Spreading Sawdust on Trails, Fields, or Woods
Sawmill operators discuss when and where it might be okay to spread sawdust around. March 9, 2010
Question
I'm always trying to figure out what to do with the sawdust from my Wood-Mizer mill. If I spread it on my main skid road into my forest, am I creating a fire or weed hazard? Does this sound like a reasonable way to deal with sawdust since it is so difficult to burn? I've seen people use it for foot paths and it seems to choke weeds out.
Forum Responses
(Sawing and Drying Forum)
From contributor A:
No! It holds moisture on the skidder trail and when you come back through, it will rut deeper. It will make pot holes deeper.
If you have bare ground it makes good cover and Bermuda grass loves to grow in it. I spread it out in the fields and it has helped our grass production. It mixes into the garden fine and does not seem to heat up as bad as larger wood chips. Lots of farmers here put it in the floor of chicken houses for about 6 months then shovel it into the garden. Not good on road ways.
From contributor S:
A horticulturist friend of mine advised me that sawdust is great for the growth of any woody plant, either trees or bushes. So perhaps take the dust up to the area where you've been cutting the trees and spread it around. I've also grown potatoes planted directly into old sawdust, but this will depend on how much rain you get.
From Professor Gene Wengert, forum technical advisor:
Because of the high surface area of sawdust per volume (compared to chips, for example), sawdust will tie up most of the nitrogen in the soil as it decays. Eventually the nitrogen is released. Hence, the plants in a garden and smaller shrubs will turn yellow until the wood is decayed. For this reason, nitrogen should be added to the sawdust when it is first spread in a garden or other area when green growth is desired.
Additionally, some species also have insecticide and fungicide properties. Some species, walnut most notably, have herbicide properties. Many is the gardener that has used walnut sawdust or chips in a garden and found that tomatoes won't grow. A thick layer of wood will also encourage certain mold growth on the surface which can look ugly.
Finally, sawdust has a high concentration of some minor elements, so putting it in the forest concentrates these elements in a small location. Therefore, if sawdust can be spread, it requires a special permit in Wisconsin and probably other states. Obviously, sawdust in a garden over several years will concentrate these elements, which is not desired.
All in all, the use of sawdust in the woods is not a bad idea, but there are special considerations. Your local Dept of Natural Resources or County Extension people should be able to advise you.
I have seen a few operations that add nitrogen, manure, and soil together, and then aerate to make a compost mixture. Again, avoid walnut and other herbicides.
From contributor C:
If sawdust has a concentration of certain elements and the sawdust came from logs and the logs came from the woods, why isn't the ground in the woods full of these concentrated bad elements from all the trees and limbs that fell and rotted? I am confused as to how sawdust can be bad if put in the woods, but wood from the same tree would not be bad. I just walked through a woods that has never seen a chainsaw and every piece of wood ever grown there fell to the ground and was incorporated into the soil, and the woods was growing just fine. Where 400 year old oaks fell, new growth was growing just fine. Donaldson's Woods at Spring Mill State Park in Indiana.
From Professor Gene Wengert, forum technical advisor:
Good question indeed. The concern is whether the chemicals or elements are changed from being widely diffused to concentrated. When put on a trail, they are concentrated compared to being located throughout the forest. (I do not make the laws or the concerns; I am merely a messenger.)
From contributor C:
Then why doesn't mulch cause a problem? Especially hardwood mulch made from ground pallets that is dyed. I see lots of homes that have gobs of mulch around trees. Businesses have lots of mulch around them. So that begs the question, why is mulching my hayfields or woods with sawdust bad and mulching around homes and businesses just fine? Mulchers do right of ways grinding entire trees into slivers which are put on the ground, sometimes in big mats because there is so much of it. Maybe some laws need to be changed. Why is it illegal to mulch my pastures with sawdust, but not my yard trees?
From Professor Gene Wengert, forum technical advisor:
Politics or special interest groups.
From contributor C:
The original question was readily answered by people that have been there and done it and observed the consequences. I would guess most folks won't put sawdust on their log roads. Doesn't take a law. If anyone knows of the science or the reason there are laws against dumping sawdust on fields, I would be interested.
From the original questioner:
I'm now convinced I shouldn't spread sawdust on my skid trails. However, serendipitously, I've just read an article on the effects of herbicide treatment of weeds in grassland areas. Herbicides release a lot of excess nitrogen into the soil. Conversely, sawdust depletes nitrogen in the soil. Could there be a win-win situation in spreading sawdust on fields sprayed with herbicides for weeds? The question would be what is the right ratio?
From contributor D:
The nitrogen depletion during sawdust breakdown is temporary. Sawdust actually contains a certain amount of nitrogen... just not enough to break down its carbon. Once the carbon is broken down, the nitrogen that was taken up during the breakdown process is released, along with the nitrogen originally in the sawdust. The net effect is more nitrogen in the soil, which isn't a bad thing.
I'm curious as to how long the herbicide in black walnut is persistent in the soil? I couldn't find that mentioned anywhere.
From Professor Gene Wengert, forum technical advisor:
I was surprised to see that wood contains nitrogen, as I thought the nitrogen in wood was so small as to be insignificant. Can you give me a source (maybe on the Internet) with that info? Thanks.
From contributor D:
I was stating that based on memory. At your request, I found the Colorado State University Extension website, where they state a carbon to nitrogen ratio of 400:1, a much lower ratio of C/N than the sites I sourced in the past suggested.
It was mentioned earlier that certain toxins are released when wood breaks down. Does anyone have more info on this?
From contributor A:
The thing we seem to need to add the most is lime. Ammonia helps supply the nitrogen that we need but with the sawdust from the WM being so fine, it seems to break down quicker without heating up so much. When spreading out on the field, we only put it 1/2 inch thick and often do a light disk, then fertilize. I have noticed that Bermuda grass loves the sawdust piles. Our soil is mostly clay and some pretty old worn out dirt here in the Ozarks. Those who put it in the chicken houses have the nitrogen added by the chicken poop, so it is a win/win deal.
From contributor S:
According to NC State University, sawdust is .2 % nitrogen.
From contributor F:
As far as the persistence of growth inhibitors from walnut trees, as I remember, they break down in weeks or a few months at most. Of course around a living tree that might not apply.
From contributor B:
I have been told that if walnut is first composted thoroughly, then added to the garden or around trees and shrubs, you are fine. I mix my tree chips, sawdust, leaves and goat barn cleanout into a big pile and wet it good, mix it every couple of weeks and presto - great compost. A bit of work, but go price it by the bag.
From the original questioner:
Okay, not to complicate issues any more, but does anyone know the beneficial or negative properties of ash from burned fires? Would ash alone benefit pasture fields? How about ash mixed with sawdust?
From contributor G:
When I ran a pallet mill, I put the sawdust in my garden (2" to 4" each year). For the first 2 -3 years I had to add N, but after that I was able to cut way back on my fertilizer. This effect lasted 5 or so years after I quit putting sawdust on.
