals and guts and such in wood-chips.  They re-use the chips after about 9 months -- everything has decomposed by then.  After two cycles, they load the heavily decomposed chips into a manure spreader and spread them onto the fields.  All that N that was in the animal carcass and waste is captured by the wood chips and then transferred to the field.  Without the wood chips, it would stink, attract flies and vermin, and would just gas off all that nitrogen.

Additionally, the wood chip medium becomes the "reef" to hold all the microbial life.  Just as important as capturing the N is growing the massive volume of microbes.  More microbes = more N.  They cycle feeds itself and gets richer with time.

If you haven't seen his system, it's worth watching.  He's funny and it's such a simple and elegant way of dealing with all the animal guts, I think it's brilliant.

It is actually very easy to overcome nitrogen problem, even when the wood  chips are dug in into the soil. As a matter of fact, I experimented with potted plants, where I planted one in regular potting soil and one into regular with about a third of wood chips soaked in undiluted urine (for nitrogen) with several types of plants. They are all doing good, however I did add a few times more urine (this time diluted) -every two weeks or so, but more is good too. No yellowing, even with a third of it and even in the pots. And now those pots hold moisture very well, and are better aerated. I do not like digging good soil, but if soil is very poor, digging in wood chips/twigs/leaves with manure, urine or other high nitrogen material at first probably is a good idea. Of course, I would watch plants for first two months, and at any sign of deficiency just give them more. In two months there would be just benefits.

Joy Oasis wrote:It is actually very easy to overcome nitrogen problem, even when the wood  chips are dug in into the soil. As a matter of fact, I experimented with potted plants, where I planted one in regular potting soil and one into regular with about a third of wood chips soaked in undiluted urine (for nitrogen) with several types of plants. They are all doing good, however I did add a few times more urine (this time diluted) -every two weeks or so, but more is good too. No yellowing, even with a third of it and even in the pots. And now those pots hold moisture very well, and are better aerated. I do not like digging good soil, but if soil is very poor, digging in wood chips/twigs/leaves with manure, urine or other high nitrogen material at first probably is a good idea. Of course, I would watch plants for first two months, and at any sign of deficiency just give them more. In two months there would be just benefits.

Not taking the urine...
Be very careful when  using any urine diluted or not human or animal ..don't get it on any fruits or veg that you won't cook before eating   , especially soft fruit such as strawberries . The reason being is that urine whilst sterile at the outlet quickly becomes an e-Coli  propagator .

  A further note about wood chippings :-

The area involved was 30 yards x 12 yards ( two traditional English garden allotments )   if  they are green & reasonably fresh wood chips  they break down a lot quicker that dried out ones , especially if they have been deep tilled into a wet gray / blue y clay in the vain hope of a quick improvement into crumbing the clay .

For   I happened to be given about three tons of old dry chippings that I had to sweep up off a concrete barn floor . Added to those dried wood chips was five tons of 20 year old well composted stable muck including the straw beddings  &  two tons of cattle muck that had originated from cattle being overwintered on four foot deep straw bed .
( Old British way of keeping 30 or so cattle in winter ...called keeping the cattle in a , " Crew yard " part of it was open to the elements ..  Each day a few loads of clean wheat straw was forked over the cattle crew yard floor whilst the cattle were in the enclosed area ,  come spring it was about four feet deep , well soaked in dung , urine & rain )  .
I tilled it all deep down to 24 inches ,  a good half dozen times in the initial tilling when I took the gardens on  . Water would come out the clay and lay in the rows I'd just done.. Later on I  found out that the area had a very slight natural spring in it , in winter it was quite a flow .

It took three years & another  two major rototill sessions  of me  adding several more tons of composted manures including  straw beddings in the second year over all that ground of mine  .  By the time the third year arrived  the gardens started to show a big improvement.

You could have grown truthfulness  & honesty  on a politician in that third year it was so fertile . I then started a five bed five year rotation system of crops including leaving one bed fallow in the  fifth year.

It worked well for us for almost 20 years before  we sold up & moved on to a smaller set up in readiness for our old age and my disabilities getting worse .

