Oak Sawdust Compost Chemistry

I posted here about six weeks ago that I brought 5 free dump truck loads of oak-sawdust compost home. It's from an old pallet manufacturing company near us where they had big sawdust piles out in the weather. I picked the darkest looking stuff I could find - it's at least 15 years old (maybe 25 or 30) and it looks and smells like heavy, black, rich soil.

Before planting, I tilled about 2 pickup truck loads of the compost into my 36' x 36' garden. I think it must be pretty high in N because my corn, beans, zucchini, melons, cucumbers, etc. are extremely big, green, and lush this year. The tomatoes are doing fine with it, and I made sure they were planted deep enough that the roots started out below the composted layer. The shallow-rooted pepper plants were transplanted right into the compost layer, and they got fertilizer-shocked at first. They're doing OK now, I think the roots got below it.

Now, I've covered the ground in my rows of tomatoes and peppers with grass-clippings mulch, and I won't mess with them any more. Yesterday I tillered between the rows of other veggies, and I think I'm going to put 4 to 6 inches of that compost on top of the ground between those rows. I'll keep it about 3" away from the plants and I won't till it in - then I'll spread grass-clippings mulch on top of that. The compost should act as a side-dressing, keep the crabgrass and weeds from sprouting, and bring up the soil level in the garden.

My question - I'm sure this sawdust compost is high in N, but do you suppose it's got any P and K in it? I'm operating blind right now until I get a soil test in the winter - and what I need now is phospate for good fruit production on these lush nitrogen-laden plants. I'm kinda afraid to add more P because for all I know this compost may already be rich in it.

Actually, it's kind of the opposite as far as sawdust is concerned. I would guess that your sawdust is completely composted or that you have other factors adding the nitrogen because in the process of breaking down, wood uses up nitrogen. So unless it was added in some other way, I doubt that added any nitrogen to your soil at all.

If you get no blooms on your plants, you know that you have nitrogen and perhaps little else, other than nice, fluffy soil - the nitrogen gives you the big, green leaves. Missing phosphorus or potassium would be a culprit if you plants look great but produce little.

HTH!

Pagancat - Thanks. I decided that I'm operating blind on this compost, and I've used so much of it in my garden I better find out what's in it. I dropped a sample off today with our University extension for a soil test, and I'll have the results in a week or so.

I've tilled some of it in, but mostly I've spread it as a mulch in the entire garden around the plants 3"-4" deep. My concern now is that if it's not fully composted it may deplete nitrogen in the soil after I till it under in the fall - and if so, I'll have to compensate. I also want to know if it's got any Ph and K, and what the acidity is.

Whatever the chemistry is, it seems to be beneficial. There are lots of earthworms in it, not just the manure worms but nightcrawlers. My sweet corn variety that normally grows 7' tall is 9' tall this year already, and the ears are big. I've got lots of blooms and green tomatoes, and the zucchini, cucumbers, melons, and beans are doing good too.

I'm anxious to see how that test comes out. There's still six acres of the stuff available, for free, about 1/4 mile from my house - and I may want to go get some more.

Hey, no problem. The one source I found on sawdust did say that it would it compost fully in approx. 4 years - I'm sure it would depend on conditions and type of wood, but surely 15 would have taken care of most of it.

If your plants look good, and are producing well, I'd say whatever is in it is beneficial and you'd best grab it while you can!

Enjoy the fruits!

Yeah, I think I'm in good shape. I talked with an old neighbor yesterday, and he said that pallet company was operating there since 1952. Since I picked the oldest and blackest of the compost, what I've got is probably very old.

Also, they were sawing green oak tree trunks straight out of the woods. I'd think wet sawdust like that would make compost much quicker and break down better than dried lumber sawdust.

Sure....

Okay, trying to contain my jealousy here.... >grin< ... quite the score, I'd say!

Well, Tennessee is the next state over - I've driven that far to go crappie fishing!

If you can get a big truck and want an Ozarks vacation, I'll load you up!

Thanks, you! >smile< ....

if it's 15-30 years old it's already broken down.

I used the compost as a mulch about 3" to 4" deep between my corn rows. Even if there are no nutrients in it, it'll keep weeds from sprouting, stop erosion, and keep moisture in the ground during the season. After I till it under in the fall, it'll put more organic matter in my soil - and if there's some good fertilizer in it, so much the better.

I should have the results of that soil test back soon, and I'll post it here.

To heck with the compost, I'm coming for the corn!

"To heck with the compost, I'm coming for the corn!"

Well, I'd share that too. lol

Aren't you a good guy! What am I doing in TN?

I got the soil test results back today on that oak sawdust compost, and it's interesting:

pH: 5.2 - low
Phosphorus: 5 lbs./acre - very low
Potassium: 66 lbs./acre - very low
Calcium: 1339 lbs./acre - medium
Magnesium: 67 lbs./acre - low
Organic Matter: 81.1%
Neutralizable Acidity: 2.0 meq/100g

The note with the test results starts out: "Sam, what are you testing with such high organic matter, or is this a printing error?"

I had taped a note to the test jar explaining that this isn't my garden soil, it's very old oak sawdust compost that I'm using as mulch then tilling into my garden. Apparently the Horticulture Specialist who writes the recommendations only reads the computer printouts and didn't get that information. I'll get ahold of him and get his recommendation based on that info.

The nitrogen content is still a big unknown, but this compost looks like pretty harmless stuff - there's not much in it. After I plow it in I'll have to add some (P) and (K) as well as some lime to balance the soil's acidity. If the nitrogen is low in this compost, like everything else is, I wonder how much nitrogen I'll need to add to replace what it depletes after it's plowed in.

I've got good garden soil, but it has some clay and makes hardpan when it dries. I bet this compost will fix that.

LOL - I didn't realise you had sent in the compost for the test! It is *very* interesting, though.

Just an idea -there's an awful lot of stuff you can use to bring the pH back in line, along with the nitrogen, etc. that are longer lasting and healthier in the long run than adding straight lime and fertilizer. If you have the machinery to plow, etc., why don't you plant a legume as a green mulch/ cover crop? Soybeans, clover, vetch, etc. - there's another thread where Garden Mermaid talks about a few of them. Compost does break down at some point, so it can only help maintain that great tilth you have going with the sawdust. I'm amazed at the difference clover has made in my soil - there's about 3" of black stuff sitting on top of that thick, gummy, gold clay I have so much of...

why don't you plant a legume as a green mulch/ cover crop?

I think I'll do just that, if I can find something that'll make a stand in the few weeks between the end of my garden and a hard freeze. I planted annual rye one year and let it stand all winter, but a legume would be much better.

I just got off the phone with the horticulture specialist at our University extension. Once he was aware that it was compost, not my garden soil, that they tested for me - he thought it was great stuff.

The compost doesn't have much in it as far as nutrients - and that's good, it won't overdose the soil with anything. He said I'm right in using it as a mulch between rows then plowing it in. The soil pH will soon return to normal, and the compost will take a little nitrogen while breaking down in the soil and then it will become a nitrogen source in the soil. It's very, very good stuff as a soil amendment according to him.

I've got 5 dump truck loads of that compost, and I think it's going to come in handy for years to come. I'm going to harvest my corn this weekend, and I'll pull the green corn stalks and put them in a big compost pile. Then, I'm going to use the tractor and bury the corn stalks with sawdust compost and wet it all down. That compost pile is going to cook!

Yeah, baby!