Soil Test Results on Compost

[Ozark]

Three years ago I asked the electric company tree trimmers to dump wood chips on my property. They left me a mountain of them and I did nothing further to compost the chips. I got the chips in the summer, so there were a lot of green leaves included which I know helped break the wood down.

Now, deep in the pile I've got what looks and smells like the best black soil ever. I dug into it last week and sent off a soil sample to our University Extension. Got the results back today and I'm very happy with it, but I have some questions. The acidity seems a bit alkaline for veggies, and the minerals are high as well. I'm building raised beds for a new garden; tomatoes, peppers, squash, beans, okra, etc. Should I fill the raised beds with this compost alone, or should I mix it with topsoil or something else that's a little more neutral? What do you think?

Here's the soil report:

"pHs 7.5 (high), Phosphorus 512 lbs/ac (excess), Potassium 1779 lbs/ac (excess), Calcium 13380 lbs/ac (high), Magnesium 1088 lbs/ac (high), Organic Matter 44.4%" (Note, I don't know where they got that - it's 100% organic compost!).

These numbers make the compost seem VERY rich, and I'd be concerned if it were not for this written summary at the bottom of the soil report:

"Your soil test report reveals a soil that is nutritionally well suited for vegetable production. No nutrients other than nitrogen are needed at this time. Nitrogen fertilization rates and timing are determined by the specific vegetable crop. I recommend retesting your garden soil in 2-3 years."

So - maybe "excess" Phosphorus and Potassium don't hurt, and a pH of 7.5 is OK also? The lab says it's OK and I'd really prefer to use it straight - what do you think? Thanks!

[Dutch]

Hi Sam,
Did they indicate what the sulfur levels were at?
Dutch

[Ozark]

Originally Posted by Dutch

Hi Sam,
Did they indicate what the sulfur levels were at?
Dutch

No sulfur level given. Everything in the report is what I posted above.

Something else that makes me think the compost chemistry isn't too far out of whack or toxic in any way: When I dug deep into the pile to get the sample, I encountered some big earthworms, on a 25 DEGREE DAY IN JANUARY! They were dormant and hardly moving, but they looked healthy.

I covered them up again before they froze.

[Dark Rumor]

I just did a soil test on my raised beds and earth boxes and both were high in all categories. I was told to add only nitrogen and lime, my ph was at 6.4.

I asked the university if I could mix in additional peat moss to dilute the high levels of fertilizer and minerals and they said that adding peat moss would help dilute the high levels. So I am taking out some of the old peat moss and adding new peat moss to dilute the buildup of fertilizer and minerals.

[Worth1]

I think 6.4 is perfect for tomatoes.

[Dutch]

Sam the PH may have been higher in the sample from the center if the compost became very hot and ash formed in that area.
The 44.4% may be an indication that it is not fully broken down yet.

At this point I think its best use would be as a top dressing.
Please view the chart on page 2 at the following link; https://www.uvm.edu/vtvegandberry/Pu...Production.pdf

Dutch

[bjbebs]

I have been using decayed wood chips for many years. Utility contractors, private landscape firms and one municipality that vacuums leaves have been dumping on a property I own. For the most part these are clean chips. The piles are separated based on age and stirred with a loader. Some of these piles start out over 20" high but with repeated mixing break down quickly. Like Sam said, green leaves mixed with wood heats a pile up overnight.
After 2 years the chips are tilled into already rich soils. These areas are cover cropped, tilled again and are ready to go. I would never use decayed chips as a stand alone product in a raised bed. It's not that they wouldn't grow good plants, they would. But to get all the benefits they need to be mixed with existing soils. The chemistry that happens is pure magic.

Originally Posted by bjbebs

I have been using decayed wood chips for many years. Utility contractors, private landscape firms and one municipality that vacuums leaves have been dumping on a property I own. For the most part these are clean chips. The piles are separated based on age and stirred with a loader. Some of these piles start out over 20" high but with repeated mixing break down quickly. Like Sam said, green leaves mixed with wood heats a pile up overnight.
After 2 years the chips are tilled into already rich soils. These areas are cover cropped, tilled again and are ready to go. I would never use decayed chips as a stand alone product in a raised bed. It's not that they wouldn't grow good plants, they would. But to get all the benefits they need to be mixed with existing soils. The chemistry that happens is pure magic.

Excellent info ... common sense too. Thank you!

[zipcode]

I think maybe you got some numbers mixed? K ten times lower than Ca, and K is 'excess' while Ca is only 'high'?

[Worth1]

The compost in my opinion needs what I call sharp sand nixed in with it.
Or even decomposed granite.
Some people use sandy loam but I am slowly getting away from it due to the quality.
Another thing to consider is the worms are hauling the decomposed material deeper into the soil.

[brownrexx]

Organic can refer to the way something is grown with all natural or approved materials but in this case they are talking about organic material which is material that has not broken down yet. Think of it as fiber.

My organic garden has 10 - 12% organic material but the average in my area is 4%.

If your % of organic material is too high it can cause nitrogen depletion as it decomposes. I saw this first hand when I added a LOT of chopped leaves to my garden and planted peppers. The plants all turned yellow. I fed them nitrogen and by the end of the summer they were all green again but my harvest was reduced.

Excess nutrients are not necessarily a good thing. I also have an excess in my garden as revealed by my soil test so I have stopped adding so much compost to the garden. Excess nutrients can cause stunting of plants and excess calcium leads to a higher pH which you have seen.

Excess nutrients can interfere with uptake of micro nutrients and excessively high calcium can interfere with magnesium absorption.

I would also recommend what others have said and that is to mix your compost with other soil to dilute the excess.

Edited to add that I just looked at my most recent soil test report from Penn State and saw this note:

"Soil nutrient levels exceeding crop needs can be as bad as deficient levels. High soil nutrient levels might not only might represent an economic loss, but they may also result in crop, animal or environmental problems. Very high P levels (above 310 lbs P2O5 /acre of 140 lbs P/acre) in the soil may lead to nutrient deficiencies especially of iron and zinc. If K, Mg and/or Ca levels are high, serious nutrient imbalances can occur. When K levels are above the 5% saturation; Mg levels 15% and Ca 80%, soil nutrition is beginning to get out of the optimum range. Use best management practices to avoid increasing nutrient levels that exceed crop needs."

[Ozark]

Lots of good thoughts and information have been posted here in response to my questions. Thanks, everyone!

I just spoke with the University of Missouri soil scientist who ran this test and wrote the report, and his input matches a lot of the answers here. He says he should have realized this material was compost and not soil when it tested as 44% organic matter, that just slipped by him.

As most here have said, he thinks this compost should be mixed with something else in my raised garden beds. He suggested getting some good topsoil hauled in, to be mixed at the ratio of 2 parts soil to 1 part compost. He said I should look at the soil I'm buying first to see that it's pretty much free of rocks, doesn't have too much clay, and that it appears and smells like good dirt for growing things. Makes sense to me!

The fellow I spoke to is also a vegetable gardener in raised beds, and he mixes soil and compost in just the way he is advising me to do. He says the compost chemistry will straighten right out when I do that - pH will move into the right range, and the high and "excess" nutrients in the compost will mean that I'll only need to add straight nitrogen fertilizer to those beds for years to come.