What is the difference between soil and compost? And the importance of soil

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  • Elisabeth
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What is the difference between soil and compost? And the importance of soil

Dear all,

I used to be under the impression that really mature compost is somehow pretty similar to soil, but after some posts and tweets by Joe Turner I realised that I was wrong (see also a related forum thread about material removed from UDDTs and composting toilets - click here ). As other people might be similarly in the dark as I was about what "soil" really is, I am copying here some tweets that I exchanged with Joe and Susi Batstone on this topic. I hope you find this interesting.

Elisabeth von Muench ‏@EvMuench 10. Apr.
What would one have to do to turn #compost into #soil?

Joe Turner ‏@bucksci 10. Apr.
err... leave it for hundreds of years..

Elisabeth von Muench ‏@EvMuench 10. Apr.
What happens during those 100s of years that technology could not mimic in some form? How about mixing compost and soil?

Elisabeth von Muench ‏@EvMuench 10. Apr.
And would you say that the lead paragraph here describes #soil well? en.wikipedia.org/wiki/Soil

Susi Batstone ‏@SusiB348 10. Apr.
Add minerals (Clay, silt, sand, rockdust) and indigenous soil microbiota to compost, then it will function as soil.

Joe Turner ‏@bucksci 11. Apr.
what Susi said eg see www.futureterrains.org/portfolio-item/artificial-soil-eden-

Joe Turner ‏@bucksci 11. Apr.
even this is just "soil-like" but is getting more like soil all the time.

Joe Turner ‏@bucksci 11. Apr.
of course the traditional method is to plough in organic matter. Quickly becomes incorporated into soil.

Joe Turner ‏@bucksci 11. Apr.
that page is much too long and tries to cover much too much of a complex subject. So the lead is not really very helpful.

Joe Turner ‏@bucksci 11. Apr.
pedogenesis is the study of how soils form, but even this is not really easy to explain en.wikipedia.org/wiki/Pedogenesis

Susi Batstone ‏@SusiB348 11. Apr.
Ploughing not usually the best solution - surface mulches, zai pits or shallow incorporation much gentler on soil life.

Susi Batstone ‏@SusiB348 11. Apr.
Surely the function of the end product is more important than the classification? If it supports plant growth...

Susi Batstone ‏@SusiB348 11. Apr.
The Eden Project soil creation achievement was inspiring, thank you for finding this extract.

Joe Turner ‏@bucksci 11. Apr.
agreed but question was about producing soil.

Joe Turner ‏@bucksci 11. Apr.
even mulches take a long time to be totally incorpoated.

Joe Turner ‏@bucksci 11. Apr.
best option in my opinion is always to add organic matter to existing soil wherever possible.

Elisabeth von Muench ‏@EvMuench 13. Apr.
Perhaps for this material to turn into soil is not the "be all & end all". After all, soil can also be rather infertile!?

Joe Turner ‏@bucksci 13. Apr.
right, it can be a useful growing medium without being a soil. it just wouldn't be so flexible and useful.

Susi Batstone ‏@SusiB348 13. Apr.
Soil as defined by Hans Jenny, requires that it has living organisms in it, that there's organic matter and the mineral component... sand / silt / clay. It can't be soil without life. "

Joe Turner ‏@bucksci 13. Apr.
right, but can it be soil without the mineral content? I'd say no - needs both.

Susi Batstone ‏@SusiB348 13. Apr.
The commercial composts eg John Innes etc,, for long term use, have sand/ grit/ clay added to organic matter. But no orgs

Joe Turner ‏@bucksci 13. Apr.
??? no orgs?

Susi Batstone ‏@SusiB348 13. Apr.
Ran out of space.. No live organisms. It's usually sold as sterile.

Joe Turner ‏@bucksci 13. Apr.
ah. well, no large orgs, likely to be microbes.

Joe Turner ‏@bucksci 13. Apr.
I still wouldn't call this soil.

