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Probably an Unanswerable question...

Posted by yardtractor1 10 (My Page) on
Fri, May 23, 14 at 19:06

...but is there any research that states the minimum amount of organic matter necessary (e.g. weight/volume of X OM per time period) to sustain a "healthy" level of diverse soil micro-organisms?
In an effort to remove some of the variables, let's say the plot is a 10'x10' raised bed of sharp sand kept at a temperature between 65 and 75 degrees F. and kept at 15-30% moisture content. (or conditions of your selection if necessary to the answer) If a source of research is unknown, opinions with a supporting rational are welcome.


Follow-Up Postings:

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RE: Probably an Unanswerable question...

Let me tell you a story. I was recently re-leveling a brick over sand patio. This involved lifting low bricks, adding sand, and so on.

The bricks had been down for at least 30 years, over what was originally sand (now more dirt-looking) ... but I kept finding earthworms, one every 2 or 3 bricks.

So life finds a way.

(That said, I think you'll hear recommendations for 5-10% OM as standard, and I'd go with that for a "healthy and diverse" environment. That should be "diverse" OM as well, rather than something uniform like peat.)


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RE: Probably an Unanswerable question...

Since you asked for a study ...

Organic Matter Application--Can You Apply Too Much?

If you read it, you'll find that the problem isn't the OM itself, but the nutrients that rode in with it. An aggressively improved field had too much nitrogen to be ideal for a commercial pumpkin crop.

(I report this, but I do think it is a bit at cross-purposes to common raised bed advice (50% compost), or my own container experience (60% compost?). Despite the theory, higher OM might work in practice. Heck, 5-1-1 potting soil is 6 out of 7 parts OM, or 85% OM.

Possibly the thing that ties it together is that OM is not just generic OM. Slow to break down OM is doing something different in the soil or pot than fast to reduce stuff.)


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RE: Probably an Unanswerable question...

Thank you for the reply and the link, It was an interesting read. I guess what I'm really looking for is: if I was a micro organism farmer, how much OM would I need to raise and feed a herd in a mason jar?


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RE: Probably an Unanswerable question...

The answer to that question is in your garden.
If you see a lot of earthworm activity that would indicate that you have an active Soil Food Web.
So how much organic matter does your soil need? Enough to get the Soil Food Web active.

Here is a link that might be useful: Soil Biology Primer


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RE: Probably an Unanswerable question...

I have been using a lot of Used Coffee Grounds lately.
UCG helps bring in earth worms, they LOVE the stuff.
UCG also has a very even makeup as to particle size.
excellent for drainage (to add to clay), it holds water, mixes easily etc...

Some people told me not to add it to soil without composting it fully, but i add it to the top as a dressing and the sun breaks it down in 2-3 days to a brown color.

I have added it straight to soil for tomato and papaya seeing no negative effects on either i did add course sand to help drainage as well though.


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RE: Probably an Unanswerable question...

Unanswerable ... because any area has a distinct assortment of species adapted to the local conditions. The species in healthy spruce forest in the PNW and the species in healthy Anza Borrego Desert soil aren't the same.


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RE: Probably an Unanswerable question...

My clever attempt to be coy is an utter failure.

As I don't know who reads this forum and I don't wish to offend, I'm going to be a little less generic while still protecting the innocent. I know one does not visit this site but I'm unsure of the other. I think the other only reads certain lawn care experts and probably does not visit.

As there has been some "uncomfortableness" in this forum lately, I would really appreciate that this not degenerate into an organic vs synthetic debate, "true organic" vs "pseudo organic", editorials on adverse environmental impacts or denigrate the parties.

The scenario is two neighbors. Both have beautiful KB lawns.
No disease, insect or thatch issues over the past 4 years or more.
My own lawn care is much more similar to one than the other so I admit to more than just a passing interest.