I did not have experience with dried out chips, just with fresh ones. In our area tree trimming companies deliver the chips with leaves and twigs for free, but one has to take full truck load. I got it from people who got them this way, and they were fresh, Actually they were getting hot sitting in their driveway and were steaming. Maybe dried ones do not work the same way.
I think you are mixing urine with manure. Urine doesn't carry e coli. And since I use our urine and we are healthy, I do not worry about it at all. I am sure, our garden gets wild animal/bird urine and manure all the time. Soil organisms work those through. Of course, I wouldn't pour urine over lettuce, that I will be eating soon, but more from cultural ick factor than for any real danger reason.

 Getting animal manure, grass, hay and straw from unknown sources is becoming bigger problem now, because in 2007 herbicide companies released herbicides, that stay in the soil for many years, so any of those now can contain those and any compost made from it will be a killer compost. That's why many people now grow their own compost materials or use wood chips instead.

I've used sawdust as potting soil for decades. Ideally mixed with elm or ash leaves, but by itself if that's what I could get. Sometimes I've added ammonia, sometimes not. After a couple years it breaks down into good dirt. Grew an elm tree 30 feet tall in a barrel of straight sawdust. I just dragged home some tired sawdust to mix into the too-sandy front garden to make it hold water better. When I dig the grass out of the raised garden, that'll get replaced with more sawdust. Nitrogen is easy to add if you need it.

I've used woodchips of various types with annual vegetables for a number of years now. First application is usually about 10cm (4") thick. Most of the time, and certainly after the first year, all is good. These days, I put down a green manure which includes legumes before I top up with chips. Top ups are usually less than 10cm thick. I try to have living roots in the soil as much as possible and I never walk on or dig beds (unless I'm harvesting a root crop). I'm very happy with what happens to the soil over time but of course I can't ascribe the improvements to any one thing. It's no doubt all three - mulch, living roots and no soil disturbance.

Various studies that may touch on the subject:
http://link.springer.com/article/10.1023%2FA%3A1005978101429

Another article:
http://compost.css.cornell.edu/calc/lignin.html

Rez Zircon wrote:Various studies that may touch on the subject:
http://link.springer.com/article/10.1023%2FA%3A1005978101429

Another article:
http://compost.css.cornell.edu/calc/lignin.html

Thanks REZ that kind of nails things down about nitrogen & decomposition for any one who cares to read & understand it .

I picked up my version of things from the Cornell University extension unit .

Size matters:

Consider a block of wood 1 foot cubed.  It has 6 square feet of area.  That's the area where the bacteria and the wood interact.  

Cut it in half each way, so you have 8 6" cubes.  Each 6 foot cube has 6  1/4 square foot faces so you have 8 * 1.5 = 12 square feet.  Half the size chunks, double the area.

Go down to 1 inch cubes and we have 1728 * 6 * 1/144.  (1728 cubic inches in a cubic foot.  1 inch is 1/12 of a foot, so each face is 1/12 x 1/12 = 1/144 square foot.

Suppose we use sawdust from sanding furniture.  Sawdust is typically about 1/10 of the size of the grit:  100 grit paper produces sawdust 1/1000 of an inch in diameter.  A cubic foot of wood turned to sawdust has about 12,000 square feet of area.

Use all the wood chips you want.  If you use fine sawdust, mix it with hot manure for a few weeks.

David Gould wrote:
Be very careful when  using any urine diluted or not human or animal ..don't get it on any fruits or veg that you won't cook before eating   , especially soft fruit such as strawberries . The reason being is that urine whilst sterile at the outlet quickly becomes an e-Coli  propagator .

As E. coli isn't present in healthy urine, I wonder how it would get into the urine that is put on plants?  It seems a very low risk.

Tyler Ludens wrote:

David Gould wrote:
Be very careful when  using any urine diluted or not human or animal ..don't get it on any fruits or veg that you won't cook before eating   , especially soft fruit such as strawberries . The reason being is that urine whilst sterile at the outlet quickly becomes an e-Coli  propagator .

As E. coli isn't present in healthy urine, I wonder how it would get into the urine that is put on plants?  It seems a very low risk.

