Composting - the role of Microorganisms

Hi. It is known that so-called "microorganisms" help with composting by "breaking down" organic matter. Can anyone help me to understand what is meant, practically and physically, by breaking down? What kinds of creatures do these microorganisms consist of? How many are invisible? Do they eat the material and produce waste? Does their body heat help the material to compost quicker? What, practically, happens?

 

The way I understand it (which largely comes from books rather than practical experience, as I don't have a microscope), is as follows.

The micro-organisms are largely bacteria and fungi. In a way the 'eat' the material, each adapted to specific roles, with different abilities to suit different materials. Fungi is capable of breaking down lignin, which is the stuff that makes wood woody. Various bacteria consume different minerals, thus breaking down the materials.

There are also other consumers. Woodlice for example will help chew up dead plant matter, as do slugs and snails and worms.

All of these organisms, like all living things, have several things in common:

* They all need food and water - the compost material
* They all need warmth to varying degrees
* They all excrete their own waste
* They all breed
* They all generate body heat

Its the last two points that makes a good compost heap warm up, because if conditions are just right, the organisms will breed and therefore multiply, and more of them means more body heat. More heat means the microbes can be more active, and so a chain reaction sort of happens.

According to the very informative book I have, in some conditions a compost heap can reach 92 degrees centigrade at its hottest point, but I think that's unlikely in a smaller heap.

According to the same book, something very interesting happens when the temperature gets to about 60 degrees centigrade. It gets too hot for most of the microbes, and they die off, BUT, another set of microbes that are dormant or sluggish up to this point suddenly find the conditions ideal, and they breed like mad. This second set apparently break down dead plant matter much more quickly, and breed like crazy, and can happily thrive at close to 100 degrees C, with their ideal temperature being around 80 degrees C.

In large scale composting, these temperatures can be achieved, and compost can go from fresh material to rich, sterile compost in just a few weeks, but the typical garden heap will not be large enough to reach 'critical mass' for the higher temperature microbes, and so will take considerably longer to rot.

 

Thanks, though I am still in the dark as to what exactly happens. Even in your very informative answer you say that microbes "eat" organic matter, the inverted commas suggesting that what actually happens in a mystery. I would like to know how they break down the organic matter, and how, if is is eaten by mcrobes, this organic matter still appears in the compost bin.

 

Hi Simon,

I'm no expert either but I can offer some observation.

A pot filled 1 inch from the rim wih compost and planted up in March, will by September be nearly 2 inches from the rim, partly due to settlement but also (as I think) that composting carries on and the further breaking down of the compost is what actually feeds your plants. I have often thought that if left for long enough a compost heap could probably disappear altogether..that's an extreme view of course but I have partly seen this happen with pots or baskets of compost here and there.

What I think is key here is that the initial composting which gives a nice crumbly black rich smelling compost is just the first stage in the composts total breakdown with reference to my extreme view above, and is the point at which it becomes very useful to the gardener. The microbes/bugs have been eating at it for a while but have not eaten all of it, hence why you still have "organic matter" in your compost bin.

I hope this helps, but remember its just my thoughts/observations.

Steve...

 

I'm having to dredge up distant memories of biology classes at school now, so I might get this wrong, but here goes:

Bacteria and fungi don't have teeth and jaws and a digestive system as such, so they can't really eat the compost material. Instead they secret chemicals that very slowly dissolve the material, and they absorb the minerals that are released from that reaction, which gives them the energy they need to live and breed.

The reason why you still have compost left after this process is twofold. Firstly, the composting process will slow down to almost a standstill once the bits that are easy to break down have broken down. The microbes take much longer to break down tougher chemical bonds. Secondly, all these things excrete waste.'

If you had long enough to watch, eventually your compost would be reduced to the minerals it is composed of, but that's going to take a very long time.

 

Super article here >

Role of Microbes in Ecosystems

and there's lots more on the www if you search for microbial decomposition.

 

Wow, that's a great article: thanks! I particularly like the line, "Microbes can do anything they want, wherever they want." Pretty much sums it up, I think.

 

If I were to place a video recorder underground would it be possible to see a worm "eat" organic matter; or is this a microscopic process that, as with the microbes described above, takes a very long time?

 

In nature the microbes eat back decaying matter on roots, taking the root back to good. The clean root grows into the nutritional excretions of the microbes.

An organic compost is a macro herd good to go..

Liquid seaweed feeds keeps the herd tip-top.

 

It's all chemistry, all food from your bestest steak dinner to rotting veg is broken down to the chemical compounds required by the organism that is digesting it.
Different bugs will have different enzymes and systems to break down specific foods for their requirements a bit like how our digestive system can cope with different foods than grazing animals.
Like we have our preferred dining conditions (on a tray in front of fire and telly) bugs also have optimal conditions for dining, if the temperature, pH oxygen levels aren't right for them, they won't "eat" and your compost doesn't get converted. Different bugs have different requirements for these conditions, same for worms and maggots.

Looking at my compost heap I think the microbe environmental health inspectors shut it down.

D

 

Can't say I've ever tried that one

 

So a small piece of onion peel in a compost heap will be broken up ("decomposed") via microbial secretion, and if I had a microscope powerful enough I would be able to actually see where tiny bits of it had disappeared?

 

read this article .... it covers some of the questions asked

http://www.microbeorganics.com/#What_is_Compost_Tea_