The relevant facts:
To my knowledge, soil is identical in structure to my own. TEC: just under 10.
Neighbor #1 uses synthetic fertilizers. Applies 1 and 1/2 pound of N before June 15 in 1/2 pound applications. Applies 1 pound of N via Milorganite sometime between June 15 and August 15 primarily for the iron or to give the lawn a "needed kick". Applies 3 pounds of N between September 1 and December 1. Mulch mows.
Neighbor #2 uses organics. Applies 1# of N via Milorganite every two weeks between April 15 and May 15. Applies 1# of N via Nature Safe every 2 weeks from May 15 to July 15. Applies 20lbs/m of alphalfa on August 1. Applies 1# of N via Nature Safe every 2 weeks from September 1 to October 1. Applies 1# of N via Milorganite every 2 weeks during October. Applies 2# of N via Milorganite at Thanksgiving.

Neighbor #1 states that the grass clippings and the one annual application of Milorganite is sufficient to provide all the microbial activity necessary to sustain and efficient and healthy lawn.

Neighbor #2 states that you can neither apply too much organic fertilizer (short of smothering the lawn) nor have too robust and diverse soil web. #2 states that any excess nitrogen produced by the abundant application of OM is simply stored by the expanding micro-organism web until needed.

Both point to their 6+ and 8+ year old beautiful lawns as proof.

My only question is: Which neighbor is correct?


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RE: Probably an Unanswerable question...

Both or neither. The only way to know which one has the healthier soil is to dig in and look. Just as a person can function quite well, for a time, on drugs so can lawns. But then where the soil is not a good healthy soil little problems such as plant diseases and insect pests start to become noticeable and problematic.
We know today that soils, even good healthy soil with adequate amounts of organic matter, do not store excess Nitrogen, or Phosphorus, and what is not needed will flow out of the soil with the excess water and enter the ground water system polluting that water we drink and prepare our food in.

Here is a link that might be useful: The Nitrogen Cycle


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RE: Probably an Unanswerable question...

What it really "proves" is that modern strains of Kentucky Bluegrass tolerate a wide variety of fertilizer sources and application schedules. Making it "idiot proof" has been a breeding goal.

More to the point, what are the watering and mowing habits of these two?


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RE: Probably an Unanswerable question...

I think there are going to be a lot more variables (as the previous post alludes to) than just the soil microbial community. Even that parameter (actually a multi-parameter collection in reality) will depend on several things, not just OM addition.

Completely untreated native soil from most places will have millions or billions of microbes per gram. Thousands of species of aerobic and anaerobic bacteria, actinomycetes, fungi, etc. How can you hope to ever compare apples to apples given two yards to sample?

I submit that you could do it by comparing the quality of the crop. Strength and health of the lawn, drought and disease resistance, etc. The proof is in the pudding.

This post was edited by toxcrusadr on Tue, May 27, 14 at 13:13


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RE: Probably an Unanswerable question...

I submit that you could do it by comparing the quality of the crop. Strength and health of the lawn, drought and disease resistance, etc. The proof is in the pudding.

I'd also add Return On Investment - not that it has to drive all things, but I think efficiency matters.


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RE: Probably an Unanswerable question...

When I dug up part of my lawn that was dead, back when I had a lawn, and added home made compost and dug it in and replanted the grass seeds, they did grow much better, but lawns can do great on just chemical junk, if you want to do it that way. It is like the difference between buying a brownie mix in a box and adding water or making your brownies from scratch.


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RE: Probably an Unanswerable question...

And of course the full life cycle analysis of 'compost vst. fertilizer' includes such things as nonrenewable resource use, the impact of mining fertilizers, climate effects of transporting materials, CO2 emissions from burning gas to make nitrates, etc. etc. All this is beyond the scope of the OP's question though.


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RE: Probably an Unanswerable question...

Thanks for the respones.

Toxcrusadr. Interesting point and surprisingly simple: "The proof is in the pudding". As both lawns are healthy with no need for herbicides, insecticides or unusual watering, I need to get neighbor #1, who uses the least amount of OM to make some adjustments, or I suppose I could use my yard and start reducing OM input (reduce Milorganite and lawn clippings annually) until there were visible adverse affects (disease, insect infestation, lack of water retention and just general lack of turf health). That would take years and I'm not sure if I would recognize the adverse effects to look for that were a direct result of the reduced OM rather than something that would have occurred in spite of any change..

Thanks.

Edit: any suggestions of signs that would indicated an unhealthy level of microrganisms would always be appreciated.

This post was edited by yardtractor1 on Wed, May 28, 14 at 21:45


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