Because E.coli is common, if not ubiquitous, in the environment, and will quickly colonize a potential growth medium like urine, or fresh manure. There are thousands of strains -- some pathogenic, some harmless, some beneficial -- but small numbers can be beneficial and large numbers toxic. The tiny amount of E.coli in our guts grows rapidly in fresh feces exposed to air, hence the problem with using human manure.

https://en.wikipedia.org/wiki/Escherichia_coli

I think it is a risk so small as to not worry about it.  I wouldn't put urine on plants I'm just about to eat in a salad, but I have no problem putting dilute urine on salad that I'll be eating tomorrow, and then watering it in.  Of things to worry about, E. coli from urine on my salad is not even on my list.  Of course I wash the salad, because a bug might have been walking with his dirty little feet on it.

It has always been my understanding (per the book Teaming with Microbes) that the real issue is not "robbing" your plants of nitrogen, but that the soil becomes a fungal dominated soil with a higher acidity when copious amounts of lignin have been added as bacteria, for the most part, are unable to break down wood. Once the soil becomes too acidic, nitrogen fixing bacteria cannot live. This is good for late succession plants such as woody shrubs and trees, as they thrive in more acidic soils. For annual beds, however, bacterial dominated soils are preferable.

I am by no means a scientist and I typically do not like to rely on anecdotal evidence. However, I rotate between wood chips, straw, and chop and drop in my annual bed, depending on what is available. I definitely notice a difference in the seasons following the use of wood chips in the size and productivity of my plants. For my perennial beds, this matters much less, with the exception of my asparagus. It seems to prefer straw mulch exclusively!

**edited to add- I do not find any difference after application of wood chips if I add blood meal. In addition, I have only been doing this about... 15ish years? So, perhaps I have used wood chips as mulch for 5-10 seasons over the years? It certainly hasn't been a lifetime of experience, but I do feel as if it's enough to notice a difference.

Cheers!

chip sanft wrote:
Interestingly, Sharifi et al. 2014 found that in their experiment mixing wood chip bedding in with manure actually increased the availability of nitrogen to crops over the course of eight years.

I can attest to this. In my constant experiments with applying whatever I can get my hands on as mulch on my ornamentals and trees, this year it's horse bedding with wood shavings. It's been approximately six months, I started applying it in the fall, and continued through the winter. We are arriving at our spring (in the Southern Hemisphere) and everything looks huge, lush and GREEN. Because it's rained non-stop for about six months, the mulch has fertilized the entire 2 acre property.

Margarita Palatnik wrote:

chip sanft wrote:
Interestingly, Sharifi et al. 2014 found that in their experiment mixing wood chip bedding in with manure actually increased the availability of nitrogen to crops over the course of eight years.

I can attest to this. In my constant experiments with applying whatever I can get my hands on as mulch on my ornamentals and trees, this year it's horse bedding with wood shavings. It's been approximately six months, I started applying it in the fall, and continued through the winter. We are arriving at our spring (in the Southern Hemisphere) and everything looks huge, lush and GREEN. Because it's rained non-stop for about six months, the mulch has fertilized the entire 2 acre property.

I guess that is because initialy it takes some easily accessible  nitrogen present in the soil to start breaking down the wood   & your plants notice the change in levels . Then once the wood has rotted to a certain level it  replaces it  , the decay then carries on further till after seven or so years all the values of useful things tend to be much reduced .  
Here in Great Britain we know this as "  building the soil " , it's one of the reasons that farmers of old ( till around the mid 1960's ) used to use at least ten , two ton ( horse drawn ) farm cart loads of crew yard muck per acre in their five year crop rotations . It all went to hell in a hand cart when a two crop system  , nothing been left to go fallow  & man made chemical fertilizers came on the scene .

Please Help!  I would appreciate suggestions.  My garden is 3 years old.  The first year we killed the grass with a tarp and had a wonderful harvest.  The second year, we tilled, planted and added wood chips.  Again an even better harvest with less weeding of grasses.  The 3rd year we added more wood chips, anywhere from 2 - 6 inches.  We pulled back the chips, filled with compost and planted.  We have clay under a the topsoil.  My plants seemed stunted.  Small plants, little or no vegetables, yellow leaves and lots of bug problems.  Potatoes are awesome.  Now later in the season, the swiss chard along with any plants still performing, seem to be doing a lot better.  I'm thinking of spreading blood meal over the whole garden at the end of the season.  Is there more I should do?  Have I killed my garden?