Joe Turner ‏@bucksci 13. Apr.
many systems work very well without soil, of course.

Susi Batstone ‏@SusiB348 13. Apr.
back to the start - if it Functions as Soil, the correct nomenclature is not the most important thing, surely!

Joe Turner ‏@bucksci 13. Apr. Übersetzung anzeigen
disagree it functions as soil. useful plant medium does not make it a soil.

Joe Turner ‏@bucksci 13. Apr.
for example, the chemical structure and CEC of organic matter is different.

Joe Turner ‏@bucksci 13. Apr.
drainage will be different, erodability. etc.

Joe Turner ‏@bucksci 13. Apr.
it is like comparing chocolate and chocolate cake. one is an ingredient of the other.

Joe Turner ‏@bucksci 13. Apr.
compost has some functions of its own, but many more functions when incorporated fully into soil.

Elisabeth von Muench ‏@EvMuench 15. Apr.
These tweets about soil vs. compost are really interesting. I think I will copy them into a new discussion forum thread.

Thanks to Joe and Susi for teaching me about soil with this twitter conversation!

To all: What is your understanding of soil and compost? Our friends at SOIL in Haiti may have something to say on this matter because they do composting and their acronym is SOIL which is probably no coincidence? ( en.wikipedia.org/wiki/Sustainable_Organi...tegrated_Livelihoods )

Greetings,
Elisabeth


P.S. By the way, did you know that this year is the International Year of Soils? Perhaps we should support our colleagues somehow.
www.fao.org/soils-2015/about/en/

The 68th UN General Assembly declared 2015 the International Year of Soils (IYS) (A/RES/68/232).

The Food and Agriculture Organization of the United Nations has been nominated to implement the IYS 2015, within the framework of the Global Soil Partnership and in collaboration with Governments and the secretariat of the United Nations Convention to Combat Desertification.

The IYS 2015 aims to increase awareness and understanding of the importance of soil for food security and essential ecosystem functions.

The specific objectives of the IYS 2015 are to:

  • Raise full awareness among civil society and decision makers about the profound importance of soil for human life;
  • Educate the public about the crucial role soil plays in food security, climate change adaptation and mitigation, essential ecosystem services, poverty alleviation and sustainable development;
  • Support effective policies and actions for the sustainable management and protection of soil resources;
  • Promote investment in sustainable soil management activities to develop and maintain healthy soils for different land users and population groups;
  • Strengthen initiatives in connection with the SDG process (Sustainable Development Goals) and Post-2015 agenda;
  • Advocate for rapid capacity enhancement for soil information collection and monitoring at all levels (global, regional and national).

Head moderator of this Discussion Forum
(under consultancy contract with Skat Foundation funded by WSSCC)

Dr. Elisabeth von Muench
Independent consultant located in Brisbane, Australia
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Twitter: @EvMuench
Founder of WikiProject Sanitation: en.wikipedia.org/wiki/Wikipedia:WikiProject_Sanitation
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  • joeturner
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Also perhaps harder to get across is that material which looks like soil does not necessarily have all the properties of soil. And materials which may have fully composted and/or been sanitised may not have much agronomic benefit.

As David Bates recently described, material from the UDDTs he studied (which most, but not all, wouldn't describe as compost) was high in pH and had very few options where it could be used to promote crop growth.
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  • antonini
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Here's a link to the Soil Atlas 2015 which contains really nice infographics!

See p.12 (The Invisible Ecosystem) for a general description of soils and their fertility!

If you are interested in this topic, have a look at Global Soil Week which is currently being held in Berlin!

Best,
Samantha
Dr. Samantha Antonini
University of Bonn
Center for Development Research (ZEFb)
Walter-Flex-Str. 3
53113 Bonn
Germany
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Somewhat related is the concept of "peak soil":
www.theguardian.com/environment/earth-in...sation-eating-itself
And while adding compost like substances to soil can help soil preservation, land degradation is a serious issue which can not be reversed easily.