Thanks for your help.

Debora Shumaker wrote:Please Help!  I would appreciate suggestions.  My garden is 3 years old.  The first year we killed the grass with a tarp and had a wonderful harvest.  The second year, we tilled, planted and added wood chips.  Again an even better harvest with less weeding of grasses.  The 3rd year we added more wood chips, anywhere from 2 - 6 inches.  We pulled back the chips, filled with compost and planted.  We have clay under a the topsoil.  My plants seemed stunted.  Small plants, little or no vegetables, yellow leaves and lots of bug problems.  Potatoes are awesome.  Now later in the season, the swiss chard along with any plants still performing, seem to be doing a lot better.  I'm thinking of spreading blood meal over the whole garden at the end of the season.  Is there more I should do?  Have I killed my garden?

I wonder if with all the amendments AND clay underneath, if maybe they're getting too wet and it's rotting the deeper roots.

I agree it might be too much moisture early in the season.  I had the same problem with my garden right after a flood saturated the soil.  The plants turned yellow and stopped growing.  As the soil dried out most of them recovered.

I'm also thinkin' that if you had a wonderful harvest, probably the soil ain't broke and shouldn't be fixed. I'd guess that the initial addition of wood chips improved drainage -- temporarily. But chips will hold water underneath the top layer, to a degree you might not believe til you dig down and discover a bog.

I've used sawdust and wood chips for mud control, and here's what I've found: Coarse sawdust wicks water upward, which tends to make for uniform moisture and no wet spots. But fine sawdust acts like a sponge, which becomes soggy easily, and wood chips act like a layer of plastic, producing a dry surface but keeping a wet layer just below the surface (and I mean wet as in "you could soak a rag in it"). I expect they work much the same in a garden as they do for a traffic area.

Sawdust from a sawmill's ripper saw is perfect -- has a consistent texture about like small aquarium gravel or cat litter. Planer sawdust is a poor second if it's all you can get, but tends to contain a lot of fines, chips, and splinters.

Do a soil test and what does it say?

Perhaps you ran out of one of the NPK aspects.  

I basically figure that once a garden is happy, we just want to replace what I took out of it in various forms of organic NPK.  I also support the bio life of the soil by adding tea from now and then and using natural farming inputs but I am just a pup in that.

Also, there is a possibility of something in the compost. Did you make your own or did you buy it? Was it made with plants or hay or straw, that was treated with newer generation herbicides, that do not degrade for years? Same applies to manure of animals who ate hay contaminated with that herbicide. They just started making those herbicides in 2007, so it is relatively new thing. They even have a name for it -killer compost.
Also, when you added wood chips, did you also add high nitrogen stuff like manure or urine?

Thank you for all or your comments and suggestions.  We made our own compost with all organic ingredients.  I'm not sure about the composition of the wood chips though.  Should I put blood meal on this year or wait and put around plants next year?

If you're trying to hasten decomp of the wood chips, then a little nitrogen fertz (watered in) would help feed the bacteria that eat the wood.  Just like using nitrogen to hasten decomp of an old tree stump.

So I'd say put light nitrogen on now and it'll be that much further along next spring.

When in doubt, a bit of urine or bloodmeal will give your plants a shot of N that they may be asking for.  

Something i heard bill mollison say on an old recorded permaculture design course is that wood chips on the surface use atmospheric nitrogen to break down. Does anyone know if this is true?

Bryant RedHawk wrote:Wood, when it comes in contact with soil, activates mechanisms in certain bacteria which then consume nitrogen as food so they can decompose the wood.
If this wood is sitting on top of the soil (fallen tree, dropped tree branch and so on) then these mighty bacteria will become active, but only to a depth of around 5mm.
This means that the answer to the nitrogen "robbing" wood is only involved in a minute area under and around the piece of wood.

Nitrogen is robbed from the soil due to composting woody debris. This generally follows along a 7 year rotation, where the first 7 years, the soil in trying to break down this wood and robs the soil of that ellusive nitrogen, but after 7 years, that nitrogen is given back into the soil.

Nitrogen in a real forest is nitrogen-nuetral because the soil was once 100% wood material. The top most layer is recent fallen leaves, twigs, sticks, etc and has hardly broken down, yet the deeper a person goes it can be readily seen that the wood is already broken down. Because of this constant rotation of new layer of wood to break down, and wood already broken down and giving back to the soil, nitrogen in the soil is both taking and giving. The reason ferns and other nitrogen loving plants thrive is because their roots are down in the already broken down woody debris. Considering it takes 600 years to make just 1 inch of topsoil, 7 years is but a day eqivilent in a forest lifecyle. Their roots are feeding off the nitrogen that is being RELEASED back into the soil, not last years fallen leaves.

Now when I clear a forest and put it into a field, is disrupts everything. Suddenly there is no more layers of soil. I am mixing freshly fallen debris into the soil. Because of the size of wood and the freshness therof, I experience a lot of nitrogen robbing. This shows up in my crops by stunting their growth. To overcome that I have to apply twice as much manure in freshly converted lands, but that over-application gets me beyond the nitrogen that is being robbed. Thankfully after about 7 years the nitrogen reverts back into the soil and for 7 years or so, I get to reduce my manure reirements to get the same yield.

If a person uses wood chips to spread out on their garden they are going to get the same thing. If it is tilled in deep, then the nitrogen robbing will be more accute, but if it is spread on the top of the soil, only the soil it comes in contact with will be robbed of nitrogen. In that case the benefit of wood chips is not fully realized; in that case the wood chips are being used to protect the soil from erosiion, to keep the soil moist, and to help thermally protect the soil from heat and cold. Those are all lofty results. So I am not saying they should not do it, they should, especially if their organic matter is way down.

Myself, I think putting in more wood chips, tilling it in, then adding more manure to compensate for the nitrogen loss is a much better plan. The wood chips will areate the soil, get more organic matter into your soil, and provide all the other benefits too, and what garden does not benefit from more manure?

What I take from all this is that what your soil life is like and what parts of the tree are used to make the chips, as well as the age of said chips, will determine the nitrogen draw-down.

According to the chart Craig posted, the wood most suitable for mixing into depleted soil would be fresh branch wood (ramial wood?) due to higher nitrogen content. Given the option, I would only chip bark and stem wood for mulch, and ideally, I would leave the stem wood intact for hugelbeets, where the deeply-buried lignin-rich material would prolong the life of the hugelbeet-as-nurselog, while not affecting the nitrogen levels of plants growing out of them.

I could probably get on board with the suggestion that stem wood shouldn't be chipped in a buried context, as that just increases surface area exposed to the soil, and it might be a good rule of thumb that the lower the levels of nitrogen in the woody material, the larger the individual pieces should be.

I also wonder what effect seasonality has on the nitrogen numbers. If harvested and chipped at the height of sap production, I think even stem wood would probably have increased levels of nitrogen. I am only guessing, but wouldn't liquid tree nutrient sitting in chipped wood in the soil act as food for soil bacteria and fungi?

I think cases of observed nitrogen drawdown might be extreme cases. Travis, indulge me for a moment. Have you tested the nitrogen levels, or are your conclusions based on plant growth? If there was anything else that could be going on in these situations that was related to the application of wood chips but not a nitrogen draw-down issue, can you speculate as to what it might be?

One experiment I haven't yet been able to try is to keep a pile of woodchips that I refresh regularly, that I inoculate with a compost extract with each refresh. If the chips are already hosts to the bacteria and fungi that will break them down, and if nitrogen is added with them, any negative effect, I think, might be minimised.

-CK

Travis Johnson wrote:Now when I clear a forest and put it into a field, is disrupts everything. Suddenly there is no more layers of soil. I am mixing freshly fallen debris into the soil. Because of the size of wood and the freshness therof, I experience a lot of nitrogen robbing. This shows up in my crops by stunting their growth. To overcome that I have to apply twice as much manure in freshly converted lands, but that over-application gets me beyond the nitrogen that is being robbed. Thankfully after about 7 years the nitrogen reverts back into the soil and for 7 years or so, I get to reduce my manure reirements to get the same yield.  