I also think that one should also highlight that it is symbiotic fungi, so called mycorrhiza ( en.wikipedia.org/wiki/Mycorrhiza ) that form an important part of soil life and which will probably not be found in compost.

@Joe: I am not a soil expert, but isn't soil acidification especially in the tropics a quite serious issue? I guess adding high pH UDDT material to such soils would help no?
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Yes, liming can help with acidic soils. But the point is that high pH material can only usefully be used in specific circumstances. One would need to know the pH of the material and the soil it was to be added to and then apply in the right amount. Liming the wrong soils can make them less fertile and can cause problems to a crop.
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

This soil profile is how civil (geotechnical) engineers view soil, with the 3 main components on each side of the triangle: sand, silt and clay. Loam is a constituent also



C:\fakepath\Soil Profile in color.htm

These soil profiles are usually used to classify soils for their structural properties, not agricultural value, but it gives you another perspectives on what civil engineers view what "soil" consist of
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

I'm sorry to disagree, DrBates, but the soil texture triangle you have provided here is widely used by soil scientists. And it has an enormous impact on the agronomic value of land, because the predominent soil texture will determine many things about the workability and fertility of the soil.

Note also that this is not a soil profile, which is a different thing.

en.wikipedia.org/wiki/Soil_texture

I can define soil profile if anyone is interested.

But to reinforce, these are not only geotechnical terms, but are very much terms used by soil scientists to assess agricultural land. Geotechnics is the study of engineering properties of soil.
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

All of that said, it does illustrate that soil scientists consider the mineral make-up of soil to be very important.

Very organic soils (like peats) do not have a soil texture nor do composts.
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Joe:

Thanks for clarifying....I was limiting my statement to the extent of my knowledge of the triangle's use....this is what we used in Geotechnical Civil Engineering class for civil purposes..building roads, etc.

Glad to see the soil scientists use it also

My point in presenting the triangle was to show the three-fold aspect of soil, per this triangle, plus loam. I always found the graphic way of presenting this definition of soil, was useful in understanding what "soil is"
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Yes Joe...that was my point....soil classification focuses on the minerals
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

In the analysis Joe refers to, here was one of the conclusions of that 1 sample:


"The results indicate that the alkalinity was the limiting factor, which
controlled the application rate. The waste would have to be applied at 1/10” to prevent harm to existing soils. This application rate could continue for 20 years without harm to the soils."

At the very thin application of 1/10", it was obvious that the plants were not going to receive much nutrients. And in this case, it wouldn't harm the soil, because I limited restricted the application rate to 1/10". Another words, as an agricultural amendment, it was not beneficial
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Re: What is the difference between soil and compost? Results from a twitter conversation with Joe and Susi

Unfortunately there is a bit of a problem - because the term 'soil' means several different things. In the context David is using above, "soil" means soil texture. This is not really a correct way to try to define soils, but really a facet of a soil, comparable to describing the sharpness of a knife.

So we might say that the soils in a field were predominantly clay. This is shorthand, because soils vary considerably spatially.

But, (again!) unfortunately, soil classification is also the wrong term and refers to something else. And soils can be organic, if they are composed of a large amount of organic material. The point is that you don't use this triangle, because it is only relevant for mineral soils - other soils exist.

Again, I appreciate this sounds very technical and boring, but this is the way it is. Soil Science is more complicated than many think!

On the fertility point, I would say that David's sample would be hard to apply in amounts which would not give a negative effect on the fields he has to spread them on. Too much would likely have a negative effect.

But the main problem (other than the pH) is that those particular soils are already pretty high in nitrogen, so adding more is not going to be doing anything anyway. Crop growth is not going to be limited by nitrogen.

If there was really a problem with acid soils, then one would be better off using the lime directly on the soil rather than in the latrine (of course, this is not ideal given the need for sanitation, so there is a conflict).
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