So what you are doing Travis is called complete disturbance, then you are coming back to change the growth pattern from forest to grass land.
In such a situation you would find leaching of N,P and K rampant since you have taken nature out of the equation, just like a crown fire and almost like a lava flow, the flora that was, is no more.
That means that you have disrupted the natural mineral users and processors, which are now dead or very badly torn apart.
I am not surprised that it takes so long for the soil to recover.
This sort of thing does happen when there is such a large disturbance.  

What you are describing is what modern agriculture does, Total disturbance back to pre- part one of the process of succession.

However, in a situation that doesn't follow total disturbance, there would be far less loss of the prime three nutrients because the microbiome would not be ripped apart.

Redhawk

Chris Kott wrote:I think cases of observed nitrogen drawdown might be extreme cases. Travis, indulge me for a moment. Have you tested the nitrogen levels, or are your conclusions based on plant growth? If there was anything else that could be going on in these situations that was related to the application of wood chips but not a nitrogen draw-down issue, can you speculate as to what it might be?

I have done extensive soil testing, and plant observation both, and the results are pretty conclusive. Soil reports, observed inverted yellowing in the plant leaves, and of course yield...what interests me the most.

One observation I have noted on here is that people on Permies often cite failed Hugels, yet mine have always been succesful? Why have some failed, and mine have not? I think others might be failing because they are not using decayed wood...or at least wood that is not decayed enough. The wood I have always used is not just deadfall, but fallen onto the ground, broken down, and nearly crumbling wood; it is about as close to soil as a person can get. So a simple real world test is to make two hugels; one out of dead, but "fresher" wood, and one out of dead crumbling wood, and see which produces the better yeild of the crops above. This sounds simple, but that is really what true farming is all about...more food between the lips for less work performed.

It may be interesting to note that when my family cleared one of our fields in the year 1800, they noted "the field yielded grass over a mans head in one season, whereas in England it barely reached the knee."

Because of the layout of our farm, there is 30 acres that has always been old growth forest, never having been cleared. This was proven by reddish soil cropping up as I logged it. This was iron in the topsoil; had the land been logged, tilled or pastured, that iron would have long rusted out which is what gave it that reddish look.

I have cleared a lot of land; on both my farm, as well as for others as a land clearing contractor, BUT this is the first land I have ever cleared that was old growth, so I will be able to observe yields, nitrogen leaching, etc. What would be really interesting is to land-clear using different methods, like doing it how my forefathers did, with more modern methods, etc and see what the results were. For instance I know in the old days they burned the brush which was poor mans fertilizer at a NPK of 0/1/3, but since they were using hand tools, I bet a LOT of brush was burned too making for plenty of biochar/fertilizer.

This is that 30 acres soon to be into productive farmland. The field in the background was cleared in the year 1800.

Chris Holcombe wrote:Something i heard bill mollison say on an old recorded permaculture design course is that wood chips on the surface use atmospheric nitrogen to break down. Does anyone know if this is true?

It's not the wood chips that use atmospheric nitrogen to break down. There are free living nitrogen fixing bacteria, such as azotobacter for example, which can convert atmospheric nitrogen without a host plant like a legume, which other nitrogen fixing bacteria called rhizobia need in order to convert atmospheric nitrogen N2 into the ammoniated form NH3, which living things can use. So knowing this, if nitrogen fixing bacteria are present where the wood chips meet the soil, then it's the nitrogen fixing bacteria that can provide the needed nitrogen that the other decomposing microbes need in order to break down those wood chips.

Don't recall if anyone mentioned it, but one other thing to be cautious about: sawdust from treated lumber. It can kill everything it touches. We have a finishing mill here that produces an infinite amount of both fresh and mulched sawdust, and it breaks down very fast, but have learned not to use it in a garden -- plants do poorly or won't grow at all, and whatever they treat the lumber with (probably a fungicide) apparently lasts a long time, even after the sawdust has turned to mud. Very unlike sawdust straight from the tree trunk.

I have a rotten tree stump that breaks down more and more each year. I planted an apricot tree right next to it and it’s now the healthiest, strongest tree in my yard. I pull the tree stump apart each year as it rots, and now found apricot roots happily growing right through the whole stump.